How FM Radio Works: A History and Exploration of Frequency Modulation

Today, we take FM radio broadcasts for granted, and some people even insist radio broadcasts are dead (hint: they’re not even close to dead). However, a gigantic amount of ingenuity went into developing frequency modulation, largely due to the efforts of one inventor and his staff. In this video, I’ll detail some of the history, the struggles, and the reasoning behind FM broadcasting. Along the way, you’ll see something you probably haven’t before: an FM radio signal in slow motion so the mechanics are clearly visible.
Major Edwin Howard Armstrong, who also developed the superheterodyne circuit that revolutionized radio receivers, spent years experimenting to make FM the force of nature it became, and always relished coming back to give it to naysayers with an epic mic drop. AM broadcasters and the corporate interests working to develop television may have gotten the upper hand on Armstrong, but he got the last laugh with stereo FM igniting a very real “golden age” for the technology, as well as FM being utilized for the audio portion of North America’s NTSC analog television standard. Armstrong never had the opportunity to see his creation’s heyday; he took his own life in 1954 as the overwhelming stress of drawn-out litigation over infringement of his FM patents crushed his mental health and drained his financial resources. Armstrong’s wife Marion, ever his supporter, continued his fight and saw every single case either decided in his estate’s favor or settled out of court.
My landing page:
BroadcastBlueprint.com
The inspiration for this video, from ‪@vwestlife‬:
• MPX Filter - What does...
Nyquist-Shannon sampling theorem:
• Nyquist-Shannon; The B...
My video on audio processors:
• How Audio Processing i...
Empire of the Air: The Men who Made Radio (PBS official site):
www.pbs.org/kenburns/empire-air/
Written and edited by Drew Kirkman
Script Editor: Dave Andrzejewski
Production Assistant: Chris Davis
Special thanks to Hive13 (www.Hive13.org/) for use of their HackRF Blue SDR
Music:
"Sunset n Beachz" performed by Ofshane
"American Idle" by RKVC
©2024 Broadcast Blueprint LLC
0:00 Introduction
0:40 Wave Properties and Modulation
1:16 Early Broadcasting and AM
2:37 Edwin Howard Armstrong vs. Carson and Others on FM
6:01 Armstrong's Wideband FM System
7:25 Armstrong Drops the Mic
8:49 Quirks of FM
11:04 W2XMN, the First FM Station
12:03 The Guitar String Analogy
12:54 FM Demo Setup
14:01 An Unmodulated FM Carrier
15:03 FM in Slow Motion - Modulated at 1 Hz
16:06 Tracing Music on the Waterfall
16:27 Modulation Index and Audio Processors
18:29 Multiplex (MPX) Operation
20:35 MPX Demonstration and the Pilot Tone
21:14 Stereophonic Sound and Vinyl Records
24:12 FM Stereo Overview
24:56 AM Components of FM Signals
29:10 The Algebra Behind FM Stereo
30:40 Using Carson's Math to Improve FM
31:26 Pre-emphasis and De-emphasis
32:28 Empire of the Air: The Men who Made Radio
33:17 Conclusion

[@WECB640]

This is beautifully presented. It is easy for the layman to understand, yet enjoyable for the radio engineer at the same time. Take a bow, you earned it. 73

[@BroadcastBlueprint]

Thank you so much!

[@gordonsmith8440]

I’ve been trying to get over the broad-strokes understanding of FM stereo radio hump for like 5 years and this video finally did it. I was just looking for something to watch while I made coffee. You’re making the internet a better place, thanks!

[@BroadcastBlueprint]

I’m glad it helped! Thank you for watching

[@redthepost]

Thank you for helping me resurrect my interest in broadcasting technology. Fun stuff.

[@hugh007]

The best description of AM and FM I've seen. 100 years of radio in 34 minutes: quite a feat. I had the privilege of meeting Tom Lewis when his book was released and the film was in production. Thanks for all your work. K4XBC

[@BroadcastBlueprint]

That’s high praise! Thank you so much!

[@turbo2ltr]

two thumbs up. great video.

[@jaredbater6229]

What an absolutely fantastic video. Amazing explanations!

[@BroadcastBlueprint]

Glad you liked it!

[@michaelcox436]

Excellent, thank you

[@ChrisGoosman]

Fantastic video! Pre- and De- emphasis, as well as the curves used in various noise reductions schemes, is also somewhat analogous to the RIAA curve used when cutting and then playing back vinyl. I've been involved in disc cutting in my lifetime, and like FM, it's magic and a wonder that it works as well as it does, ha!

[@BroadcastBlueprint]

When I want the challenge of not knowing why something works when it clearly shouldn’t, I go straight to audio and RF electronics!

[@cateclism316]

I understand AM and FM a little better because I worked with analog music synthesizers in college. I also remember FM's ascendance in the 1970s, and how crisp and clear it was compared to AM stations.

[@xtlmeth]

Thank you for naming this video and taking the time to put so much detail.

[@TVJAY]

This is an amazing video. Thank you for making it. I will share this with a lot of people.

[@AA5SA]

An amazingly good video!

[@sophiapriest]

I love this video! It was so informational, and I loved the metaphors and examples you provided as well. I'm slowly learning about this type of stuff to someday work in the radio industry, and I this also explained a lot about things I've noticed but didn't understand much about while using my SDR! Thanks for this video, and I can't wait to see what you'll upload next!

[@BroadcastBlueprint]

Glad it helped you learn something new! That's my goal when making these videos.

[@christopherjones2283]

bravo! well done professor

[@barrygeary1890]

Has pre emphasis on fm anything to do with reducing high frequencys?

[@BroadcastBlueprint]

Sort of… since there’s more noise at higher audio frequencies in the demodulated signal, pre-emphasis helps reduce that high frequency noise while trying to keep the modulating signal intact.

[@StringerNews1]

We should remember that radio broadcasting didn't commence until ~1920 because amplitude modulation needed the enabling technology of the triode tube, for amplification and mixing. Also, while Lee De Forest's name is on the patent, he didn't invent it really. De Forest was the first at the patent office, but his understanding of how it worked was non-existent. It took the work of others to discover uses for the triode tube that De Forest simply couldn't conceive himself. Today we'd call De Forest a patent troll. I remember learning the mathematical relationships between the baseband audio signal and the modulated AM and FM signals, and marveling that someone had the insight to figure that out. The people who actually did suss out the math deserve the credit far more than De Forest.

[@BroadcastBlueprint]

That's a really important point - Lee de Forest didn't really understand the triode and it wasn't until other people like Armstrong started picking it apart that it found real usefulness. Of course, his personality would not stand for such a thing, so he took all these people to court and spent the rest of his life trying to convince everyone that he deserved all the credit. His autobiography is called "The Father of Radio" for crying out loud. The segments of the "This Is Your Life" television program with Lee de Forest featured in the Ken Burns documentary were nothing less than cringeworthy. The letter de Forest wrote to Carl Dreher after Dreher *dared* to pay tribute to Armstrong in Harper's Magazine after his death was dripping with pettiness. History has thankfully not shown Lee de Forest in the most favorable light, and it really is a shame that Armstrong didn't live to see his full vindication and how popular his creation ended up becoming.

[@StringerNews1]

@@BroadcastBlueprint yes, also noteworthy is that De Forest was a contemporary of Nikola Tesla, a person who has been deified of late by the woo-woo pseudoscience crowd. As with De Forest, Tesla's self-cultivated image doesn't really jibe with his actual body of work, that peaked with two patents for AC induction motors that look nearly identical to what Galileo Ferraris published in Turin, Italy just a year before Tesla got onto a boat to the US, and headed straight to the patent office. After that, Tesla's alleged genius never produced any working science or technology. I think that in both cases, the personality cults were created to wishcast a reality that they wanted for themselves, but which they didn't actually achieve. That's why I admire great ideas more so than great men.

[@jamesmatheson4746]

Explain HD AM and FM. Most broadcasters have given up on HD AM