Roman, in the pre-internet stream days, SCA's were used for multiple uses by FM broadcasters. Muzak offered its services using SCA, either on 67 kHz or 92 kHz sections of a signal. Where I live, the Illinois Farm Bureau had a 24 hour stream of ag news for those who subscribed to a fixed-tuned radio that carried the program, as was the Physicians Radio Network for doctors. Reading services for the blind also use SCA audio throughout the USA. There are also data services. There is a Minnesota connection to this--Bruce Elving printed an FM Atlas of stations with detailed technical specs on US radio stations, along with their SCA's. He also modified radios to receive them and sold them (I have two of them). Bruce died in 2011--here is his wikipedia entry: en.wikipedia.org/wiki/Bruce_Elving
Hopefully you’re still able to hear something with your radios. I was one of two technicians that Bruce had hired on a regular basis during the 90s and 00s to modify consumer type AM/FM radios to play the subcarriers. A lot of Bruce’s customers were those who were wanting to tune in the Radio Talking Book. Unfortunately in 2013, the subcarriers were shut off in the state of Minnesota and the Radio Taking Book was switched to encrypted over IBOC.
The radios I have still work. Most of the SCA's were shut down, but our Radio Information Service/Minds Eye reading service still uses 67 kHz SCA even over an IBOC station. The service is hoping to drop their SCA over time, as their internet stream and on-demand services are becoming more prominent. SCA's are also used for 'talkback' between on-air people and remotes.@@LiquidRadio
@@LiquidRadio I found out today (11/22/2024) that NPR station KCUR 89.3FM in Kansas City, MO, still has a 67khz SCA subcarrier that is carrying some kind of "Reading for the Blind" service.
Hi Roman here is the answer to your mystery AM radio signal hidden within the FM stereo signal. What you are receiving is a backup audio signal of the AM radio station that the FM station is broadcasting as a backup signal from the studios out to the AM transmitter site. I have been in radio broadcasting for over 35 years and have used this method a number of times especially in the days before internet access existed and audio streaming was only a dream. Back then there was only a few methods to get your audio from the studio out to a transmitter site. One way was using an RF link, typically in the 450MHz or 950MHz bands, called an STL (Studio to Transmitter Link) the other was using good old copper phone lines that had been bandwidth widened to carry audio up to 15kHz . (BTW if you scan the 450MHz and 950MHz using your SDR you will likely still find some of your local stations' STL signals still in use and using either FM mono (called discrete channel where the left and right audio channels are broadcast on different frequencies) or they may be using stereo FM (called composite channel, where the multiplexed output is just passed straight through to the FM transmitter) In my case, one of my AM stations could not get a line of sight connection for an RF link and could only get one 7.5kHz phone line out to the transmitter site because there was about 25 miles of copper phone lines and 6 amplifiers between the studio and the transmitter . Phone lines (especially in my area) were often dug up by someone who went crazy with a backhoe or one of the amplifiers located at the telephone company CO (central office) would fail. In either case, the AM radio station could be off-air for hours, or sometimes days until someone from the telephone company figured out where the failure was and repaired it . To provide some kind of back up, I used the 67kHz SCA channel to broadcast our AM programming through our FM transmitter as a backup link to the AM transmitter site. Because it was on the SCA channel the average radio listener would never even know it was there. The setup at the transmitter site was simply a high gain FM antenna and a tuned SCA receiver connected audio processing and EQ's to make it sound better. It wasn't a perfect solution but it was better than being off the air. Hope this helps to clear up the mystery for you.
There is no longer any sca signals in northern ohio, I used to get a few sca channels from a few stations, a local public broadcasting station used to have signal on 67 Khan and 92 Khan, those signals today are no longer being broadcast. Looks like everything has gone to satellite.
I'm pretty sure like I said before this is probably a way to get KNSP's audio over to FM in case of an emergency event. I'm sure there's probably a way to switch the audio to the main FM carrier, but I don't know. KNSP at one time was probably the home for News during an emergency, and probably was the easiest way they could find to do it without interrupting the main FM signal. KSCR in Benson for example uses a link between the studio of KBMO to the studio of KSCR to relay audio in case of an emergency event. Only issue...for whatever reason the AM doesn't get muted fully and you can hear the AM under the FM at times. I was told by a friend who formerly worked there that it seemed there was no way to mute the AM's audio.
Probably the single best way I could possibly think of to get KNSP-AM on the same station as KKWS-FM is to simulcast KNSP on one of KKWS's HD Radio subchannels since I could clearly see the HD Radio carrier on the spectrum analysis of KKWS's signal. Also, I can't see any point in using SCA with HD Radio on the rise.
Haven't watch the entire video yet. But I'm going to make a guess that maybe that is there AM signal so that in case of an emergency, KKWS can easily switch to the AM simulcast. I don't know, but that's my guess
You are likely receiving a 67 kHz SCA subcarrier, and your studio to transmitter idea is likely correct. If the AM transmitter is colocated with the FM and their 950 MHz link supports it, thet could use a subcarrier the would be filtered out by the low pass filter ahead of the FM transmitter. I once used a 185 kHz subcarrier for the command link of the remote control system. What might be going on is that the AM transmitter is not colocated with the FM and they are receiving the FM off air at the AM site and demodulating the 67 kHz to feed the AM transmitter.
There stations are all Over the metro most new vehicles do the split channels receiving so you can hear 92.5 1 and 92.5 2 might be news or rock 92.5 3 more news
That's HD radio, which is digital, and is a sideband next to the standard FM broadcast incase you didn't know. SCA is actually inside of the main FM broadcast and analog
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Roman, in the pre-internet stream days, SCA's were used for multiple uses by FM broadcasters. Muzak offered its services using SCA, either on 67 kHz or 92 kHz sections of a signal. Where I live, the Illinois Farm Bureau had a 24 hour stream of ag news for those who subscribed to a fixed-tuned radio that carried the program, as was the Physicians Radio Network for doctors. Reading services for the blind also use SCA audio throughout the USA. There are also data services.
There is a Minnesota connection to this--Bruce Elving printed an FM Atlas of stations with detailed technical specs on US radio stations, along with their SCA's. He also modified radios to receive them and sold them (I have two of them). Bruce died in 2011--here is his wikipedia entry: en.wikipedia.org/wiki/Bruce_Elving
Hopefully you’re still able to hear something with your radios. I was one of two technicians that Bruce had hired on a regular basis during the 90s and 00s to modify consumer type AM/FM radios to play the subcarriers. A lot of Bruce’s customers were those who were wanting to tune in the Radio Talking Book. Unfortunately in 2013, the subcarriers were shut off in the state of Minnesota and the Radio Taking Book was switched to encrypted over IBOC.
The radios I have still work. Most of the SCA's were shut down, but our Radio Information Service/Minds Eye reading service still uses 67 kHz SCA even over an IBOC station. The service is hoping to drop their SCA over time, as their internet stream and on-demand services are becoming more prominent. SCA's are also used for 'talkback' between on-air people and remotes.@@LiquidRadio
@@LiquidRadio I found out today (11/22/2024) that NPR station KCUR 89.3FM in Kansas City, MO, still has a 67khz SCA subcarrier that is carrying some kind of "Reading for the Blind" service.
Another radio mystery solved. Good job, Detective Roman.
this is pretty cool! I'm intrigued
Hi Roman here is the answer to your mystery AM radio signal hidden within the FM stereo signal.
What you are receiving is a backup audio signal of the AM radio station that the FM station is broadcasting as a backup signal from the studios out to the AM transmitter site. I have been in radio broadcasting for over 35 years and have used this method a number of times especially in the days before internet access existed and audio streaming was only a dream. Back then there was only a few methods to get your audio from the studio out to a transmitter site. One way was using an RF link, typically in the 450MHz or 950MHz bands, called an STL (Studio to Transmitter Link) the other was using good old copper phone lines that had been bandwidth widened to carry audio up to 15kHz . (BTW if you scan the 450MHz and 950MHz using your SDR you will likely still find some of your local stations' STL signals still in use and using either FM mono (called discrete channel where the left and right audio channels are broadcast on different frequencies) or they may be using stereo FM (called composite channel, where the multiplexed output is just passed straight through to the FM transmitter)
In my case, one of my AM stations could not get a line of sight connection for an RF link and could only get one 7.5kHz phone line out to the transmitter site because there was about 25 miles of copper phone lines and 6 amplifiers between the studio and the transmitter . Phone lines (especially in my area) were often dug up by someone who went crazy with a backhoe or one of the amplifiers located at the telephone company CO (central office) would fail. In either case, the AM radio station could be off-air for hours, or sometimes days until someone from the telephone company figured out where the failure was and repaired it . To provide some kind of back up, I used the 67kHz SCA channel to broadcast our AM programming through our FM transmitter as a backup link to the AM transmitter site. Because it was on the SCA channel the average radio listener would never even know it was there.
The setup at the transmitter site was simply a high gain FM antenna and a tuned SCA receiver connected audio processing and EQ's to make it sound better. It wasn't a perfect solution but it was better than being off the air. Hope this helps to clear up the mystery for you.
I'm not Roman, but this is pretty darn cool. Thanks for sharing! SCA is probably the favorite thing I've found when playing around with SDR.
There is no longer any sca signals in northern ohio, I used to get a few sca channels from a few stations, a local public broadcasting station used to have signal on 67 Khan and 92 Khan, those signals today are no longer being broadcast. Looks like everything has gone to satellite.
Can you link your updated script?
1:34 “Minnesota’s Classic Rock Station 92.5 FM”
Really? Why not “Minnesota’s Classic Rock Station 92 KQRS”
Cumulus sometimes 🤦♂️
I'm pretty sure like I said before this is probably a way to get KNSP's audio over to FM in case of an emergency event. I'm sure there's probably a way to switch the audio to the main FM carrier, but I don't know. KNSP at one time was probably the home for News during an emergency, and probably was the easiest way they could find to do it without interrupting the main FM signal. KSCR in Benson for example uses a link between the studio of KBMO to the studio of KSCR to relay audio in case of an emergency event. Only issue...for whatever reason the AM doesn't get muted fully and you can hear the AM under the FM at times. I was told by a friend who formerly worked there that it seemed there was no way to mute the AM's audio.
Probably the single best way I could possibly think of to get KNSP-AM on the same station as KKWS-FM is to simulcast KNSP on one of KKWS's HD Radio subchannels since I could clearly see the HD Radio carrier on the spectrum analysis of KKWS's signal. Also, I can't see any point in using SCA with HD Radio on the rise.
Haven't watch the entire video yet. But I'm going to make a guess that maybe that is there AM signal so that in case of an emergency, KKWS can easily switch to the AM simulcast. I don't know, but that's my guess
You are likely receiving a 67 kHz SCA subcarrier, and your studio to transmitter idea is likely correct. If the AM transmitter is colocated with the FM and their 950 MHz link supports it, thet could use a subcarrier the would be filtered out by the low pass filter ahead of the FM transmitter. I once used a 185 kHz subcarrier for the command link of the remote control system. What might be going on is that the AM transmitter is not colocated with the FM and they are receiving the FM off air at the AM site and demodulating the 67 kHz to feed the AM transmitter.
Did the IQ file ever uploaded?
There stations are all
Over the metro most new vehicles do the split channels receiving so you can hear 92.5 1 and 92.5 2 might be news or rock 92.5 3 more news
It’s basically similar to how the local over the air tv channels are now 11-1 11-2 11-3
That's HD radio, which is digital, and is a sideband next to the standard FM broadcast incase you didn't know. SCA is actually inside of the main FM broadcast and analog
great video!! check out my next few videos i plan to build fm stations with subcarrier audio signals