Armstrong: the Tragic History and Physics of FM Radio

How Howard Armstrong created and detected frequency modulation (FM) radio and how it was so impressive that it actually caused his downfall!

Some links:
Very good video but, unfortunately, the methods that they described were not used by Armstrong. Still A+

OK video, not as detailed as the 1944 one.

The background music was from Kim Nalley and the "New Orleans Hop Scop Blues" which is by Jimmy Noone.

The theme song is by Kim Nalley and is a cover of "Electricity Electricity" from Schoolhouse Rock :)

[kirkp_nextguitar]

I got interested in electronics and electromagnetic waves by discovering my grandad’s 1922-23 radio textbooks and some old radios in the attic, and ended up in a related career. The history was part of the fascination. You’ve done a great job of presenting it.

[ntcrwler]

A simple and easy to understand explanation. Thank you! Edwin Howard Armstrong has always been one of my favorite inventors and inspirations. And what Sarnoff did to him was unforgivable!

[JuanPab]

Armstrong invented the receiver regenenative, heterodyne and the superheterodyne. He is the great radio inventor. Chapeau

[aramboodakian]

This is truly a story with a tragic ending (very sadly) and not click bate like so many other YouTube posts. Thank you for the history.

[etmax]

Well that was way more interesting than I thought it would be. Thank you very much. Interesting how complex the original discriminator was compared to the 60's when I got into the game. It also demonstrated what was (is) so seriously wrong with the US patent system. Sarnoff shouldn't have only been fined, he should have been jailed along with all of his lying engineers and anyone else that colluded.

[timothystockman]

In order to get enough frequency deviation, Armstrong not only multiplied a low frequency signal many times, he took the resulting high frequency signal and heterodyned it back down so he could multiply it many more times, then he once again heterodyned it back down and multipiled it more. All of this multiplication finally gave him enough deviation.

When I started high school around 1970, our school started an FM radio station WCNE, which is now community station WOBO. Our first transmitter was a CCA FM10D, which used a low frequency crystal oscillator driving phase modulator. Phase shift and frequency shift are essentially similar types of modulation. In order to get enough deviation for broadcast, the FM10D had several multiplier stages, similar to Armstrong's Columbia prototype.

In fact, the de-emphasis network in the FM receiver, integrates the audio waveform above the knee of the de-emphasis curve with 6 dB per octave, essentially making high frequency audio compatible with a phase modulator. A phase modulated FM transmitter has what is called a pre-distortion network to adjust low frequency audio to be compatible with the de-emphasis curve. Note that the purpose of emphasis is to reduce high frequency noise, which is caused by the equal energy-per-octave response of the ear. It is just that de-emphasis can do double duty, both reducing the HF noise and integrating phase modulation. It seems this subtlety is missed by the amateur radio examination which wrongly asserts that the PURPOSE of de-emphasis is make an FM receiver compatible with a phase modulator; this is a byproduct, not the purpose.

It is somewhat complex to generate a stereo signal using frequency multipliers, so as stereo took hold in the late 1960s, Gates developed the TE-3 direct FM stereo exciter. The problem was that a crystal oscillator could not be "pulled" far enough for wideband modulation, so the TE-3 had a complicated phase-locked-loop automatic frequency control system to loosely lock the FM oscillator to a crystal reference. The problem was that certain audio, particularly heavy bass, would cause the AFC to unlock and the station would drift. Disco music of the mid and late 1970s was the death of the TE-3. As the 1980s were getting started, Harris (who had bought Gates) came up with the MS-15 exciter, which was a direct FM unit with a much improved AFC system. My experience with the TE-3 was at WMRI and the MS-15 was at WKHY.

So far as AM, broadcast could and did have good fidelity. When I worked at WBAA, our 5 kW Collins 21A transmitter had audio frequency response only 2 dB down at 15 kHz, which I measured. I had 2 different EE professors at Purdue tell me that AM broadcast stations must limit their audio to 5 kHz, which is completely incorrect. But a lot of people apparently believe this myth. In the early 1980s, the FCC started requiring stations to limit audio to 10 kHz (the NRSC emissions mask) so they could overpopulate the broadcast band. Wideband (10 kHz) c-quam stereo AM can sound amazingly good, but as time goes on modern electrical devices are raising the noise floor so that AM reception in cities may be too noisy. A couple years ago, during an extended power outage, I did some amazing AM broadcast DXing!

I have found it sad that few people working in broadcast know the names Fessenden and Armstrong, radio pioneers who created their industry.

[Dave]

Your series of videos is really great. Please keep up the good work! Your subject may not appeal to everyone (I wish it did), but I am sure there is a small subset of viewers that really appreciate the work you have put into these videos!

[erikziak]

Great series. YouTube should finally boost these videos, they are very valuable, as they tie together good explanation of how things work based on our knowledge of natural laws, the people who discovered them, and economy and politics together in a complete image. Everybody can learn something new from these videos. Truly great work. Hope your channel goes viral, it deserves it. The quality, precision and a good narrative communicated pleasantly and simply (yet not oversimplyfied) of your videos beats all those clickbait hype "tech", quantity content on YouTube. Other videos will be forgotten by history, but these are timeless.

[MachRadioIntercepts]

Great work, Kathy! Thanks for bringing us this great history of FM radio. Back when I was a flight instructor near NYC, we used the "Alpine Tower" as a visual landmark for flying up and down the Hudson. I never knew that tower's connection to FM broadcasting.

Armstrong did so much for us who depend on radio.

[rollomaughfling]

Ok, this is an instant sub. I'm a little upset Youtube's been sleeping on this channel in my reccs. Fantastic job, Kathy!

[gregoryignatius]

Your channel is great. I love the straightforward and clear explanations of some very difficult material. You will probably never make as much as perhaps you should but from some of us who have lived through a lot of this, you have a great channel.

[vartannazarian]

Thank you so much for such an informative video Kathy. You were able to include so much important information in just 12 min. For me, Armstrong is the greatest American engineer.

[srvr]

This is my new favorite channel. Thank you so much for making these videos.

[dell]

Thank you for that great explanation. I still have the 1950's FM radio Tech Manual I filched from the army when I was working in communications in Korea. Your explanation makes a lot more sense than theirs did to someone new to the field.

[sundog]

You are a great presenter. Although I already know the technological details you present, the history you present and your enthusiasm make it a delight to watch.

[AnbroBR]

Very good video, Kathy! Major Armstrong truly WAS the "father" of radio, NOT de Forest. Armstrong took de Forest's Audion and actually figured out how it worked and why, de Forest really not having a clue as to its operation. Armstrong then developed circuitry which would amplify radio signals and also generate them. He went on and invented the regenerative, super-regenerative and superheterodyne circuitry, circuits which we still use today in all AM & FM radios, in television and in cell phones. Armstrong also, as this video explains, invented wide-band FM radio, which was truly "high fidelity" and also FM multiplexing. All this is explained in PBS' documentary "Empire of the Air: The Men Who Made Radio."

As an amateur radio (ham radio) operator, for the past three years, I have put on a special event, using my ham radio station at my home, in honor of Major Armstrong. I have a special FCC call sign assigned to me and I try to make it a 3-day affair. I use Morse Code only and try to work as many other hams here in the USA and around the world as possible. This is my on-going effort to honor Major Edwin Howard Armstrong. Truly a great man! Thank you.

[mrsagain]

Thank you, Kathy, for the indeed clear description of Armstrong’s FM. Had been looking for this and per your comment, couldn’t find anything but the tragic storyline. I sincerely admire your ability to produce these wonderful videos!

[notvalidcharacters]

THANKS for this, Armstrong is a hero of mine and it's always satisfying to see his story told as it deserves..

[kbdrh]

Howard Armstrong was a genius! His demise was tragic. Rest in peace Howard. Kathy nice

[j.vonhogen]

Wow, what a sad story! I wasn't expecting such tragic ending.
Thank you for your great videos!