“BASIC PRINCIPLES OF FREQUENCY MODULATION” 1944 U.S. WAR DEPARTMENT FILM FM RADIO 86794
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- เผยแพร่เมื่อ 26 ก.พ. 2022
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Made during WWII by the War Department, this official training film describes what frequency modulation (FM) is and how to use it in reference to radio communications. It also provides the comparison between FM and AM radio as far as what advantages FM has over AM. Originally restricted, the film was released for public educational use in 1949. It opens with U.S. soldiers playing ping pong while listening to AM radio (:28). When one of the men begins to use an electric razor, the radio gets staticky and one of the men switches the radio to FM so they can still listen to the music clearly (1:02). FM was a major step forward in radio and as guests tuned into a radio programs now they were listening to what the microphone was picking up (1:24). AM radio had its drawbacks in the sense that whenever it was used for communication in the battlefield (2:06) it would pick up static which would mess with the signal. Tank tracks made reception near impossible (2:13) as well as a slew of other war materials and natural occurrences such as thunderstorms (2:25). FM was able to remove this issue (2:34) and the film turns to breaking down the proponents of AM radio (2:40). A diagram follows, pointing to the oscillator (2:49) which generated the carrier wave that is fed into the amplifier (2:57). At this point it carried no message and for AM, intelligence was pressed upon the wave through a microphone (3:13). The intelligence is converted into electrical energy which goes into the modulator (3:24) and is then amplified. The intelligence is radiated by the antenna (4:06). The process of amplifying the waves is depicted (4:41) as it moves through the IF Amplifier and then the demodulator (4:55) which changes the vibrations back into audio frequency (5:03). From here it enters a speaker and becomes sound again (5:14). AM worked well in perfect conditions (5:38) unless there were any electrical interferences. A demonstration follows where a lighting strike interferes with the wave (6:00) which makes the wave fuzzy and the intelligence indiscernible. The film shows the difference between AM and FM (7:22). AM carried the wave through increasing or decreasing the strength of the carrier whereas FM did the same job by changing the frequency of the carrier this way the static would only affect the amplitude and not the frequency (7:43). A few of the types of FM transmitters used by the army follow (7:59). The FM oscillator is broken down in diagram next (8:21) with the rest wave pointed to. Capacitor microphones could change AM to FM waves (9:01) and this was done by placing one parallel with the capacitor and the tank circuit (8:57). With this addition, the frequency now varied at an audio rate (9:41). A diagram follows pointing to a line which represents the rest frequency of the oscillator (11:14) and how it varies when sound is impressed on the capacitator mic (11:34). As example shows how the frequency affects the rate of change (11:43) as well as how the volume or loudness of the frequency determines the amount of deviation (13:13). Due to the potential of the deviation to interfere with other transmitters (13:26), the army set a maximum deviation of 40 kilocycles (13:32) on both sides of the rest frequency. Guard bands were also provided as there must be some sort of separation between the channels (14:10) and 10 kilocycles are allotted on either side. In addition to what the film has already shown, the army also used two other systems to get FM called radiance tube and phase modulation (15:04). There are three main differences between the AM and FM receivers and these are the band pass (15:40), the frequency modulation receiver (16:03) and the amplitude variations. A diagram of the AM receiver follows (16:33) and how these variations can be changed to turn it into an FM receiver including the addition of the limiter (16:57) and the discriminator (17:21). The limiter is broken down in diagram (18:00) and how it clips off any variations on the positive and negative portions of the wave (18:49). After the variations have been clipped off, the wave ends are squared and this leads to distortion of the signal (24:42). The plate circuit handles this problem by smoothing out any irregularities or sharp corners of the wave (24:49). A simplified diagram of the discriminator follows (25:23). The wave from the discriminator is fed into AF amplifiers and comes out of the speakers in the same way which an AM receiver does (27:57). This film concludes (28:19).
This film is part of the Periscope Film LLC archive, one of the largest historic military, transportation, and aviation stock footage collections in the USA. Entirely film backed, this material is available for licensing in 24p HD and 2k. For more information visit www.PeriscopeFilm.com
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Back in the 70's, when I was an A/V tech at a local community college, I used a 16mm copy of this film as a test reel when repairing Bell & Howell movie projectors. I watched it at my bench, countless times on a piece of 8.5 x 11 cardstock for a screen, learning about frequency modulation in the process. Years later I applied for and got my FCC GROL and thanks in part to this film I got through the FM questions without trouble. Never knew of Kent Smith except for this film until later I saw him in several movies. I couldn't look at him in a movie plot without thinking of his voice saying "the capacitance of the tank circuit affects the frequency of the oscillator". Thanks Periscope for preserving these valuable historic treasures.
Nice!
These old movies seem to be much better at explaining basic principles of complex topics. Check out the early GM films about differentials for a perfect example of this.
@@Kangaroojack1986 Dude, that GM film is awesome.
Thats beautiful, man. Thanks for sharing
70s, not 70's. Seventies, not seventie's.
These old videos are better than any college lecture I've ever attended
Just think of all the money you could have saved ! :)
I swear I'm learning more from these than anywhere else
I can say same for some ussr education videos.
That’s what I’m saying duddeeee. I find myself understanding better when I watch videos like these
I wish I could find a library with all those 1940's and 1950s education and military videos.
These old training films are so well explained that anyone could understand them. Kent Smith, the actor who is doing the narration and demonstration was in the late 1960s science fiction program, The Invaders. He played the multimillionaire government contractor who was sympathetic to the main character, played by David Thinnes, who financed him and gave him contacts in the US government.
I thought he looked familiar. I'll have to research if he guested on Perry Mason.
And it's not like basic understanding of AM/FM has changed. This video is every bit as relevant today as it was 80 years ago.
I strongly agree.
Ну вот и ему достойное место в истории развития радиосвязи подкинули. Дрочи дальше.
You got the names mixed up. Easy mistake. It was Roy Thinnes who played David Vincent. Thanks , I was trying to figure out why Kent Smith looked so familiar
The generation that changed the world. May rest in piece
All generations gave some contribution. Fourier and Laplace are also important people
I love the fact that he uses the term 'hashing up' or 'hash up' to refer to the introduction of a second pattern (noise, in this case) to the encoded / modulated "intelligence" signal.
The modern use of 'hashing' relates to the introduction of a second pattern -- usually an encryption code -- to modern digital intelligence. At heart, these two senses of "hashing" are identical, even while the carrier of intelligence is different.
I love it because most of the concepts and terminology of modern computer science actual _pre-dates_ computers themselves! The modern conception of using strings of 0s and 1s as carrier of information is just a re-envisioning of the early 20th century technology of analog electrical pulses or radio waves as a carrier of information.
Very cool!! 😀
This is amazing and you are amazing... Thank you!!! Love learning 😂😊👌♥️
How are they actually sending 1s and 0s? If you look at digital AUDIO its almost always an analog carrier wave, usually voltage. Where the voltage is read as a 1 or 0.
@@shroud1390 I don't know enough about the technical details to give you a complete answer, but I'll share what I know. There are many methods to modulate a radio signal to carry 1s and 0s. Amplitude modulation is probably the most familiar because it maps nicely onto that voltage modulation strategy you described. Instead of high/low voltage, the radio waves are "burst" in chunks of high or low amplitude. Even more simple is OOK modulation, meaning On-Off Keying, where the high-amplitude signal is literally switched on for 1s and off for 0s. (OOK is crappy because a string of 0s is just dead air, so the signal falls apart with even small noise.)
There is also frequency modulation that works exactly like the analog FM described in this old video. Instead of having smoothly-variable frequency modulation to carry an analog message, the frequency is "jerked" back and forth to represent only two distinct values. (I think that's how those FRS "walkie-talkie" radios work, but I'm not certain.)
There are several other modulation methods, like "side-shift modulation" and many others, but to be honest, I don't understand how any of that works.
Bluetooth and WiFi use some pretty amazing modulation methods that permit sustained high-bitrate throughput even with dozens of devices blasting away. "Frequency hopping" is a big part of the solution here. All of it is interesting, but I don't claim to understand how it works.
Yes, the more things change the more they stay the same & there is nothing new under the sun. As a tenured computer professor, I totally & completely validate your comment. I often think how funny it is that all the answers, all the technology has been here all along, it's us humans that had to catch up or realize it. Wonder what else is around that we don't see yet? Great comment @HogTie Champ and what a great name, too.
@@HogTieChamp It is very interesting and though I was tenured in Computer Science & taught the basics the science is still incredible and quite in-depth. Lovely, intelligent comment ...again!
At 3:24 the film has the MODulator and the AMPlifier functions reversed. The film's 'MOD' is the audio amplifier and the film's AMP is the modulator stage.
I noted this also. And there usually is an RF power amp after the modulator feeding the antenna.
No,.Per U.S. Army, the film is correct.......Back in those times, the Modulator block contained All the Audio amplification circuitry.....The Critical frequency stabilized Oscillator was physically Separated from the Rf Amplifier, which the Modulator is wired to.....
@@tomstrum6259 still, the modulated signal is over the amplifier
My dad ran FM repeater stations out of a tent all over Europe in WWII. He was in the 926th signal batn. Part of the 9th TAC.
Somewhere in the bowels of my house I have a circa 1941 book titled "Understanding Radio". It referred to FM as 'static-less radio' and essentially said it was revolutionary. Looking at FM today... indeed.
Nowadays, Commercial FM radio is full of more noise than ever!!
@@metalbill These days only old farts say Now-A-days 😆
Some things in the old days were simply just better, no questions asked, and these videos are one of them.
These are so well done because the stakes for failure to communicate vastly exceed the self-absorbtion of the speaker.
As a professional guitar player who uses a compressor (sometimes called a compressor/limiter), this is the best explanation I have seen for what it does. Compressors are used widely by individual musicians and in the recording studio in post-production to make a signal more crisp and clear and somehow fatter, fuller, and punchier. Unlike distortion, delay, reverb, etc., this effect is the hardest to understand or describe. Since I got my first compressor/limiter many years ago, it has been my desert island effect. More than overdrive or any other effect, I cannot go without it.
It's not that hard to understand.
@@morbidmanmusic he didn’t explain how the compressor works, just how it’s utilized by musicians. Which is useful for somebody who isn’t a musician, or a novice musician.
Unless you know what to listen for, the average person is not going to hear the difference that a compressor makes. But its very easy to hear what reverb, or distortion is, as was explained by the original poster.
He also didn’t say he was confused by it. Rather, he explained the ways he likes it, and why he uses it.
Your comment was only a few words, but it was chock-full of poor reading comprehension.
Your ego got in the way, for literally no reason
Can you play freebird
These old military educational videos are AWESOME!!!
Thanks @Chip Eckardt. Please consider subscribing or become a channel member!
Бесшабашны и бесполезны точнеее.
@@navizhunastye3756 isnt there a tide pod somewhere that needs eating ?
This film is easier to understand than anything I've seen on FM. Even now technically useful.
Ты принцип работы транзисторов в школе не изучал?? Пичалька...
3:50 I think an important thing that wasn't mentioned is why you need to modulate the wave.
Its like putting a message in a bottle and letting water waves carry it across the ocean, only that here the ocean is the oscillating wave (An electromagnetic wave of some specific frequency) and the bottle is the sound signal you are trying to send. The oscillating wave is the medium where we can put out message and it can then travel wherever we need it too (within a range).
They don't make them like that anymore - absolute gold!
I asked my physics teacher at university how a FM receiver works and he couldn't explain it...
This videos are gold, what a very good explanations! Thank you very much!!
They are way too bothered with theories and formulas to dedicate time to real life engineering
Can he screw in a light bulb or cut the grass. I personally know many lawyers who never had an original thought.
Kent Smith I have seen in many films, but what I will always remember are the two masterpieces 'Cat People' and 'The Spiral Staircase', flawless as always.
Say what you want about A.M. radio. When we were kids my dad gave us old transistor radios. I'd lie awake at night tuning in stations hundreds of miles away.
Both have pro and cons. In Taiwan,most people live in tall apartment blocks. So MW or AM is often very tricky to get signal due to multipath and interference. If you are out in the open AM or MW would work better because it doesn't rely on line of sight.
I studied AM and FM during my diploma of Radio electronic associate engineer back in 1979.
Did you work in that field after you graduated?
@Chris
Yes, i served in Pakistam television, worked on low and high power Transmitters, my specialisation was repairer and maintenance of power supplies and RF amplifiers.
FM Stereo came out later for commercial broadcast. I believe it is on the other side of the resonate freq. shown at the 26:00 area of the video. This gives the dual channel stereo sound. That's why your broadcast stations are so far apart in freq. as opposed to commercial AM broadcast.
FM stereo transmits the sum of both channels at the regular audio frequency but then the difference between them outside the standard audio range - the receiver also detects the difference and then subtracts that to recover the two separate left/right channels. The difference centres around 38KHz, which is inaudible to humans and so doesn't interfere with mono
That was cool. I was a radio guy in the Army 30 years ago, and believe it or not, some of the radios I worked on still had tubes.
I was a WCS radar tech in the Air Force 40+ years ago and the radar package I worked on was loaded with them.
Montgomery Ward (remember them?) was still selling tube-type televisions through 1974. They had a big sale in our local store to liquidate the last of their stock of them that year. All of their models from 1975 on were transistorized, except for the CRT of course.
I have an piano organ that still has tubes. I bought a joe meek tube amplifier in 2010. Tubes add that pretty noise that sounds good when singing. I have a tube radio local broadcaster (which might be a little illegal if I push the wattage up). I wish I had your knowledge. Thanks for your service.
Tubes were used in communications amplifiers in early coaxial cable systems. Early 80s.
No. Silly me. That was awesome. I never knew how much went into this. I never knew how fm got rid of the static. Amazing how they invented this stuff. Thanx
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@@PeriscopeFilm how tiny?🤔
Nothing really amazing. It's just physics.
nobody hear invented anything it was taken from Germany at the end of ww2 or the guvment got it from the grays
Considering it was 1944 I think this is a great presentation.
Full credit to the US Army for being progressive in its teaching practice.
A good-humored and clear presenter and state of the art graphics.
Made possible by Edwin Howard Armstrong in the early 30s.
I loves these old training videos brings back memories
I'm just starting to learn Ham radio. Thank you for these films. these are awesome and helpful.
Excellent video! A nostalgic trip down memory lane back my army days at the School of Electronic Engineering in the early seventies.
Сочувствую. От вас скрывали радиопередатчики AM, FM, SSB😂😂😂
FM in the UK was referred to VHF, Very High Frequency.
VHF refers to the frequency of the AM carrier or the center frequency of the FM signal. FM modulation can occur anywhere in the RF spectrum. As a counter example, the VHF communications that aircraft use to speak to ground stations such as approach control is a VHF AM signal. As it happens, commercial FM broadcasts occur in the VHF portion of the radio spectrum, from about 50 MHz to about 300 MHz.
@@russnixon6020 During the '50s & '60s domestic radio sets in the UK would have a choice of VHF, Short Wave, Medium Wave and Long Wave as band selections until the American terms AM & FM came in.
Yous also eat beans for breakfast
@@scottkasper6378 So enlightening...
@@sapper82 You can have AM or FM in the VHF spectrum "30 MHz to 299 MHz" . VHF only means Very High frequency.
There are a couple of misconceptions in the film. First, the lightning does not alter the existing wave. It does, however, complement the signal at the receiving antenna, as any other noise, as noise has a wide band and thus gets received by the radio tuned to almost any frequency in the wide range. Secondly, while talking about benefits of FM, it's important to talk about its major drawback, that prevents it from being used at critical settings: while an AM signal being dirsupted by a noise, static or other signal could still be perceived by our ears and brain in rather harsh conditions, the FM signal in the same situation will not even get into our ears at the first place. If two FM transmitters are tuned to the same frequency or their transmission bands intersect, their frequencies will get added or subtracted due to the interference effect, with arbitrary phase shifts, and the discriminator will not even detect a signal, just a noise in the best case. That's why FM is not used often in aviation, for instance or in any other situation when two sources may be unaware of each other and may want to transmit at the same time.
To solve these problems, we use sideband... one, the bandwidth (what the officer refers to as deviation) of the signal is greatly decreased over FM and AM... two the Signal to Noise ratio is decreased... horray...! and three, with a "smaller" signal in use with Sideband we use less power... over simplified of course
@@ki4clz You must mean that the S/N is increased.
Another issue with FM is that it is line-of-sight restricted when used for two-way communication radios. FM frequencies are in the VHF band range, which is limited by line-of-sight, and that is why for overseas / international travel, aircraft are equipped with HF radios to communicate with.
Not an engineer so what you say may be true, but remember the audience for this film was military recruits with very little knowledge about FM. Excessive detail almost always confuses and frustrates the beginner detracting from the learning experience.
Heard it said once that good teachers always lie, because EVERYTHING you say can be untrue under some circumstances, and has exceptions, caveats, and edge cases which if discussed in a first lecture would hopelessly tangle the beginning student up in confusion so deep they would throw up their hands in despair. To speak clearly and simply, one must almost always oversimplify. Then once the mental 'hooks" are created on which to hand key information, you can hang additional facts or exceptions without confusing the student.
Hopefully you are not an instructor that likes to bamboozle your students so you can impress them with your brilliance or the complication of the subject. I assume you are aware of this teaching technique and were simply adding to the discussion rather than critiquing the teaching film for starting with the basics.
Hey, Sparky, it's a basic film to teach a basic concept to beginners; not to hash out every minute detail about the pros and cons of FM.
Better explained than my engineering professor. Thank you!
This is so fascinating to me I've watched it twice and plan to watch it again another day. I love the illustrations in it... Makes everything so clear to understand. I remember being a kid wondering how this worked.
This certainly "tuned"me in to be what matters in life
A tuning circuit is a whole different animal ;)
@@SoapinTrucker I know you can tune a piano but you can't tuna fish
The sound track is amazingly quiet for a 80 year old film even when there are visible scratches in the picture. There must have been some fancy processing done.
It’s so amazing we figured all this out. Imagine discovering something THAT big :O
Ohhhhhhh, that would explain why we moved most everything from AM to FM. I had always wondered why there was such a shift.
Except for aviation, in which you want to hear a weaker station if it’s in an emergency situation. Aviation is still A.M. to this day. Also, some hams use it, & C.B..
This is, by far, the best and the funniest explanation of FM I've ever seen.
Thank you!
This is the best??
@@dorol6375 The best and simpliest I've ever seen.
3:32 Somebody goofed when they put this together - the _modulator_ is where the carrier and signals are mixed together, though often the amplifier and modulator functions were done by a single tube.
Excellent videos. So much tech came from military applications we still use today.
What a manner of teaching
Thank you, Edwin Howard Armstrong! (the guy who invented FM)
This is an 80 year old video/film. Simply amazing!
Just like that Steely Dan Song "FM, no static at all"
Amazingly simple explanation! These people were geniuses!
Wow! I know this is a War Dept. film, but I am still struck with surprise when I heard swearing from a 1940s film, regardless of military men. This is a great training film, however. It's not like the information has changed over the past 80 years.
I ❤❤this channel, it's a new surprise every day.
So for the best I've watched for explaining FM. Thank you
Without computer and graphics, They made excellent and comprehensive video explaining working radio.
i started my apprenticeship as a Radio Mechanic in 1994... that course shaped my path into an AV IT Electronic Technician.
i wish we had access to material like this video as apposed to an old grumpy college teacher with a severe speech impediment.
Splendid. Keep them coming. Looking forward to some 60's technical films.
I could watch these all day.
As my ham radio Elmer told me, "The difference between AM and FM modulation is 90 degrees."
Great video....these old videos are so clear and well done.
Very informative
Це дуже важливо знати, дякую вам за працю
thank you been waiting for more fm history
This was an outstanding presentation.
Wow that's some great information.
Thanks for posting.
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Didn't not searched for it but was Worth watching it.Never thought science behind FM may be so interesting.
Incredible presentation for its time.
Finally, now I understand audio a lil better
Many thanks to Headly Lamar.
Sincere thanks for sharing!
The United States War Department delivered a science class lesson that would likely be taught in college.
My telecom and electronic training in the Air Force taught me a lot of the stuff and I still have a job almost 40 years later in the same industry. I do a lot more software than electronic nowadays though.
When times are tough, the bankers need safety so they pay for quality war videos
@@ckkmanltj Thank you for tapping or typing to me.
@@alexyo2440 I thank you for tapping or typing to me.
@@alexyo2440 Thank you for tapping or typing to me.
Ron Hinze. Call sign. KBOWAR. My late Stepfather. Was contracted to work at Area 51 back in the day. He would not talk about it at ALL!! R.I.P.
Thanks. I realy understood it now. Thanks for sharing
It's old life changing educational content like this that makes you really doubt the current quality of school/univeristy education. Time and again, I always resort to these videos for clarity.
Wonderfully explained
Great explanation.
Hey! It's our guy. Kent Smith! Peter Keating from the movie The Fountainhead. Awesome.
This channel is fantastic!
In the AM diagram, Amp and Mod boxes are switched.
After watching this fragment, I immediately went to the comments section to see how many users noticed it 🙃
Very well explained❤
I watched this film when i was goint to school at t Monmouth back in '67.
My gosh that's a well done video
I love this channel!
Went through AF electronics school in '58.
Standard text was AFM 101-8.
We also had a BUNCH of these old movies.
Wound up teaching it........then got a BSEE......taught more.....MS......then transistors, IC's, chips.......PhD in education.....ran the department..........
And retired.
Ah........history,.
I cant give a like or don't see . !!
Whatever who you are ..
What you think doing
You just give me best and special lesson more than ideas...
❤🎉
Bless bless
these are really good.
Excelente esse vídeo, é triste só velo 50 anos depois.
Thank you for preserving this and sharing it with us - people not being born at that time or lived in that place.
I'm astonished by the quality of the video, especially the animations illustrating the point. How were these animations done in 1944?
Animations were done one frame at a time and overlayed on the film
@@SavageOne420 That is a lot of work! Even more respect for creators of the video!
Whoa! The guy from the Time Tunnel! 😱
Now I understand it more clearly
Neat, thank you
Nowadays, Commercial FM radio is full of more noise than ever!!
Most of that noise is the programming, not atmospherics 😉
These days only old farts say Now-A-days 😆
Awesome video ,explanation is awesome , Do you have More video's on RF CIRCUITRY . Remote Control circuit's etc
Ha. Found a WTF moment around 2:45: when explaining the AM principle of operation, they confused the AF amplifier with the modulator.
that guy made me laugh with the static joke, and then i couldnt help thinking a dead guy made me laugh.
I don't think so - I believe that the terminology used is correct. The "modulator" modulates the plate voltage of the amplifier (at audio frequency), which produces the AM signal. The amplifier is actually unchanged (design-wise) from a fixed-gain amplifier - if you vary its input power supply voltage, you vary its output gain.
@@joshuablanton3016 No, he is correct. They confused the two. The "amplifier" amplifies the audio signal and the "modulator" modulates the radio wave.
I saw that. I think it's just a jargon issue. In a classic AM transmitter, the audio from an audio power amp is passed through a transformer whose secondary is in series with the power supply of an RF amplifier. This modulates the power supply voltage of the RF amp and this varies its output in step with the audio.
That's what I thought. The modulating signal goes into the modulator, which then 'modulates' the amp's output, according to the diagram. This means that the modulator doesn't really do much, and the amplifier has a sort of volume control, driven by the modulating signal.
Nowadays, we consider a modulator to take two signals and produce an output that is a math function of the two.
This film is obviously using the word as meaning something that takes a signal input and converts it into a form suitable for modulating.
Yes, it's clumsy, but I can see how terminology could have changed over the years.
Why are these old videos so much better at teaching and explaining than the new shit we have in schools
And 78 Years later, the FCC approves FM for CB Radio....
40kHz is some good bandwidth there! Those must have sounded great.
Thank you.
this is better than my university...
Basic electronics lessons 1972 Fort Bliss, Texas.
i love when its explained very well by a man..
amazing.
First, this is so perfectly explained, that even my dear old Grandmother could understand it.
Secondly, it's also easy to understand why hash is called hash. It hashes up the mind and personality, which is absolutely correct.
Excellent educational piece of filmstrip. Highly appreciated.
Fascinating
oh damn, they were designing dubstep sounds way back then?! wow
0:57
I miss the days when "Are you silly?" were serious fighting words
Obrigado! Thx.
The fact I’m watching this on my super computer phone doesn’t escape me
We are going away from basic science, we only see applications, this video is so wonderful because he explains basic principles here, so nice, pleasant