The Weird World Of FM Subcarrier Broadcasting
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- เผยแพร่เมื่อ 23 ก.ย. 2017
- Video killed the Radio Star.... but once upon a time, there was the fascinating realm of private subscription FM subcarrier radio!! Join Team FranLab!!!! Become a patron and help support my TH-cam Channel on Patreon: / frantone
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I am a music programmer (aka "DJ") for our NPR station here in Humboldt County, California - KHSU 90.5. We still use our sub-carrier signal to broadcast to blind and sight-impaired individuals. A local non-profit (Volunteer Services of the Redwoods) has people who read the local newspaper and other periodicals - over the air - on a daily basis. No subscriptions - the radios are handed out to those who need them. I suspect there are similar operations scattered throughout the country.
We have the same idea here but it's broadcast over the regular airwaves and received by normal radios, so it's free-to-air for anyone who needs it and there's no need for a specially-modified radio to hear this kind of broadcast.
It's really cool for your station to do that and it's awesome that volunteers are stepping up to help people out like that. Thank you!
Same for KPBS in San Diego, where it is called the Radio Reading Service, primarily used to read articles and ads from local newspapers and magazines. I was a volunteer reader about 20 years ago, and have occasionally filled-in since.
Matt Knight WOSU fm in Columbus Ohio has the same thing. It's called "CORRS" Central Ohio radio reading service.
In Newcastle(Australia) in 1999 we had a station doing a trial broadcast for 3 months on 99.7 Mhz FM under the station identification, VIP(Visually Impaired Persons') Radio. I volunteered as panel operator there, in between my sessions at Port Stephens FM(I lived at Stockton at the time, Newcastle was just a ferry ride away while Nelson Bay where PSFM was then, involved a 90-or-so-minutes bus ride). We did our own newspaper readings by taking pieces from The Newcastle Herald. When we weren't live to air ourselves we took a satellite feed off the Radio For The Print Handicapped broadcasts(2RPH, Sydney). Where we were located, in the Civic Arcade, Newcastle(first floor), we had a microwave link pointing up to Mount Sugarloaf, out beyond West Wallsend. During our three-month trial we were beset with problems involving a new luxury apartment building under construction just down the street from us, and when a crane swung into a certain position..... Microwave transmissions are likened to a pencil-thin beam, and if anything gets in their way.... You guessed it, We'd get knocked off the air each time that blasted crane swung into a certain position, but there was nowhere else for our microwave aerial but out the front window. There was another story of woe but I'll save it for later.
I remember making a few SCA converters for myself (which was illegal, but if you weren't selling them, nobody really cared) and the shop I worked for had a contract to set up and repair these radios for two local subscription companies. The radios would typically come from the factory without being tuned for any specified frequency. We would set up the (very tight) notch pass filters to allow only one station be be received while in SCA mode. (Otherwise, you could receive other services, that you weren't paying for, as well.) If I remember correctly, most of the billing was done on the honor system (the company would call subscriber and get the chronometer reading) and was only physically checked once or twice per year. One of the services eventually abandoned the chronometer system and just went 'flat rate' to be more competitive against the other service. The whole system started falling apart in the 80's when offices, beauty salons, doctor's offices, barber shops, etc. realized that their customers really didn't mind hearing a few commercials. As a last ditch effort to save this business model, there was a push in the mid 80's and early 90's to fine businesses who played standard radio for their customers. It was considered "using the radio content to provide entertainment". (It's like the warning on VHS tapes which said that you could only use them in your home and not for audiences.) The law behind it was very loosely based on royalty laws in which bands and mobile DJ's were supposed to keep track of and pay for the songs they used to entertain audiences. (Which very few, if any, did.) The fines levied against businesses were based in a very grey area, to say the least. Let's say that you were a barber and had a radio at your barber station. That was OK. If you placed the radio out in the open and turned it up for your customers to hear, you would get fined. If you connected a remote speaker to the radio to cover a larger area of the barber shop, you would get fined. If you provided music to your customers, even just to make them more comfortable waiting for their car to be repaired or waiting to see a doctor, you would be fined. It was a complete disaster. When the subscription companies finally conceded that they just couldn't force people to pay for radio (and were getting pressure from judges for clogging up court rooms over people fighting the fines), they finally gave up. SCA still exists in some areas, but is mostly used for specialized services and most of the services are free. Some companies like professional offices and hospitals still use music subscription services. Very few are SCA. Now, most are satellite programming. That's about all I remember. I'm sure somebody else can help fill in the blanks or correct anything if I recalled something wrong. Hope that helps. Feel free to ask any other questions. It might jog my memory a bit.
A lot of which you speak about businesses using radio as entertainment has been embraced by the performing rights organizations - so, let's say you're a barber shop with four chairs, and you hook up speakers so that all of your customers can hear what's playing. One day, you'll get a visit from a representative from BMI and ASCAP, who walk in, scope out your setup, and assess you with an annual license fee. The more speakers you have running, the higher the licensing fee will be.
It's not just restricted to radios - a coffee house with no radios was hit with an $1,800 licensing fee from one of the PROs (don't know which one it was) because they had entertainment at night by artists performing their own compositions; the performers had to agree in advance not to perform ANY cover tunes. It didn't matter to the rep - his logic was, there was always a possibility that someone might sneak in a cover of something that the owner wouldn't recognize as such - and then ... well, you can imagine how this could cause the collapse of civilization as we know it.
Between this kind of harebrained thinking and what the DMCA has done to ruin videos virtually everywhere, it's amazing that we know that anything new to listen to is even out there - which, in my opinion, does nothing to help the struggling artists this kind of regulation professes to help.
"A lot of which you speak about businesses using radio as entertainment has been embraced by the performing rights organizations"
Yep, we have it over in the UK with the PPL.
"The law behind it was very loosely based on royalty laws in which bands and mobile DJ's were supposed to keep track of and pay for the songs they used to entertain audiences."
So that's why bands keep a set list. Over here we have the PRS/MCPS requiring broadcasters to keep a log of which tunes they play or even use in TV broadcasts. Unlike the US where radio stations went from Pay-ola (where record labels would pay the stations to play their tunes) to broadcast radio stations not having to pay licence fees (but internet broadcast stations do have to pay, because new techonlogy) the PRS and MCPS have always require all stations to have a licence to play music.
What it means in the UK is for a radio station to operate legally, apart from the licence from OFCOM to broadcast on the public airwaves in the first place, they also need a PRS licence to play music over the radio and a PPL licence to listen to their own broadcast in their own studios.
I actually remember many years ago when American online stations decided on a day of silence in protest of their licence rates going up (the rates that broadcast stations don't have to pay) and American listeners getting upset because the BBC and Last.fm weren't taking part (IIRC this was because CBS bought out Last.fm) what they kept forgetting was the rate increase only affected American based station, and neither the BBC nor Last.fm were US based at the time (an d both were already paying higher licence fees than what the American fees were getting raised to)
When I was on tour through Europe many, many years ago, I had to fill out a form with everything that we were planning to play before every show. This was supposed to make it possible to pay the artists who wrote the songs that made the whole world sing - a lot of my songs were on that list. To date, I haven't seen a cent.
Roland, the fine print might say that you have to claim the royalties, and that there is a time expiry on claims, along with an administration fee! Those organisations most likely could not exist without such shenanigans. They're like insurance companies in those respects.
They (the radio/music industry) still try to enforce licensing. You’re still supposed to pay I think it’s RIAA if you play music from the radio, or pay for business access if you’re using consumer satellite (directv or dish) radio service. They consider it a performance of the music. They definitely get their pound of flesh from a lot of places even if it’s marginal at best legally.
I was a volunteer at a local FM station in 1968. The station had huge audio tapes that supplied the sub-carrier with Musak. Never figured out how they sold it.
In the early '70's, my wife worked in an realty office that had this same style of radio with the chronometer on the back. Every 3 months someone would come into the office and take the reading off the chronometer, then a week or so later, they'd receive a bill in the mail for the amount of time the "service" was used. It was metered like electricity.......
I used to work for a company named American Quotation Systems originally in Rochester MN and later moved to Champaign Il.. I would install McMartin receivers in grain elevators and farmers homes to receive the Chicago Board of Trade quotes for corn and bean prices. We used the SCÀ on numerous radio stations across the midwest. We had our signal originate on KROC in Rochester then install a radio receiver in Waterloo IA at KWWL that picked up KROC. We would then feed the audio onto the SCA of KWWL. The next hop was to either Carol IA going west or to Moline IL eastbound. Eventually we covered from Nebraska to Indiana and Minnesota to Kansas. My job entailed installing antenas on the radio station towers to connect our networks and on the legs of grain bins or on top of a grain silo and run the coax from it to the sca radio in the office. I usually would have it located near the scales so farmers knew what they would get for their corn or soy beans as they were being weigh or unloading. The radios could be tuned to any station by changing the crystal to each station using a formula of the frequency minus 10.7 devided by 2. So 96.7 was minus 10.7 equaled 86 divided by 2 so I would install a 43 mhź crystal. The tr66 was the most popular unit installed. There was a switch so you could listen to main radio station or the SCA. Unfortunatly many folks didnt care for the station we used ie Ròck or country Music so the left them om the SCA. I had installed 100s of the units at almost every grain company in every town in Iowa and illinois. Eventually I left to work for a large computer company and Reuters bought the lock stock and barrel of AQS. Computer type terminals were coming out and replaced the radio, with the data then sent via the same SCA signal and demodulated to print. on a screen. Progress in the mid 70's
Thanks for this random bit of history I had zero clue about, from a world before me
@@FlyNAA Glad you enjoyed the history of one of the numerous uses of the SCA signal on the FM band. Muzak and reading for the blind were also using the SCA.
When I was a kid, nobody believed me when I told them that AM broadcasts bounce off the ionosphere, and was the reason some stations weren't available a few hours after sunset.
It used to drive me nuts when Radio 1 in the UK was only on AM, john peel's show would only be half way through before it faded out.
Thats not totally how it works. Stations would also lower their power at night to protect other stations as the D layer faded after sunset. ( I think i got that somewhat correct ;0)
It is more frequency dependant than mode. The frequency range of traditional "AM Radio" (roughly .5MHz to 2MHz) is limited in distance during the daylight hours by ionospheric D layer absorption. After local sunset, the D layer (which is the lowest layer) dissipates and radio stations in that frequency range can be heard via "skywave" aka ionospheric propagation in addition to "groundwave."
@@thomasdavis4253 Yes, it's quite common to have debates which get very mixed up regarding the comparison between AM and FM and the comparison between the frequency bands they use.
All the really hip people never listened to Radio one in the evening in U.K. ,they tuned into Radio Luxembourg instead .You must of been a square .
I was an engineer at WPKM, which was a small FM station in Tampa. They ran "Southern Melody" on their subcarrier. There was a pair of Reel to reel machines that alternated back and forth with huge reels on it.. Typically 24 hours of playback from 2 rolls of tape. They charged for the background music some amount that depended on the client. (One was a dying shopping center that had about 50-100 speakers on the outside where the Southern Melody played.. We had to yank all that equipment when the bull dozers were ordered for the shopping center. They had been paying a lot of money to keep the folk walking around entertained. The station got sold, Souther Melody vanished from Tampa.. and it started with a new (and MUCH more powerful transmitter, now on a bank downtown) format... The Q morning zoo started there.. then one of the folk moved to NY to start it up there....
"Fran" is obviously her mild-mannered alter-ego. There's no way this woman isn't out fighting crime at night. Undoing dastardly deeds by nefarious characters and saving the world at the last second.
yogibear2k10 She's the one who told them what stunts to do. "I remember this one time when..."
I imagine her as a groupie that toured with bands like Steve Miller and Boston...
I think she has a really sexy voice!
SaturnV2000: Eh? You're joking surely?
It's what guys say so they don't feel as bad about getting shot down. LOL!
Just a current datapoint: using an RTL-SDR and Redhawk, managed to spin an SCA receiver to play the "Sight into Sound" service for the blind on KUT in Austin (90.5MHz, subcarrier at 92KHz). As an aside, also got a crude RBDS decoder working with the same setup. It was lots of fun. Felt like a kid making a secret decrypter ring!
I found this article about it.
DOCTOR'S RADIO NETWORK TO GO OFF THE AIR MAY 31
Published: May 21, 1981
The Physicians Radio Network, a round-the-clock service sponsored by several giant pharmaceutical companies, will discontinue broadcasts on May 31.
In 1974, Visual Information Systems, a division of the Republic Corporation, initiated the station exclusively for doctors - it currently reaches 80,000 physicians in 69 cities. Jay E. Raeben, president of Visual Information, said that his company had ''failed to persuade enough of the industry that the radio was a medium important to use.''
Transmitting on an FM sideband frequency, or subchannel, which could not be picked up on a standard radio dial, the network permitted doctors to communicate among themselves, more freely perhaps than might be possible before a listening lay public. This feature, however, contributed to the station's downfall. The necessary special receivers were distributed to doctors upon request and without charge. Mr. Raeben said that the cost of manufacturing and mailing such equipment had diminished revenues substantially. Used by Advertisers
Physicians rank as the profession most vigorously sought by adverstisers, because their prescriptions largely determine the profits of billion-dollar drug companies.
''Surveys show that P.R.N. affected sales very positively, especially as it impacted new products,'' said Robert E. Devinna, director of advertising for Roche Laboratories, one of the sponsoring companies. Eight minutes of every hour on the air are devoted to advertising. Programming focused on scientific breakthroughs and significant operations, such as the recent surgery on the Pope.
''P.R.N. rarely announces new drugs,'' said Mr. Raeben, who also acts as managing director of the station. ''We made a very considerable effort to insure that programming was not in the interest of the advertisers.'' If a new drug were announced, it would have to be newsworthy in itself, he asserted. May Turn to Journals
Mr. Devinna of Roche Laboratories thinks that some of the major drug companies that advertised on the network will probably turn more to medical journals now. He views this as ''shortsightedness of the marketing industry,'' and added, ''Traditional advertising channels are cluttered - it's a shame to see P.R.N. die.''
The end of Physicians Radio Network will apparently not work any great hardship on its originator. ''Republic Corporation does not expect to lose any money due to the termination of P.R.N.,'' Rembrandt P. Lane, an executive vice president, said
He said that Republic had tried unsuccessfully to sell the station, which had, in fact, been profitable for the last three years. ''P.R.N. is a very small investment by a division of Republic Corporation,'' Mr. Lane said, ''having a limited marketplace - and the 80,000 subscribing doctors paid nothing for the service or the radio.''
Mr. Lane declined to specify the operating expenses of the network, or Republic's initial investment.
PRN was on one station in Chicago. I built a decoder for SCA, which was easy to use since I had a Pioneer quad receiver that had jacks for an external quadraphonic subcarrier decoder. I am trying to recall if the music services died before PRN did.
The pharmaceuticals later figured out that if they could lift the band on advertising directly to the public that that would be a better way to boost profits versus trying to get doctors to prescribe a new drug. Instead have the public demand the new drug from their doctor, ala "Ask your doctor." we now see in direct to consumer (DTC) pharmaceuticals ads on the evening news. (something only allowed in U.S. and New Zealand) That has reaped them many tens of thousand return on investment than any little radio network could that PRN was.
Marcus Damberger Awesome comment. Glad to finally see why. Lol WHY shut down an otherwise profitable business.
Fran, back in the 70’s & 80’s I was involved in operating 6 FM stations. We leased our subcarriers out, not to PRN, but to several other companies that provided subscription services. One was an agricultural info channel sold to area farmers. One company provided a one-way “digital” data service that fed data receivers that provided real time commodity pricing and market data. Of course the signal was analog, but a tone signal was broadcast and received as data. The audio sounded much like an old 128 baud modem. Anyway, it wasn’t always the station that sold the subscription service. All we did was lease out the subcarriers. We called it “easy money”!
Excellent! Way back when I was a poor ham operator college student, I built a simple adapter for SCA reception. There were easily 7 or 8 Muzak channels on the Chicago FM dial, plus PRN, NPR reading service for the blind, and stock quote encrypted modem tones for a paid subscription zero- delay stock quote service. The modem tones were Bell 202 modem tones. I used a ham radio packet radio TNC in dumb modem mode to try to decode. No luck.
My SCA adapter used the old Signetics NE565 phase locked loop chip and a passive low pass filter to cut out main channel audio bleed through. These chips were very static-sensitive and the oscillator circuit in the chip would frequently blow. I added a tuning pot to mine to switch between the two popular ultrasonic carrier frequencies. You needed to tap the demodulator audio output before the de-emphasis capacitor, which would shunt the SCA carrier from the received audio.
Recently, I used two daisy-chained SDR dongles to recover the SCA audio. The secondary channel was also FM, but narrow band with low deviation. Amazingly, there’s still a few stations broadcasting in the Chicago area. The doctor my wife worked for back in the 70s had this identical PRN radio in his office at the time. Half of the PRN programming was drug ads. This was back when it was illegal to advertise prescription drugs directly to consumers.
I'M IN LOVE with your channel!
I learned about the 'storecaster' sub-band as a child, from my Dad who designed radios for GE in Utica, NY.
They designed and built many good radios. I have most of Superadios and other pocket radios. Being born and raised in Utica they are very special.
"Empire Of The Air" is an Amazing series to watch. I'm a big fan of Lee DeForest. A few months ago, I was extremely fortunate to come across a box full of brand new Lee DeForest Audion tubes in their original packaging. SCORE!!! LOL Yesterday, while antique shopping, I purchased a 1913 single tube regenerative amateur radio receiver which was complete and in great condition. It required the usual cleaning and such, but the glass envelope of the tube was separated from it's base and the wires weren't long enough to reattach. Lee DeForest to the rescue!!! I used one of the Audions to complete the restoration and it's playing beside me right now.
th-cam.com/video/CKBMGR8fUzc/w-d-xo.html There it is the Ken Burns PBS movie and it will be 26 years ago come Jan, 2018 when it aired. Damn time flies.
Well then, since you watched "empire of the air" you know that Mr. De Forrest had no idea how the audio worked and with some partners, defrauded people out of their money. Just another con artist.
William J. Also electroboom is a really engaging uh "hands on" demonstration of electricity.
Also the best nugget of information i've ever found was this. www.ibiblio.org/kuphaldt/electricCircuits/DC/
Lessons in electrical circuits by Tony R. Kuphaldt.
It's a practical text on electrical theory as well as circuits. It's amazing and a great standalone book without the need for a teacher or lecture.
Thanks, Shemp, for a link to the documentary Fran mentioned. And thanks, TK TK, for the link to that free electronics text. I've been wanting to increase my meager electronics abilities for a long time, and was hoping there was something like that out there.
I've managed to find another version that's free to watch.
Ken Burns's America, Empire of the Air: The Men Who Made Radio
search.alexanderstreet.com/view/work/bibliographic_entity%7Cvideo_work%7C1787322?account_id=12492&usage_group_id=100865
When I was young, I worked at a hotel which played Muzak. I loved the stuff. Then I found out it was received off this McMartin multiplex receiver, and not via leased telephone lines as it used to be sent out. I built a makeshift, add on detector for my tuner, but later learned the crystal controlled single channel models were way better. I played Muzak at the house nearly 20 years. My mom loved the instrumentals. Thanks for showing the world a little known part of FM broadasting which I too discovered at a rather young age.
Looks like PRN was a short-lived venture. Found a NYT article in May 1975 announcing its launch after a year of testing, and another article in May 1981 announcing its termination.
Thanks for the video! Fascinating.
Naming it PRN (Physician's Radio Network) was a mildly clever little play on words.
So, "prn" is a medical abbreviation (or more precisely an initialism). It's latin for pro re nata. By convention, doctors still write prescriptions in Latin abbreviations. "Prn" is a very common one and it's probably one of the abbreviations most well known by people who aren't in the medical field. It means "as needed" which is the most commonly used english translation and is what you'll see on your prescription label if it was written prn. Maybe a more literal translation is "as the circumstance arises."
If you take a pill twice a day, for example, and you're meant to take it continuously without skipping any, your doctor will write the Sig (which means directions) as: i po BID (the i means 1 and it's actually written like an upper case T with a dot on top but small like the lower case letters, there's just no character for it that I can type as far as I know).
BUT, if your doctor only wants you to take it only as needed, like xanax or a pain pill or something where if there's no pain or no anxiety at that time, then don't take it, then your doctor will write: i po BID prn (which means 1 by mouth twice daily as needed).
I know I'm rambling on but I just thought I'd share. It was mildly amusing to me lol.
Also the cipher H.S. stands for Hour Of Sleep which means take the pill at bedtime, and in eye doctor lingo O.D. is Optical Dexterous which is Right Eye and O.S. is Optical Sinister which is Left Eye, which also explains why a left-handed compliment is sinister. Some cultures aren't kind to southpaws.
Hi. When young and still in high school, I learned how to build my own SCA decoder using an NE565 phase locked loop chip, and you can still find them on ebay. A project of how to build it was published in Radio Electronics magazine but it was just a real simple circuit that only kinda worked. It needs a good 67Khz band pass filter in front of the PLL chip or it won't work right. I kept buying grab bags of assorted coils from radio shack to try and build the filter and was finally able to get pretty good results. All my high school friends hated the music though and thought I was pretty weird. There was radio reading for the blind and for a few years was the physicians radio network which was the most interesting.
Getting older, learned more about electronics and got better at building SCA decoder circuits and eventually used an FM IF chip like the MC3357 to up-convert the 67Khz to 455Khz and use a 455Khz ceramic filter and a resonator to demodulate the SCA signal. I still have one in an old GE super radio that can switch to either 67Khz or 92Khz.
I built my own little FM stereo transmitter which also has an SCA exciter built using an 8038 function generator chip tuned to 67Khz with the audio going through about a 5khz low pass filter and then a 150us pre-emphases network to modulate the 67Khz sine wave oscillator that uses the 8038 chip. The transmitter still works and I have a long playlist of good background music on an MP3 player I can connect to it.
The SCA from that transmitter still comes through on that old GE Super Radio. You need one of these to go with that old radio you have.
One of the Australian electronics magazines, I think Electronics Australia, published a subcarrier decoder kit, known as SRS or supplementary radio service. The kit was super simple, the main component was a 4046 PLL chip. Here there were three main subcarrier frequencies, though the most used by any given station was two as I recall. The kit included a pot to allow you to tune it to the different subcarrier frequencies. The subcarrier modulation was FM, hence the need for the PLL.
I know you will get a kick out of this Fran. When I rebuilt my first street bike when I was 16 it was a Kawasaki H1500.
It had one of the first production CDI units. (That I know of). Two large boxes mounted under the seat. When I would come home at night, my parents (in the finished basement, watching TV (pre cable) ) knew I was home because the antenna for the TV was in the attic whose wall intersected the garage. The CDI was so "unshielded" that it made the TV picture get all wavy. (I think I got complaints and checked it out myself by idling my bike in the garage and then going down to look at the TV.) Sure enough, it had an obvious effect on the picture. After my discovery, I always came home and shut my bike off as quickly as I could. At least Mom and Dad knew I survived yet another day of riding. That was '79.
Good timing on this. I'm going through my subscriptions and you're talking about FM Subcarrier which is cool enough on it's own. To add to it, All American Five Radio came out with a video right after this that breaks down the composition of what a modulated FM Stereo carrier looks like. It's super neat. What a treat from both of you!
So I went and found a copy of Empire of the Air: The Men Who Invented Radio, as you suggested. It was most fascinating! Although I had heard of Lee DeForest, Howard Armstrong, and David Sarnoff before, I was completely unaware of the intertwinement of their lives. It’s interesting how much David Sarnoff, 100 years ago, was like Steve Jobs, 40 years ago - taking other people’s inventions and combining/marketing/corporatizing them in a way that no one else had thought of before, and thus eventually creating a company that (at the time) rivaled no other. And he was kind of an ass, too. I guess that personality trait is necessary to achieve the level of success they both achieved.
Anyway, it was most definitely an interesting and informative documentary, and thank you for recommending it.
@molson12oz Like they say...the only unfair fight is the one that you lose.
Still broadcasting FM stereo radio in UK…I can remember when living in Swansea UK centre when Kilvey went stereo and I put up a 6 element aerial and my red light lit up on my Korting receiver.
Now I have all my LPs some worth a small fortune…integrated into my satellite/ broadband/Blu-ray ATMOS system.
My dad was a big ham radio collector and antique and radio enthusiast and I went to school for broadcasting, where I spent a lot of time learning about HD radio, and yet I STILL never heard of this! I can't believe it. FM stations now have the ability to split their signals into three digital signals, so they can have three different broadcast. But you need a special digital radio to pick them up. When I went to college for radio from 2004-2008, everyone was making such a big deal about HD and thinking that was going to be the future. But I never hear anything about it anymore. I volunteered at a classical station that had an HD jazz station. I worked on the jazz stuff. But that was the only station I know of that really did anything noteworthy with the HD format.
And YES, they have an open-source HD Radio Decoder that can run on Linux Mint using the RTL-SDR dongle. I recorded about 6 hours of Big 101.3 on HD Radio Carrier 2 from 98.1 MHz Cat Country plus the Cat Country HD Carrier 1 and the analog FM signal in one file. And if you solder to a point on the circuit board of the RTL-SDR you can also tune to 1.2 MHz in direct sampling mode at 2.4 Million Samples Per Second and create a record of the ENTIRE AM radio band...as in you can listen to a station on one frequency, then *rewind the radio* to another frequency that was broadcasting at the time you heard the first frequency...A 25 billion character Blu-Ray recordable disc can hold about 1 hour and 25 minutes uncompressed.
FM subcarriers are still in use, at least in big cities with large ethnic populations, as most of the subcarriers in use today are providing foreign language programming. Most subcarrier receivers are fixed to one frequency; I've never seen a design like this before which provides a tuning dial but uses microswitches to limit the subcarrier tuning range. I guess when doctors were paying for the subcarrier service by the minute, they could afford to make such a complex design!
Shango066 repaired one of these with tunable subcarriers... very interesting world music broadcasts
VWestlife wow it’s nice to see VWestlife checking in here!
Australia's SBS radio stations broadcast mainly on AM, on frequencies which were, in some cases, vacated by stations that had switched to FM. SBS is the Special Broadcasting Service, running programmes on regular broadcast band frequencies without the use of, or the need for subcarriers. Programmes presented in Macedonian, Greek, Lithuanian, German, French, Italian and other languages are simply scheduled for regular timeslots in a week's broadcasting. Using subcarriers adds a layer of complexity that is totally unnecessary.
postersm 71 I’ll second that! What a legend 👍🏻
ahh yes the beauties of clandestine public communication.
Hi Fran - I'm now retired, but had a very enjoyable and rewarding career as an electronics engineer. I still have a lab at home and work on electronics of every vintage. Everything from tubes to surface mount. Anyway..... a few years ago, my wife started showing some interest in electronics. To say I was happy about it would be a huge understatement! :-) The first project I had her build was the Ice Tube Clock from Adafruit. I'm not sure if you're familiar with that kit, but it's extremely challenging for a beginner. I coached her through it, but made sure that she did ALL of the soldering herself and that she also understood what all the components did. I was very proud of her for completing it. When she finished it, I told her "If you can do that, the rest is easy!" We are now expanding my home lab to make room for her to have her own bench, test equipment and work area. Do you have any encouraging videos for women who want to get interested in electronics or could you make one? I want to keep her interest in electronics going and a few words from you could sure help with that. Either way, I thank you for all of these enjoyable videos. You and I have a lot of similar niche interests in electronics (such as our collections of vintage L.E.D.'s!!!) and it's awesome when I find videos of yours that explore one of these specific topics. Take care and thank you!
Hi William, Check out TH-camr Mr Carlsons Lab. He is a very knowledgeable guy and he breaks it down well enough for beginners to understand. If I can learn something from his videos, Your wife certainly can.
William J.
Also check out the soldering vid by CuriousInventor.
It covers many of the common beginner mistakes, so should help a lot with the basics. ;)
EEVblog is another go-to channel for general electronics.
He more often just shows cool gadgets or test equipment, but has also made a lot of in-depth vids on electronic theory too.
You should try your hand at making a few videos for your channel.
William J. That's so cool, I need a husband like you! Where should I look?
William J. - this is a fantastic story...this is You-Tube at its best. BTW, it's a pleasant surprise that my Cricket Wireless 12GB data limit actually turns out to be enough to allow quite a bit of You-Tube and TuneIn streaming. This is my first cellular plan...
Back in the 1940s, when Q102 was WFIL-FM, "fax over FM" was experimented with. Philadelphia Inquirer used the subcarrier to transmit faxes to specialized FM fax machines under the WFIL-FX callsign. People that used the service would get the latest news before it hit the newspaper. The equipment was too expensive and the service ended after a couple years. Fun Philly fact :)
I actually have an old GE super radio, that has a little kit in it. And there’s all kinds of interesting stuff still on the sub carriers. And that thing is sensitive enough that you can hear some pretty interesting stuff
Thanks Fran! I do appreciate AM a lot including the statics in winter time :), kinda nostalgia of a book based simple life, when I was a kid sitting next to my dad tuning SW stations and hearing lots of foreign musics and unknown languages and trying to guess what it was :)
yet I was excited when later on, we purchased a boombox with a fm stereo indicator and we were full of excitement when that LED lights up, this didn't kill the passion of SWLing: that was our internet back then
Had my crystal radio from Kix cereal picking up stations in NY & wherever
Steely Dan! Back in the 80’s as an elementary school student, I made my own crystal set with the germanium diode. I loved the wonder of that set.
SCA originally stood for Subsidiary Communications Authority, much in the same way that JPG stands for Joint Photographic Group. Over the years it began to be known as Sub-Carrier Audio.
PRN also used to do a talk network aimed at information for doctors. My friend used to install SCA converters in radios. We also had a station that carried the ABC Radio Networks on their subcarrier and of course there were background music services like Muzak. Fun times to discover this hidden audio.
Wow! I never learned this stuff from my dad! I have now learned a whole lot about FM radio!
Fran I enjoyed that being a retired dentist I had one of those in the early eighties. However, the reason I posted was about the shot of the album cover from Steely Dan. If you look closely at that photo you will see a disembodied hand on the console. That is unless the guy with his boots on the console has 2 left hands. Let's just say that a group of us discovered this in an altered state way back in the day and it has puzzled us to this very day.. I even mumbled "No static at all" when you said "FM".......forgive my musings
I had no idea FM was a steely Dan song until you said. I know this version - th-cam.com/video/ueKxBPb7yO4/w-d-xo.html
@@medes5597 That's terrible. Simply awful.
@@blueridgerennsport the Mountain Goats are wonderful and beautiful and no he cannot sing and yes he is a poor guitar player but... I had a point here I swear.
Part of what took so long for FM to gain popularity was the FCC first allocated one frequency band then then 88-108 band. The inventor of FM was Edwin Armstrong - he got shafted - part of it compliments of RCA and Sarnoff.
your Steely Dan drop at 4:49 is the coolest thing. You rock Fran.
Messing with those slugs was a poor idea...even if you DO manage to find a station, you still may not get reception...those coil adjustments can be critical.
Also, SCA needs a strong signal, so the antenna needs to be extended(unless the station is REALLY strong).
Disabling that switch is necessary...then find a list of SCA enabled stations in your area...then tune one of them in on the normal
FM mode, then switch the SCA on...then you might have some luck tuning the coils.
Most non-data SCA signals use a 67 Khz Subcarrier, but there are others also.
With a commercial FM station, SCA can be used to monitor the transmitter. ie data is sent back to the studio about the transmitters condition via SCA. This is mentioned as " Frequency and modulation monitor system for stereo and SCA. SCA required for telemetry monitoring." costing 10k as line item 8 from the bottom on this spreadsheet: www.ntia.doc.gov/legacy/otiahome/ptfp/application/equipcost_Radio.html
Monitoring for the Stereo Pilot and subsequent sub-carriers is a given, or must. As you have to monitor your FM deviation and stay within your channel. All FM stereo monitors like those made by TFT (now gone... like this TFT Time & Frequency Technology 724A Stereo Modulation Monitor www.torontosurplus.com/a-v-photo-computer/audio-visual-equipment-accessories/tft-time-and-frequency-technology-724a-stereo-modulation-monitor.html) have the ability to monitor your stereo pilot along with the sub carriers at 38kHz (Left-Right sub-carrier) and 67KHz (where reading service etc or SCA would be) . To use the SCA subcarrier as your telemetry return channel would prove problematic if your transmitter went off the air or had signal problems. You wouldn't be able to diagnose anything. If your 50 miles from your transmitter and an hour away drive time, that can get rather tiring. Also if you have a low power backup transmitter that's hard to pickup the SCA subcarrier from, you would still have telemetry return issues. In theory you could piggyback your telemetry on your STL (Studio Transmitter Link) on the SCA and filter that out at the transmitter site, and some stations might have done that. But most STL microwave transmitters had a subcarrier module for this purpose outside of the FM composite signal that was generated at the studio. (now your SCA is occupied with data instead of reading service etc..) But that does not get a return telemetry, So most would put up a 900MHz microwave link back to the studio for telemetry. Other stations used a phone line they ether called or had a dedicated circuit open for telemetry only, something like a voice grade data modem with 1200-9600pbs is all it takes to monitor a transmitter full time. Most would probably just be set to 56kbps now. I suspect more modern versions would just use cellular data service if available, but your at the mercy of cellular networks being down if there are widespread outages.
@Fran
I was waiting and waiting for you to say the magic word - I don't think I heard you say it. It's multiplex! 🤗🤗
The mystery chip is most likely the Signetics NE565 PLL decoder IC. I bought a kit with one of those boards and assembled it long ago. Today (Oct 2020) most FM stations in the US have gone to HD Radio with the digital signals occupying the frequencies above audio.
I can't understand why you kept saying switch. It sounds to me like a relay is clicking when you turn the tuning knob. ???
it’s crazy to think about all those tv and radio broadcasts out there in space, trickling in and trickling out of existence as they fly by whatever’s out there listening.
I really enjoyed the video, I’ve never received a recommendation for you before.
My issue is that I was JUST telling my wife (last night) about how Muzak, in stores and even literal elevator music, was broadcast on the “standard” FM band, but they used a sub-carrier wave to hide it from ppl who didn’t pay...
Wow, I have been finding these radios stuffed away in the back of old banks wiring rooms.
Love the Sigmund Freud Action Figure in the back - hilarious!
If it fell down would it be a Freudian slip?
If its not one thing its your mother.....
I worked for Microsoft Research on the SPOT project. We were leasing SCA bandwidth to broadcast digital signals to our watches. en.wikipedia.org/wiki/Smart_Personal_Objects_Technology to read about it.
If I'm not mistaken, SCA is now used for HD Radio broadcasts. If a radio station in your area was using that frequency range, you might hear some sort of digital encryption of their HD2/HD3 broadcasts. Not sure what that might sound like on an analog receiver.
Have you ever seen one of the pre-FM multiplex "stereo" tuners or receivers? They used AM-FM simulcasting to have the left channel on AM and the right on FM (or vise-versa) to get stereo. The AM sections of those tuners were wideband, capable of excellent fidelity since it was trying to match the FM performance. I have two, a Sherwood receiver and a Pilot tuner-preamp that were built for that system.
Never heard of this, listened with interest!
I remember riding to my friends place, he alway knew I was coming because the old Kawasaki triple would mess up his kitchen radio.
As a broadcast engineer, the SCAs are useful for transmitting satellite signals (sports,news,etc) to a main studio without using a bi-directional STL. (Just as one person mentioned sending transmitter data). This is very useful when you cannot put a C-band satellite dish (remember the BIG old dishes--that's what I'm talking about) at the studio location, but have ample room at the transmitter site. Thanks FRAN for documenting the history of subscription radio! Kinda missed the Fran's Lab intro, though. Keep up your excellent work!
One interesting use of SCA ("PM" as you called it, was a brand name) was at an AM/FM station I worked for. We had talk shows on the AM that were broadcast with a 7 second delay which made it impossible for the traffic reporter in the helicopter to get a "real time" intro from the show host. So, we fed the "pre-delay" AM program feed through one of the SCAs (each FM station was licensed for 2) of our FM station and put an SCA receiver in the aircraft. Worked like a charm. The other SCA was used for subscriptions to stores, restaurants and dental offices for background music.
That was fun! I built a bootleg SCA decoder back in the 70's when I was still in High School. It was based on a single 16pin DIP IC that did the heavy lifting with a few other passive components. It was fed by the MPX output of a Sony portable radio. I got it to work ok. BTW, I lived near Chicago, so there were several SCA signals available. Ya, it worked, but the fidelity was communication quality, like maybe 200-3500Hz? The novelty wore off pretty fast. I was more impressed when I assembled a stereo decoder at the same time! That was cool. Ran it off the same ole Sony portable radio! Had fun then.
Yeah I built one of those NE565 chip kit boards back then...later used it to decode the audio from the local pay TV station
Back in the day, studio DJs would talk to the transmitter site tech. on the sub carrier. WFCR
Yeah, we did that too. WYSO-FM
@@johncartwright6395 It's been over 40 years since I last listened, but aren't those the call letters for the station in Yellow Springs, Ohio? Listened in the late '70's- It was a Great radio station!
Thanks for your time and effort in making this!
Amazing ! It's nice to know that radio is alive and kicking.Your lecture brings back a lot of memories. You are amazing too. Thanks !
Thanks for bringing back memories, Fran. I was an engineer at WKBQ-FM in St. Louis, and (for a while) we carried PRN on our subcarrier.
Hi Fran! Great video... There's a fascinating history behind FM. It actually existed long before WWII. FM was invented at Columbia University in the 1920's using the 50 MHz band. In 1945 at the behest of David Sarnoff (the CEO of RCA) the FCC reallocated the FM band to the present day 88-108 MHz. This was done intentionally to put Armstrong and the Yankee Network out of business to protect RCA's AM empire. So much for backward compatibility... In the early 1960's, there were competing FM stereo systems. The two under consideration were the Crosby system and the GE/Zenith system. The Crosby system was simpler (i.e. easier to demodulate) and had better sound quality with much lower noise but unfortunately used more bandwidth. The GE/Zenith system was more complicated, and had much more noise but used less bandwidth. Unfortunately the FCC caved in to pressure from GE and Zenith as well as from broadcasters looking to make money renting bandwidth on their carriers and so the GE/Zenith system was selected. Less bandwidth for the stereo broadcast meant that more bandwidth was available for other subcarriers. So, the FM stereo we grew up listening to could have been quite a bit better, especially if the signal was weak had the Crosby system been selected. Oh well... Subcarrier stations are really not used anymore today. Services like Muzak are delivered over the internet now. The history of radio is almost as interesting as the electronics!
SMB FM bandwidth is different than AM bandwidth. Sub carriers do not use more bandwidth(surprise) . The bandwidth corresponds to the volume of the audio. The max allowed for FM is 200 kHz at full volume. Sub carriers are not RF but are AF, they are mixed in with the audio source. The transmitter sees audio from (guessing here) 20 Hz to at least 80 KHz when sub carrier is used.
You are "kind of" right. The max bandwidth of the FM channel is actually 150Khz with a 25 Khz "guard band" on the lower side and another on the upper side. The center frequency is the carrier frequency. Of course the next station on the dial will have the same guard bands so the very edges of deviation will be 50 Khz apart from the edge of the next channel. So, that's 200Khz total - but it's not all deviation. This includes baseband mono (L+R) audio of 50-15,000hz (it never went down to 20), a "pilot" tone for the stereo subcarrier at 19Khz, that was doubled to 38Khz in the receiver which was the subcarrier for the stereo "difference" information (baseband audio was L+R to be compatible with mono receivers - the difference signal at 38Khz was also 50-15,000hz but was the L-R signal), and then the SCA sources used the subcarriers in the band of 70-90Khz. The SCA signals were mono - and I "think" band limited to 5khz (AM radio or telephone quality but "no static at all"). With the SCA signals being band limited, you could actually get two SCA signals in there if one was at 70Khz (+/-5khz) and the other at 90Khz (+/-5Khz). The area between 75-85Khz would be the "guard band" between the subcarriers! Most likely this is why Fran's receiver has two slugs on the decoder board... All of these signals (yes "audio" signals - just many higher than you can hear) added together could have a total deviation of +/- 75Khz. Deviation more than this +/-75Khz (150Khz total) would not make anything "louder", in fact, you wouldn't hear the signal AT ALL as it would be out of the passband of the discriminator circuit and by FM's "capture effect", the radio would try to tune in the next closest signal on that frequency. The baseband signal was brickwall LP filtered at 15Khz as to not interfere with the 19Khz pilot tone - and the pilot tone (sine) came from the transmitter so that the receiver would be phase locked to it! :-) The low end of the baseband audio was limited to 50 hz as in the old days they would record a sinewave tone of 25 hz at the end of reel-to-reel tapes. A decoder would sense this and turn the next R-R machine on! (Pure genius, eh?) They filtered that control tone out so as not to blow up cheap speakers! ;-)
@@hotpeppersrcool I didn't even know that there is or used to be a 25 hertz tone on FM broadcasts that could control reel-to-reel recorders....I'm thinking it was used with a bank of recorders used to log and record an entire station's transmitted output in case of complaints such as "Hold your wee for a Wii".
Worked on many Muzak SCA tuners back in the mid 80's under contract with Muzak. There was also a reading service for the blind which I still believe is in use. Muzak switched to satellite receivers in the 90's. When I worked at WOSU Radio in the late 60's we would broadcast the Ohio Nursing Network using SCA on WOSU FM. Garmin also uses FM subcarriers today for traffic updates for their GPS units. Thanks for the video.
I am thrilled that you recommended “Empire of the Air” and spoke of Edwin Howard Armstrong. The film is a two hour documentary by Ken Burns based on the book “Empire of the Air: The Men Who Made Radio” by Tom Lewis. Both are exceedingly excellent and a must read/watch for anyone interested in broadcasting, radio, electronics, American popular culture or American history. Edwin Howard Armstrong is one of the greatest inventors who ever lived and his inventions can easily stand next to those of Edison, Tesla, Goddard, Turing or the Wrights. Yet he’s nearly unknown. With David Sarnoff and Lee DeForest added into the mix, this true story becomes a whirlwind drama in real life. And it’s our American “radio” history!
A Sigmund Freud Action Figure.... there has to be a joke there somewhere- or is it just in my subconscious?!
Sometimes an action figure is just an action figure.
Verrrry Interesting Liebchen.
Bittet es dich, es über deine Mutter zu erzählen?
Pay attention, you might learn something.
Sometimes a toy doll is just a toy doll...
5:00 Nice Steely Dan Reference Fran!! Great tune.
I worked as a contractor at PRN from '84-'86 when the facilities moved from Columbus Circle to Stamford CT. I also worked for WDJF-FM from '79-'83 which carried PRN on its subcarrier.
I haven't seen one of those radios in a long time. There were very few of those sets in the inventory. I think the hour meter was to allow certain physicians to log their continuing education credits. They may have had other uses as determined by the company's management or marketing teams.
The two-knob PRN receivers were supplied for FREE to physicians. Each receiver was tuned to a single frequency, which was how we sorted them. When a request came in we looked up the location and determined which broadcaster we were leasing the subcarrier from. Then a radio which was pre-tuned to that stations frequency was shipped out. The physician plugged it in and turned it on.
We'd regularly get angry calls from doctors who moved their practices from one market to another, and they'd be upset that their radio stopped working or on rare occasions was playing unrelated content.
The programming for PRN consisted of a 60 minute 'show' created daily on a continuous loop. The program started at 12:00am and ran on a set or four redundant 'cart' players. Think of an '8 track tape' but almost foot square!
The programs consisted of interviews, news articles, pharmacy reports, international reports, journal pieces, and of course commercials. Someone had to pay the bills. There was a team of reporters & interviewers, and reporters and three fully equipped studios where they could conduct telephone or live interviews. Every producer had their own editing machine; 1/4" open reel deck, headphones, white grease pencils, splice block, razor blade, and tape dispenser!
Minnesota Public Radio was running SCA back in the 80s to deliver talking books for the blind. It was nice and I think it was delivered as a public service.
Fran is that one carecter still missing in big bang theory ^^
"Tatters of Jive and Boogie Woogie"? I think I've found my next album title.
It's called Rap and Hip Hop these days, lol.
DeForest was the penultimate curmudgeon. At the beginning of the quote I thought he might be referring to *advertising* -- I would have been all on board with that.
Absolutely new to the channel, love the stories and explanations for the functionality behind all of this stuff! I have a bit of background in sound synthesis, so I get excited whenever I hear about FM, even though it's used in a completely different context lol
Fascinating, I had no idea this existed. I share your sadness and lament in regards to older broadcasts and formats that just....Went away. When I first saw the title of this video, I thought this was going to be about "HD Radio", which was a big-deal-thing a few years ago but didn't seem to take off, whereas Satellite Radio was dominant. Radio has a special place in my heart, there are certainly times I miss the physical dial, but yet, totally take for granted the digital format, quality, and speed/convenience of just pushing a button and instantly going from one end of the band to the other, etc. Much like the HDTV revolution and the ending of analog broadcast. I feel like we all lost a little of something there.
I was about to say "Commercial free broadcasting for a fee? We don't have that in your superior imperial masters..."
...then I remembered, Americans don't need a licence to operate a TV like we do...
FM subcarrier broadcasters is something I never heard of. I'd have thought the BBC would have tried it, maybe broadcasting surround sound on Radio 3 or something to be listened alongside the regular FM broadcast.
In the UK, we have the same band for FM radio, apparently the USSR and Japan used different bands for FM. In the olden days we referred to it as VHF.
The BBC used to have simulcasts betweeen FM and Medium Wave. They stopped that in the 1990s, held on to their FM broadcasts and let commercial stations take their former MW frequencies.
Now they simulcast with DAB. Though Radio 4 apparently still has their Long Wave broadcast (which also simulcasts with DAB)
Also, backward compatibility wasn't thing with TV in the UK. Black and white TV was in the 405 A standard on the VHF band. Colour TV was PAL in 625 lines on UHF only.
Now, nothing's backwards compatible, even DAB has made non backwards compatible changes (DAB to DAB+) if only DRM radio (Digital Radio Mondiale) took off, perhaps they should have picked a better name...
You're forgetting that we (the UK) had black and white TV on 625 lines, UHF years before colour came along and so the colour system when it was introduced had to be compatible with it. This was done in a similar way to the FM stereo method by transmitting a total brightness signal (called luminance) which the old sets used and separate colour difference signals.
black and white 625 line service was only on BBC2 when it first started AFAIK, I'm not entirely sure, but when BBC2 started in 625 line black and white, the UK had already decided to use PAL colour, as opposed to NTSC or SECAM.
It's still backwards compatible with B&W. There were many 625 line B&W sets. We had one in school to watch the childrens' programmes back in the early 1970s. I still have a black and white portable set, somewhere in the attic. It still worked last time I tried it but that was before the 625 line analogue TV was discontinued. I'd have to use it with a DVB receiver with an RF modulator now!
I think I read somewhere that ntsc colour was added to the 405 signal in the London area, wasn't it?
"I think I read somewhere that ntsc colour was added to the 405 signal in the London area, wasn't it?"
Only as a test transmission, it was those tests that apparently made them decide on PAL.
I remember seeing plans for these in Radio Electronics magazine.
John Possum I recall seeing several articles over the years about building subcarrer converters. I wonder if you might be able to build a converter in GNU radio?
Radio Shack sold the kits . I remember the beautiful music station in Pittsburgh also had a sub carrier. You would know because there was a pause before the commercial came on the DJ was putting another song on while the commercial was playing. You had to have two FM radios playing with one being the sca music service. If I'm not mistaking the rest of the music line up was identical except during a commercial frame. The station knew which song was as long as the commercial. It was interesting. I still have my radio reading service box but it quit working. I don't know if the station still offers the radio reading service. I was eligible to receive the service because I was dyslexic.they probably are on the internet now like all other services.
Great video Fran! I love these old SCA radios; the ones from COMPOL (sometimes labeled CIRRI) were very high quality with a nice solid oak cabinet and a simple power/volume knob. I got mine to make a single-frequency FM receiver - plays my local classical station all day. The mod was easy and the former owner of the company still had a stock of crystals and sent some tips on how to do the mod. I have the radio in my lab at work, and now there is no arguing about what to listen to.
Absolutely charming!!! And when I saw your Laura LP on display, I just had to SMILE!
Hi Fran, very interesting video thanks. I remember listening to several sub-carriers in my area back in the 90's using a Ramsey Electronics kit I think it was that I installed into an old FM receiver I had. Also, there is a very easy way to do it if you have both and FM receiver and a good quality SW receiver that will tune down into the below 100 Khz range, can't remember for sure how I did it but I think I took the audio output of the FM headphone jack and ran that through a .01 cap into the antenna jack of the SW radio and tune to the sub-carrier freq of whatever they were, like 67 khz or 90 khz or something, there were a few frequencies being used. It worked great and I could tune them in that way, it was published in a Monitoring Times magazine issue back in the day I think on how to do that. Been a while since I did that but I think that was correct. It was very simple I know. Keep up the great videos, I enjoy very much!
Simple yet clever modification, nice!
Some radios have filters that won't pass the high frequency to the speaker, but those ones are more expensive. A cheapo radio will pass it through because the speaker can't vibrate that fast and your ears wouldn't hear it even if it could.
The local sandwich shop used to give away sub-carriers if you bought more than one sandwich.
As a big supporter of sandwiches,
I have carried more than a few subs in my time.
I know it's a pun and all, but we had a burger joint giving out free pagers back in the day when thoey were on their way out and cellphones were on their way in
Awesome historic and valuable information! I love your commentaries.
Hi Fran. I don’t remember PRN the way that you described it. Rather than a commercial free music broadcast for doctor’s waiting rooms, it was actually educational programming geared toward physicians and included commercial advertising for pharmaceuticals. I do not recall the counter on the back of the radio but my guess was that it was used to tally the amount of time spent listening to the continuing education content in order to claim credit toward a yearly certificate of completion.
Addendum to the comment by Max Zomboni:
As a pre-med student in the 1970s I built an SCA adapter and hooked it to my stereo (you had to tap the signal from the detector, prior to the de-emphasis network). I used to listen to PRN, which was completely separate from Muzak.
These were the (better) days when it was illegal to advertise prescription drugs to the public. As Max said, PRN radios were given free to any MD who requested one. The purpose was to provide a private channel to MDs that drug companies could use to hawk drugs. They would broadcast medical news and other content of interest to MDs and intersperse prescription drug ads which were just as absurd as the ones we now have on network TV. The demise of PRN was due to the legalization of ads to the public advising people to tell their doctor how to manage their diabetes, hypercoagulation, and cancer chemotherapy.
Capitalism belongs in medicine the way airplanes belong in skyscrapers, which is not at all.
Hi Fran, The chronometer resolution isn't necessarily an indication of the billing rate.
The chronometer they used might have been the best compromise of form, fit, function, reliability, cost, availability, etc. that PRN could get. Perhaps PRN charged a flat rate for the first 0-100 hours and didn't pay much attention to the first number ring.
I imagine the most practical use of the first number ring would likely be for the support person who shows up to take the meter reading. They could quickly and easily confirm that the counter was still operational (not bypassed for cheating the system).
The counter might have been used to report back the number of hours listened to on average, or per quarter or half year etc. Not for billing per say, but to tell their advertisers how much listening was actually being consumed. As I'm sure most offices would turn the radio off at the end of the day.Thus it was a pretty accurate measurement of listenership.
I built an Eico FM Tuner kit in 1962, with a
green tuning eye, with a jack for a multi-plex
adapter add on. WQXR in New York City,
first tested Stereo, with one channel on their
FM frequency, and the other channel on their
AM frequency, in the early 1960's.
Years ago I had an SCA adapter sold by Dr.
Bruce Elving, PHD, now deceased, to add to
the multiplex jack of a radio to receive SCA.
Ray, W2CH, WPE2FXT and KBG7077.
What took me so long to discover you! Fantastic! You've earned yourself a subscriber madame!
it would be cool to hear about the two versions of AM stereo and RDS
RDS I second that.
AM stereo systems in use are CQUAM (Known to be used in Australia and Japan), ISB and Comb Stereo (what RNEI, TIAMS and some songs on KBC have, it's a newer system for stereo AM over mono transmitter I had a part in making, give it a search!
My friend actually broadcasts and streams AM stereo from his radio station using CQUAM. It's quite amazing actually. Search I -1430 WION. The stream you hear IS AM stereo is streamed out from a Carver AM stereo equipped receiver.
You were talking about arcing causing interference on AM radio. I've heard that's how utility company used to find a broken power line was by driving the truck next to the power lines with the AM radio tuned to a weak station.
HAMs still do this as a combination game / public service / enlightened self-interest thing. Look up RFI Fox Hunting - here's the ARRL's how-to video: th-cam.com/video/aT-EFcZ7hbA/w-d-xo.html
Failing insulators and jumpers on high-voltage lines can wipe out a significant portion of the SW bands for tens to hundreds of miles around the faulty equipment before they reach the point of being an immediate danger to people or property.
By the same token, cable companies used to put a highly annoying signal around 108Mhz to find the breaks in their lines. If you are old enough, you might remember that in the 80's we also had "cable FM". Usually your standard channels but on unused channels the would put the stereo audio tracks for HBO and other movie channels. Movies were in stereo by then, but most people did not have stereo TV's and it would also sound much better on your stereo speakers.
We can still do that; Realistic made an AM/FM radio that could do AM on the FM band, and you remove the loopstick and whip, add coax to a little measuring-tape Yagi. Swing it around to point to the loudest source, call the power company to come sledge-hammer their pole (don't you do it for them!) and verify they need to replace/repair an insulator.
That problem made 40m phone difficult for the W6KA/W6UE/W6VIO clubs at ARRL Field Day last year; sure enough, one of our members found it and got Edison to eventually come fix it.
VHF/UHF Fox Hunting (or Foxtailing) have annual international competitions, and they combine low HF on 80m for the challenge. Have a look at www.homingin.com for more.
@@pbarnrob 2 meters as well. You had to find the transmitter, you made your own direction finder. I guess it helps the FCC police the ham bands. Ham operators can report illegal activity to keep Ham bands enjoyable for law abiding hams. CB radio is a disaster of illegal activity.i won't go there.
A particularly awesome episode here, Fran! Kickin' ass and takin' names!
I just scanned the SCA services, I could only find digital services, no analog signals here in the Dallas-Fort Worth area. My tuner consists of my FM/AM receiver with a MUX output, hooked into a VLF converter, which is then plugged into my communications receiver that so I can scan the FM stations and all of the available SCA broadcasts. By the way, the FCC states that it is illegal to have a radio that can scan the SCA channels! SCA is being used for the HD Radio channels in digital format, something you may do a video on in the future. I am a fan of HD Radio, the quality is excellent and it is free! Thank you Fran, for your great videos.
PS: My FM/AM receiver is a National Panasonic SS-7800 from the early 70's, made for 4 channel reception, apparently Panasonic hoped back then that SCA was going to 4 channel use. Hence, the MUX output.
We in the Uk still pay a fee for an ad-free station its called the bbc
who cares about bbc it's garbage anyways
LM357 would be the chip. Built a few SCA decoders over the years to pirate the subcarriers.
Radio shack used to sell LM565 chips with a crappy SCA tuner schematic in the 1980s.
One of your best Fran! Thanks for this information which was news to me.
Thanks again for sharing. This is something I was completely unaware of.
if you don't want to muck around inside that radio you can use various techniques with an rtlsdr ($10 software defined radio dongle) to receive fm subcarrier broadcasts. see web.archive.org/web/20160304171452/rtl-sdr.better-than.tv/?page_id=193 for a guide on how to do this relatively easily. there is also a bit more involved method using a gnuradio set up for the usrp receiver but it can be easily adapted to use an rtlsdr as a receiver github.com/gnuradio/gnuradio/blob/master/gr-uhd/examples/python/usrp_wfm_rcv_sca.py
Fran just marry me, because there is too much bad stock out there.
its a man...
Some stations used this for college football networks.
The football network would have stations pick up the game on the dedicated sub channel and simulcast the games on the main FM station.
I worked for Muzak.
We used subchannels to the location received on a fixed channel non tunable receiver and out to an amp and speakers.
The service was sold as a flat monthly fee.
I'm an amateur radio enthusiast, and never heard of this before. Awesome! Thanks for sharing.
As a Radio collector curator , I find your work fascinating . Thank You :) QC
I'm viewing this 3 years after you posted it, but you would have been really amazed at the early "analog" satellite signals (think pre-1990s), some transponders had many dozen subcarriers on them
Fascinating,. I build a few of these decoders back in the day. I even installed one inside of my old Pioneer KP500 car stereo. I actually liked listening to the "elevator" music on some channels. I found that one easy way that you could hear an SCA, was if you had a Wideband scanner/reciever; Set the Mode to Narrow FM. Then tune it just a bit above a strong FM Broadcast signal by 65 - 75 KHz. There is/was a similar subcarrier system on analog TV audio. One for for the SAP, but there was also this thing called, Pro Channel at 102 KHz.
what a great channel. you started talking about am demodulation and all the sudden i was off tinkering, and long story short i now know new things about hilbert shifters and instantaneous amplitude
Sorry there weren't any SCA broadcasts for you to tune in for us, Fran! I built an SCA decoder from a kit back in the mid-ninties when I was a bench tech at WEVD-AM 1050 in NYC. I used it at home, but I built it at the station when there was down time. Cool stuff. Thanks for sharing.
About 35 years ago while living in Sydney AU I built a Subcarrier FM kit which interconnected to an FM radio as I heard stations were running trial broadcasts anyway I received a couple of these broadcasts I had completely forgotten all about this until your TH-cam clip come up
It's great to see so many kindred spirits here!
I, too was a pre-med student in the early 1970s who spent a lot of time with electronics hobby projects (and music). I read the article in Popular Electronics using a NE565 PLL chip to make an SCA receiver and built one. Growing up in the Chicago suburbs, I found the PRN on one of the (then) three classical music stations: WEFM at 99.5MHz. We also had "books for the blind" on another station, Chinese restaurant music, and a digital signal that had stock market information (so I was told).
Later on, after I didn't get in medical school and entered Engineering school, I built another one using a newer IC (SGS TCA3089) that was basically an FM radio on a chip.
PRN in those days was entirely made up of medical news and ads for prescription drugs. I think there was a single hour of content that was looped over and over all day.
Through lack of adequate filtering of the SCA adapter input, I heard a lot of leakage from the main channel. Not so bad when it was classical music, but when they switched formats and became a rock station, the high hat cymbal "notes" were a constant annoyance.
I added my SCA adapters to two of my FM tuners, one an old KLH tuner, the other, a Heathkit digital FM tuner I built. THen life intervened, I got an engineering job, and didn't have time to sit and listen to SCA anymore. It was a lot of fun back in the day, and I'm glad I played with it!
Very Interesting Fran - I have recently been playing around with FM baseband demodulation in software, and you've inspired me to add some code to extract the subcarriers. I've noticed that most commercial FM stations in Australia have RDS at +57khz (for text transmission), but I can see (from the waterfall display in my SDR software) that others do indeed have analog stuff up there - I'm interested to find out what it is !
There’s something enchanting about the static crackles, fading and distant feel of AM, particularly SW. Some of us started in electronics because of it. Oh, don’t forget the oscillator whine in superhet versions of AM. In this particular case, why not build a TV broadcast to FM band downconverter. You will defined be able to detect the voice on your PRN.
I have 2 books by Zenith discussing their proposed FM stereo system (which was adopted by the FCC). One of the texts suggests that SCA subscription services were already in use for some time prior to the introduction of FM stereo and that a feature of their stereo multiplex system was that it could coexist with the existing subscription services stations had at the time. It also suggested that at that time many FM stations needed the subscription revenues to survive.
I have a 70's vintage SCA adapter kit (though it is missing the IC so I can't build it) the instructions explain that it is designed to connect to the output of the FM detector in a normal FM radio and it will decode the SCA transmissions from that. Meaning that like an FM stereo MPX adapter the SCA adapter once aligned did not require any tuning (tuning was strictly the job of the normal FM dial of the radio). Odds are by adjusting those slugs on the SCA add on board in that Sony you have messed up the SCA adapter alignment likely making it incapable of tuning any SCA transmissions until it is realigned correctly.
If my understanding of what I have read is correct both FM MPX stereo and SCA were ultrasonic audio carriers modulated by normal audio. MPX being a 19KHz pilot tone and 32KHz carrier AM modulated by the difference between L and R channels (that would be added and subtracted from the L+R mono FM audio to create stereo). Where SCA was a 67KHz and or 100KHz (what I've read wasn't very clear on freq) carrier that was FM modulated.
One of the sub-carriers I remember was Muszak Inc. Or the famous elevator music we all know and loved. This was also supplied on leased phone lines if no station was available.
Where I live there used to be a radio station that transmitted a SCA signal for supermarket music. They used a dedicated receiver/amplifier that was tuned only to that frequency. In addition to providing music, they used the other channel for conference calling.