The 50 year old headphone dongle

If you think headphone dongles are just a new irritation - think again. But at least Sanyo's Stereocast added something new to the portable listening experience.
00:00 Introduction
03:31 Compatible devices
04:35 What’s inside
05:35 Why?
07:22 Demo
08:23 FM Mono vs Stereo
12:15 Do all new FM radios do stereo?
15:50 What goes around...
16:59 Patron credits
MERCHANDISE
New Techmoan Merchandise is now available.
etsy.me/3zzjweo
SUBSCRIBE
kzbin.info?...
SUPPORT
This channel can be supported through Patreon
/ techmoan
******Patrons usually have early access to videos******
OUTRO MUSIC
Over Time - Vibe Tracks • Over Time - Vibe Track...
OUTRO SOUND EFFECT
ThatSFXGuy - • Six Million Dollar man...
AFFILIATED LINKS/ADVERTISING NOTICE
All links are Affiliated where possible.
When you click on links to various merchants posted here and make a purchase, this can result in me earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network & Amazon.
I am a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to AMAZON Sites (including, but not limited to Amazon US/UK/DE/ES/FR/NL/IT/CAN)
Regularly asked question
Q) Why are there comments from days ago when this video has just gone live today?
A) Patrons / techmoan usually have early access to videos. I'll show the first version of a video on Patreon and often the feedback I get results in a video going through further revisions to improve it. e.g. Fix audio issues, clarify points, add extra footage or cut extraneous things out. The video that goes live on youtube is the final version. If you want to see the videos early and before any adverts are added, you can sign up to Patreon here: / techmoan

[@vk3crg]

I work in radio broadcasting. FM transmitters are inherently mono devices. The stereo encoding is often done by a separate device that’s not even part of the transmitter, sometimes the audio processor before the transmitter, sometimes the RF exciter or sometimes even the RDS encoder. In stereo FM broadcasting there is a 19Khz pilot tone which tells the radio it’s a stereo signal. This is what lights the FM stereo light and is why audio broadcast on FM had a strict and sharp audio filter which cuts any audio frequencies above 15Khz otherwise the audio high frequencies (up to 20Khz) can interfere with the 19Khz pilot tone (which you can’t hear but it’s there!) I wonder what it sounds like to dogs near FM radios! 😂if the pilot tone level is set too high at the transmitter some (young!) people on some radios can actually hear it! Also if the audio frequencies are not cut above 15Khz this causes the radio to drop in and out of stereo due to the audio frequencies encroaching onto the 19 Khz pilot tone. The audio input into most FM transmitters is actually a single multiplexed audio signal (not a separate left and right) so in effect the FM transmitter is actually mono but is blindly transmitting an encoded audio signal including 19 KHz pilot tone. Great little device in this video! Keep up the great work! Craig - Australia

[@diracflux]

Fantastic explanation. Thanks Craig.

[@RJDA.Dakota]

When I was much younger when we had the CRT screens , the above 15 kHz tone from the screen itself would drive me crazy.

[@worldcomicsreview354]

Not entirely related, but ages ago I read a story from a collector of acoustic gramophones. He said a toddler he knew really liked one, but would cry when another was played. Maybe there was some sort of harsh screech coming from it that adults couldn't hear

[@cooldudicus7668]

Is it possible to hear the 19 KHz tone if the radio is about out of range of the transmitter? I had heard a carrier tone on FM radio when driving in the past. It happens around the time when I start getting out of range of a radio station.

[@StackOverflow80]

It's right, but I guess these days in pro area all the stereo mux is generated digitally and fed into FM modulator of the transmitter, or even entire high frequency FM signal can be generated digitally, amplified and fed directly into antenna. Pilot signal, besides making stereo light on, has another important role, and it is to enable to recreate suppresed 38kHz subcarrier (it is suppressed to save modulation power, also pilot signal is quite weak for the same reason). Pilot signal is exact half frequency of the subcarrier and it is in phase with it. Because early stereo decoders used simple diode demodulators, the subcarrier and both sidebands present was mandatory. Nowadays of course only one side band with no subcarrier would be sufficient, but back then, to be able to keep stereo decoders simple, such arrangement was necessary.

[@guni82]

Here in Austria back in the 90s radio stations used to turn off the stereo carrier during traffic announcements so you could understand it better when having bad reception.

[@Knaeckebrotsaege]

My Blaupunkt car radios from the 90s to mid 00s always force the traffic announcements (the ones that cut into whatever tape/cd/mp3 you were listening to) to be in mono. You can actually force this if you have one of those little FM transmitters and send out a "hinz triller" over it. The radio will respond by pausing tape/cd/mp3 playback, increasing the volume and switching to mono for as long as the traffic announcement lasts

[@unclehogram]

@@Knaeckebrotsaege I remember Blaupunkt releasing radios that worked this way in Germany, think it was called ARI? Would switch to another station for traffic messages. Turned it off because keine deutsche sprechen but it WAS cool.

[@PascalGienger]

​@@unclehogramARI was the proprietary system to indicate a traffic information is broadcast. This feature has been included in RDS nowadays in Europe.

[@Rich_123]

This is instantly one of my top Techmoan videos. What started as an obscure piece of AV history led us through a tunnel of how FM stereo came to be what it is today. Some great bonus tidbits in the comments too!

[@EzeeLinux]

FM stereo radios in cars often have what is known as a "blend circuit." It reduces stereo separation and cuts noise as the signal gets weaker.

[@InfiniteColorsMusic]

I was about to write exactly this. A tuner chip I worked with goes as far as giving the possibility to configure the response slope of the stereo blending circuit. On such tuners, the "stereo" indicator (if at all implemented) usually comes on if there is at least some stereo signal in the mix (that is, if the reception hasn't been switched to full mono)

[@XMguy]

They try that Blend with HD Radio in the states as well. Annoying.

[@derek20la]

@@XMguy You're confusing two different things. What Joe meant was as an FM signal gets weaker and noise level increases, radios in modern cars will "switch off" stereo in decreasing steps until it is completely in mono. What you described is when a station broadcasting in HD Radio fails to keep their analog and digital signals in sync (which happens far too often). If the digital signal fades, the radio is supposed to seamlessly switch back to analog FM, but when the sync drifts, switching causes a 1 or 2 second audio skip. Only the station can correct it.

[@EzeeLinux]

@@XMguy HD only works IF you have a strong signal anyway. The US iBiquity system is garbage. :(

[@XMguy]

@@EzeeLinux It should not be a license based system.

[@Allan_aka_RocKITEman]

TECHMOAN: _"It's deja vu all over again."_ To which I would add: _"The future DEFINITELY ISN'T what it used to be."_

[@JWD1992]

I admit I had no idea that FM actually went out in mono and then got converted into stereo. But now I do remember over the years how the stereo indicator light would not light up if the station wasn't tuned in all the way, which I now know means that the 53kHz signal which allows for the conversion wasn't coming in. Fascinating.

[@DanielMReck]

7:34 Loving the intense gravitas of the Greatest Hits Radio ident. Not sure whether we're about to hear some fabulous tunes or just some profoundly important breaking news.

[@jmulvey371]

My old college radio station in New Jersey was FM mono. That was simply the result of the college having been granted an early FM broadcast license (educational institutions were among the first licensees) and a pile of Cold War-era military broadcasting equipment, but no real budget. Our volunteer engineers worked miracles patching it together and we took full advantage by saturating a 3-mile radius with R.E.M., Meat Puppets and Robyn Hitchcock all day long.

[@SenileOtaku]

WFDU perhaps?

[@jmulvey371]

@@SenileOtaku Ha! No, although my sister went there. This was at Middlesex County College --though we usually referred to it as "The University of Edison."

[@endymallorn]

@@SenileOtaku@J Mulvey Or WMSC?

[@scottlarson1548]

One fun thing about the mono college station in my area (shut down a few years ago) is that they had no 15 kHz filter since there was no stereo signal to protect. That meant that sometimes cymbal crashes would fool stereo receivers into briefly turning the stereo light on since they sounded like a 19 kHz pilot tone.

[@fsphil]

If you capture that stereo output at a high enough sample rate, you may be able to see the 19khz pilot tone and the stereo difference signal at 38kHz in Audacity. It might even show the extra noise that lives up at 38kHz causing the stereo-only noise.

[@SeanBZA]

Going to also need to sample at a much higher rate than the more common 44kHz, as those tend to start rolling off from 12kHz, and have a pretty steep attenuation at 19kHz, specifically to avoid birdies from beating with that pilot residue. You would need to sample at 96kHz or higher, to get enough bandwidth to accurately reconstruct the full stereo signal digitally, and would also need to get an output direct from the FM detector as well, as most of the audio chain would have low pass filtering that strips this. Pretty much excludes all common ADC units, you would need one that is designed for high sample rate and high bandwidth, definitely not an audio one.

[@fsphil]

@@SeanBZA Yes, I should clarify I meant capture the special stereo output socket that is used for the dongle - it should be providing the entire baseband signal, stereo sub-carriers and all.

[@y0uRF4t3]

@@SeanBZA High quality professional audio interfaces sample a 192kHz, 32bit, for example my Steinberg UR22C.

[@SeanBZA]

@@y0uRF4t3 Yes, but a lot of them do low pass filtering to remove the ultrasonic signals out. 192kHz sampling just means that you can use low order filters, and not have too much phase noise in the signal, unlike the terrible high order Bessel filters you need with 44khz sampling, which gives some truly odd phase shifts in the audio passband, as a consequence of needing to get at least 30dB of attenuation at 22kHz so as to prevent aliasing. Higher sampling rate then a digital downconversion makes the analogue filtering much simpler, and more linear.

[@PaulsOldVids]

Not all radios filtered out the pilot tone and this could interfere with the bias and noise reduction circuitry of cassette decks. Consequently, many were built with a 19Khz notch filter to remove the pilot tone when recording

[@FranLab]

Yea, all FM stations are broadcast in mono which is done by design as the requirement in the 60's for all "new" stereo equipment be retroactively comparable with pre-stereo systems from the 50's, so they use a left-minus-right system where the right channel information is multiplexed on the main carrier signal in a secondary carrier which the stereo system detects, and subtracting that embedded audio signal from the mono reveals the left channel. Early stereo receivers typically had a control to allow you to determine how much separation you'd get, or allow you to listen in mono at much higher fidelity.

[@skylined5534]

I remember the stereo/mono switches on 80s to early 90s car stereos very well! Them woz the days !

[@marcusdamberger]

@@skylined5534 Yup, while on the freeway I remember you could eke out a little more range and listenability on a weaker station as you were driving away from it. Or if you were closer to the fringe or in a city with lots of tall buildings and got that annoying stereo picket fencing you hit the stereo/mono switch.

[@kaitlyn__L]

Fran watches Techmoan? What a shock! :p

[@josephaltman460]

They should have advertised it as "Stereo Ready" with dongle. Like we did for satellite and HD radio in the 2010s.

[@tomkurcz6669]

You gave the meanin of Yogi Berra's '"It's like Deja Vu all over again"' a new meaning!!!

[@markjamesmeli2520]

For decades I've wondered why hitting the mono switch on an old FM radio cleaned up the received signal. Now I know. I also know that there seemingly seems to be many FM radio stations broadcasting in mono. Your animated flag at 11:57 explains why I've always noticed that on the car radio, since that's mostly the only time I listen to radio anymore. As for back in the day, I guess Sanyo really needed that extra 12 bucks.

[@uxwbill]

It's worth noting that your car radio is very likely to have a fairly aggressive stereo blending circuit. The goal is to try and strike a balance between having some degree of stereo separation while suppressing interference and noise.

[@Zarkovision]

In the 1960s, when stereo FM came up, also the European brands like Grundig sold big box radios with valves and a "Stereo" logo, but the stereo demodulator was optional, and also made 50% of the price of the radio. But when you've paid 560 DM for example your Grundig 5295 here in Germany you really thought twice about spending another 250 DM for the stereo demodulator... Most people didn't until transistors made stereo FM much cheaper and a normal thing at least at the big box radios.

[@professormicron6470]

5295 wasn't even compatible with Grundig stereo adapters because they haven't come out yet. Grundig was late to FM stereo party by around 1-2 years. Their first decoder for European market came out in 1963. Maybe they were more careful with market strategy than other brands and decided to wait. I have a 5299 which is exactly the same as 5295 but without speakers and it would be the only European tube receiver you need in your life if not for lack of FM stereo... It even has a phono preamp (not every example but some were outfitted with one). And then you've got radios from Saba and Philips that have FM stereo but guess what they didn't offer? Yeah the didn't offer phono preamps for their radios. I've actually spent some time researching if there ever was a mid-century styled (so 1962/1963 at newest- almost everything after that is just ugly) European (would be German anyway) tube device with FM stereo and phono input and I'm 99% sure that there wasn't even a single model like that:(. The earliest German devices with that kind of features are already in the modern minimalist style and usually hybrid designs with tube tuner and transistor amp. Grundigs also got quite ugly just as they introduced stereo decoders. There were some slightly earlier, less ugly stereo compatible tube radios from other brands that I have personal experience with and it that aligns exactly with what you say- the decoders for them mostly exist on paper. Interestingly Grundig decoders actually appear for sale from time to time, so maybe introducing them a year later helped sales. First tube radio I stumbled across that can equip a stereo decoder is a Körting Berlin (not a bad design despite zero brand recognition) and I've seen the original stereo decoder for it once but I wasn't able to buy it. I decided to get a first one that comes up but it's been 4 years of waiting so far. That's how rare these things are, at least anywhere in Europe. I found that the golden rule of 1960s high end tech also applies here- no matter where it was made, you'll still only find it in the US. Few years ago I accidentally stumbled across a Loewe Opta from 1962 that was made especially for US market and it came with FM stereo decoders as standard- almost the same exact decoder that nobody bought in Germany. And the most interesting thing is that it isn't even a high end tube radio, just an entry-level stereo model that someone decided to sell with stereo decoders as standard. It doesn't even have a stereo pilot indicator, only a magic eye. It's the most ironic thing ever, living just around the corner from Germany but if you want a German tube radio with FM stereo you'll have to transport it through half of the world. Alternatively you have to wait like 3-5 years for a chance that someone locally will sell you a good Japanese tube receiver that has everything built in. It's not a good life if you really want a tube stereo, especially on this continent

[@SenileOtaku]

Yes, that was the case with our Telefunken Concertino 5384. It has the place on the back to plug in the stereo module, but we never had one. Still have it, which Dad bought new in the early 1960's, but having seen the videos on radio restoration on Mr Carlson's Lab, I'm hesitant to plug it in after i t sat unused for 20+ years (probably more like 30).

[@AaronSmart.online]

I have a Bang & Olufsen Beomaster 900, a transistor receiver from the mid-late '60s, and the stereo demodulator was optional although installed in my example. If the demodulator is not installed, the "stereo" lamp is still illuminated if you select the tape or phono inputs and have the mono switch off.

[@Devo_gx]

Also, you should grab a little SDR receiver and hook it up to a computer, as you'll actually be able to see a visualization of how the tuner is detecting the FM stereo information. Using an SDR is so much fun as you get to actually see the radio spectrum

[@BingoLarsson]

Indeed! Also the difference between AM/FM modulation makes lot more sense when looking at the waterfall. Might also be a helpful tool to figure the RFI issue he has mentioned in quite a lot of videos.

[@wrenchmonkey3920]

top tip. mite even spur viewers to get their amature radio ticket.

[@namesurname4666]

@@jiriwichern i have an rtl sdr v3 and reception is worse than any radio i have (with the same antenna) but it's still interesting and fun to use

[@fflynnful]

You can also see the HD (hybrid digital, not high definition) subcarriers on HD stations. There is HD decoder software for PC.

[@Devo_gx]

@@fflynnful indeed. Techmoan won't see that as HD Radio isn't available there, but there is DAB decoder software too.

[@JaredConnell]

Today someone posted on LGRs video that every week techmoan and LGR are getting closer and closer to their childhood. And I thought to myself, have you seen techmoans videos lately? Shellac records and NSYNC cellphone toys don't seem like contemporaries to me lol. And this video proves my point even more, but that's why i like this and LGRs channel, you never really know what you're going to get!

[@jooei2810]

Techmoan, the corner stone of KZbin!

[@markmarkofkane8167]

The most interesting person on KZbin!

[@pedrodaniellopesferreira2916]

@@markmarkofkane8167 in never miss one of his videos.

[@eugeniughego2124]

this guy wakes up in the morning and asks himself: "what tech from decades ago can I make interesting and entertaining?"

[@robertschnobert9090]

​@@markmarkofkane8167 I love Mr Moan 🌈

[@frstwhsprs]

@@markmarkofkane8167 All tech, no moan!

[@helge.]

As someone who worked for Apple in the past your last comment on the adapters made me smirk a lot! Thanks for that!

[@organfairy]

In the 1960s it was quite common to sell 'stereo' radios without stereo - that is: They could amplify stereo sound from a stereo taperecorder or stereo grammophone, but they couldn't decode stereo radio. The reason was that many countries didn't broadcast stereo yet, and since it would make the radio more expensive to include a stereo decoder, they left it out but you could have it added later as there was a socket somewhere inside or in the back for the decoder module. In Denmark Program 1 - that played mostly classical music - got stereo in 1966, where Program 3 - that played pop music mostly for the casual listener - got stereo as late as 1972.

[@MrDuncl]

I went down the rabbit hole of looking at the decoder modules for tube/valve radios. One article suggested they needed more critical factory adjustments than the radios themselves.

[@mark314158]

Strangely in the UK Radio 1 played pop while Radio 3 was classical...

[@UHF43]

And those that had the integrated stereo demodulator were marketed as Full Stereo (or Voll Stereo in German)

[@organfairy]

@@mark314158 In Denmark the reason for our numbering was that DR - Radio Denmark (state owned and works much like BBC) didn't consider pop and rock to be worthy of broadcasting to the listeners. The controllers of DR came with a classical background and therefore wanted no such thing as music which only had the qualification that it was 'popular at the moment' (I imagine these controllers as people like Sir Humphrey from 'Yes, Minister') . DR had two programs, 1 and 2. But then came 'Radio Mercur' which was almost 1:1 like Radio Caroline in the UK. They transmitted from a boat outside Danish territory and they were really popular and often had more listeners than DR. In 1962 the Danish government made a controversial law that made it illegal for Danish people to appear in radio programmes not made for DR which effectively made it impossible for Radio Mercur to survive. But then program 3 was launched and it was meant as replacement for Radio Mercur - in fact many of the people who had worked for Mercur was now working for Program 3.

[@MrDuncl]

@@mark314158 Radio 3 was previously the Third programme which was also Classical. It was the only one of the four main stations where there was any continuity in the name. The Home Service (news and talk) became Radio 4, while the Light Programme (which played the likes of The Andrews Sisters) became Radio 2. Nowadays, Radio 2 is the most popular station, playing the likes of Madonna who was deemed to now be far too old for Radio 1.

[@ReluctantDruid]

Good to know that even after 40 odd years of listening to radio through headphones, that we can still be taught something. Thank you for your continuous teaching and entertaining. 😊

[@bobblum5973]

The same basic technique used to encode stereo sound into FM broadcasts was used to add stereo audio to NTSC television broadcast audio. A combined L+R monaural signal is mixed with a L-R (inverted R) signal subcarrier, canceling out the R to decode a 2L left channel signal, and likewise L+R mixed with an R-L (inverted L-R) to get a 2R right channel audio signal. [ _Much_ easier to diagram it than describing it in a short comment! 🙂 ]

[@derek20la]

The FM band begins where NTSC channel 6 ends. Technically, the audio subcarrier of an analog broadcast on channel 6 is at 87.75 MHz. Even with the small frequency offset, it was "close enough" for most radios to easily tune. My memory of analog TV was listening to XETV channel 6 from Tijuana at 87.7 FM... and I lived in the San Fernando Valley of LA, 150 miles away to the north, due to tropospheric ducting most of the year.

[@fflynnful]

And the L-R was run through a dbx compander for noise reduction and the pilot tone was 15,750, the horizontal sweep rate for NTSC.

[@nfalister2732]

And the pilot tone was at 15.734kHz, so an FM stereo demodulator wouldn't lock on to it unless you modified it for the purpose. My parents had an early RCA "monitor" grade TV that had a multiplex output and line inputs (with stereo speakers even) but NO stereo demodulator. I found a schematic for a TV stereo demodulator in a magazine and retrofitted the RCA to have stereo audio back in 1982 or so. We had one "stereo" station in our market at that time. I thought we were so high tech!

[@ntsecrets]

@@fflynnful which is why the encoders needed the video signal as well so it can use the horiz rate for encoding!

[@bobblum5973]

For those questioning the 15750 KHz vs. 15734 KHz in the other comments, simply stated the 15750 was matched with 60 Hz for black and white, but tweaked to 15734 & 59.94 Hz for color to avoid artifacts in the picture. Similarly, the colorburst frequency isn't 3.58 MHz, it's 3.579545. Probably more than you wanted to know... 🙂

[@Adventurepil0t]

I would love a video on AM STEREO. Back in 1992 (in Australia) my dad had a mid tier Toyota celica (SX) and it had a button for AM stereo and it worked surprisingly well. The funny thing is I’ve never seen that option on any radio, car or not before or since. I wondered if it just split some random frequencies and just throw them on different sides, I don’t know. Have you ever seen such a system?

[@VintageTechFan]

Most systems use quadrature amplitude modulation. How that works is hard to explain in a few simple words, but basically it is a normal AM radio signal modulated with the L+R sum signal to archive compatibility with mono receivers. Then they add a difference signal L-R modulated onto a supressed, but 90° phase shifted carrier, which cancels itself out in a classic AM demodulator, but can be detected by specialized circuitry and used to reconstruct the L and R channels. It just needs the bandwidth of a classic AM station. The transmitter side is much more complicated since you can't use high level modulation, but have to create the signal on low level and linearly amplify it, which is less efficient.

[@dan_from_australia]

No, it is genuine stereo, and yes it is fascinating technically. Australia used the Motorola CQuam system based on a quadrature modulation as mentioned by Nitro. Unfortunately only one or two stations in Aus still use this system.

[@Adventurepil0t]

@@dan_from_australia ah, that would explain why some of the AM radio promo stickers like 2WS had stereo written on them!

[@AaronSmart.online]

VWestlife and Shango066 have done some videos on AM stereo. It was never really a thing in Europe so it's unlikely Mat will cover it

[@Audiorevue]

I had a old receiver I can't remember the brand but it had an option for AM stereo, matter of fact that's why I bought it. Obviously I wouldn't be receiving am stereo but I just thought it was sort of a rare tech and kind of neat

[@sgtsquank]

You nailed the reason why we still use our receivers 'mono' option. We live in a valley with terrible signal reception -- stereo will come in, but not very well. Mono generally will come in clear and with things like NPR, mono works fine.

[@Bonedadyo]

When I was a kid (in the early 1970’s) we had an amp/receiver that had the FM stereo/mono switch. The stereo signal was so bad it was basically unlistenable. My father put a piece of tape over the switch to make sure it stayed on mono! Haha!

[@Velodynamic]

In the 1980's when I was a kid we had a Grundig "boombox" stereo cassette player with tuner that had a dedicated slide just under the cassette player that went from "stereo" to "super stereo". Nobody really heard much difference but it stayed on "super stereo". lol

[@adamrichards3174]

We have what are known as LP stations here in the States. As in Low Power fm. One in particular, WWSA-LP is a non-profit volunteer ran oldies station that I've been involved with since 2016. From day 1, it has broadcast in FM mono. Every bit of audio runs through a circa 1969-70 RCA mono broadcast console, with the lovely rotary faders.

[@revidual]

My dad bought a big square chocolate brown mono radio in the late 70's, it came with brown headphones connected with a multipin plug. Its two channel output allowing me to enjoy The Hitchhikers Guide to the Galaxy in glorious stereo.

[@tortysoft]

I had a cassette radio that I bought in 1976, I recorded HitchHicker in stereo on it back then. That radio wakes us every morning to this day :-) I'm reading the full 'HHGttG books on my podcast 'tortytalks' by the way !

[@marcusdamberger]

I think the key takeaway here is BROWN! (it was the 70's after all)

[@paulstubbs7678]

Brings back memories, Many years ago, Tandy electronics often sold oddball IC's, on one occasion it was a FM stereo demodulator IC, so I basically built one of these - well almost, as mine only output line level audio. In the early days of FM, you could buy an FM adapter for your AM car radio, these were a simple FM radio that fed an AM modulator, so you could listen via your car's AM radio. I had scored one of these and I had tapped into the audio before it hit the internal AM modulator, this I fed into the above mentioned decoder, and it worked first thing - way more success than what you just had with the Sony AM radio. Maybe my savveier was the fact that adapter was quite small, so they had skipped anything they could, like filters on the output to remove the FM stereo pilot tone, something the target AM radio could not reproduce anyway, so why bother filtering it out. On another oddball point, I am listening to KZbin audio in mono (99% is just single person dialogue) so your FM signal, demodulated into stereo, was then being made back into mono at my end, so interesting to hear the difference in the different samples, as everything I am hearing is mono. One could be forgiven for thinking, well if converting that signal into stereo added heaps of noise, well make it back into mono to get rid of the noise - does not work that way! Another oddball, feed that demodulated stereo into an X-Y scope, you'd think it would look like any other stereo signal - well it does not, it usually looks quite odd - strange that the human hearing does not notice. Add 1% distortion to an audio signal, often not noticeable on an oscilloscope, horrible to the ear. Turn stereo audio into FM multiplex, totally borked on a scope screen, but totally on to the ear. Go figure.

[@stevie.dx1710]

Hmmm.🤔🤔

[@3rdmm]

Listening to FM in Europe, you'll often use the mono and noise muting switches if you're trying to get stations in other countries.

[@followthetrawler]

I used to be able to hear the 19kHz pilot when I was much younger - drove me mad and kept me listening to AM for a long time. Eventually my hearing got worse with age - now I struggle to hear 14kHz Very interesting video Matt

[@auzzierocks]

I can't hear it now either and I'm 29

[@UHF43]

To my little knowledge, FM audio bandwith is limited between 30 and 15.000 Hz, so anything higher than that should be filtered out before amplification.

[@aritakalo8011]

@@UHF43 Should be and is in modern radios, but take old enough mono era FM radio and it won't have a low pass filter. There was no need for it, since nothing was living over the 15 kHz limit at the time the receiver was made. Hence take old enough FM radio and tune it to stereo channel and the 19 khz will be there to be heard.

[@robertschnobert9090]

​@@aritakalo8011 19khz is pretty high I think. Can a low pass filter be used on high frequencies? 🌈

[@markr9069]

@@robertschnobert9090 A low pass filter can work (up to) pretty much any frequency. 19kHz is a high frequency in terms of audio, but is a very low frequency compared to say 2400000kHz where WiFi and Bluetooth live

[@5HlNOBI]

Theoretically, one could add a "dongle dongle" pre-amp after the dongle output then back to the speakers so that THEN you could have stereo FM on the speakers. Just because it would make a Frankenstein stereo radio that works.

[@Hyxtryx]

That's a good idea. I'm surprised they didn't design it that way, with a line-in jack. Maybe they thought it would cause a consumer revolt. I can see consumers getting upset if they bought a stereo unit that was stereo except for the radio, and then they needed to buy something extra to get the radio in stereo. But if that extra thing is "just for headphones", then it sounds like an add-on device for extra functionality, as opposed to an add-on device just to get the features you thought you paid for. 😄

[@blazingluke]

Loved the bit at the end, cracked me up!

[@strongandco]

Good old Ken Bruce. Glad to hear he's taken at least one listener with him to Greatest Hits. Hopefully many more!

[@malcolmhenderson3866]

I've followed Ken over too. Nice plug for Greatest Hits though.

[@sonickrnd]

"It looks like you’re trying to listen to us from outside of the UK. Due to legal reasons, our streams are not available where you are."

[@StackOverflow80]

I noticed that some portable radios used to have "MPX" output, which is the same like in this Sanyo Stereocast system, so that stereo enthusiasts could use some external stereo decoder. Using add-on stereo decoders, even DIY ones, was quite common in the beginnings of FM stereo. But standard earphone mono output of a mono radio receiver will never contain MPX stereo signal, because it always gets stripped by deemphasis (FM broadcast uses treble boost on transmitter side and opposite treble cut-off on receiver side, to further improve signal to noise ratio). This worked also on older FM mono radios unaware of FM stereo. On this you can see how clever were the designers of FM stereo system, in a matter of forward compatibility. They just didn't leave behind older devices, unlike they do nowadays. They say that stereo reception gives about 20dB worse signal to noise ratio vs. the mono reception of the same station. This is really huge difference. Many stations nowadays choose for mono only broadcasting, because they know, that many people listen radio as background on mono devices or small stereo devices, where speakers don't have good stereo separation. Mono broadcasting allows for lower transmitter output power while maintaining the same range, so that thay can save money (on us).

[@adrienfourniercom]

in France during the 80's and 90's we had "free radios". You can create your own radio by paying your frequency in the FM. Nearly every one of them were mono. Nostalgia, I was listening to them constantly.

[@richcolour]

Are free radios like the UK pirate stations?

[@adrienfourniercom]

@@richcolour They used to be pirate in the 70's, but in 1981 the state opened the FM to avoid the overlap on the waves. Some still exist today, but they are very local. In the 2000, radios were supposed to go numeric, but the licence was too expensive for these little stations, so we still have the radio in analogical.

[@zanegandini5350]

Wow, that Sanyo Stereocast sounds VERY clean for FM radio! Much cleaner than the Sony stereo output later in the video. Goes to show newer isn't always better.

[@reabinc]

- and now I feel the need to learn how FM stereo is encoded on FM mono... Once again, Matt sent me on a trip down the rabbit hole.

[@deathdeathrevolution3499]

I always thought it was just 2 bands that were on different frequencies that did that but this is a far superior way of doing it I suppose

[@ZeusTheTornado]

From what I understood it's kinda like the Quadraphonic signal, it's placed in the ultrasonics and the decoded

[@5roundsrapid263]

@@ZeusTheTornado There was one quad format that was basically FM stereo on vinyl. CD-4, I think.

[@TrevKen]

@@5roundsrapid263 Wait, so is this also how two channel stereo is produced using a single pickup needle of a stylus on an vinyl?

[@5roundsrapid263]

@@TrevKen Not on regular vinyl records. The mono is recorded horizontally, and the stereo separation signal is recorded vertically. A mono needle only detects the horizontal one.

[@neilsradios]

4:20 I did the Alba version of that radio a few weeks back. Alba at the time were just rebadging imported radios but I got a Sanyo Stereocast as shown here and it works quite well. The radio without the adaptor has quite poor sound though.

[@GaryKeepItSimple]

The Standards for Stereo Broadcasting world wide had only just started around then. The UK went Stereo in 73 so it was new technology. (And Expensive) and the public was not very interested like they were for other things. This is from the BBC history website:- Experiments in FM stereo began in the London area in 1958, with an FM Subcarrier system also evaluated. In the end the Zenith-GE system was chosen, helped by the fact that it had already been adopted by the US, and recommended by the European Broadcasting Union. Over the following years stereo became available to the rest of the country. Radios 1, 2 and 4 went stereo in 1973, with a celebratory Stereo Week.

[@joekenorer]

I didn't know I could care so much about a Sanyo record player and the inconvenience of it's sub function FM radio being mono, and then bother buying a tertiary device to convert FM mono to stereo. How tf do you consistently get me involved in some ancient, garbage audio ephemera? This is why I'm subscribed.

[@albinklein7680]

Thank you so much, Techmoan!! I have a Sanyo radio alarm clock since the early 80s (the good one with the flip clock mechanism and sliding pots) and since (literally!) 40 years I wonder, what that "Stereocast" jack on the back of the thing is! And tadaaa, now I know! You are the man!! Greetings from Germany!

[@ThisSteveGuy]

At least you can use one of those corded cassette tape adapters to get stereo out of the speakers.

[@fredbear3915]

Oh yes please, Matt, go on... make that video!

[@hattree]

In the US, channel 6 for television was at the bottom of the FM dial. It was always in mono. I can remember it was the only station that didn't make the stereo light come on.

[@hugeshows]

Hi Mat, I think this thing is what is known as an FM multiplex adapter. It decodes the stereo in the signal so the output of that jack isn't pure audio as you noted... They were common in the early days before FM stereo was popular. At first people weren't sure stereo FM would take off, and lots of regions didn't have any stereo stations. It was a way for consumers to hedge their bets and manufacturers to offer an upgrade.

[@pedrodaniellopesferreira2916]

I believe you are right. I remember reading through an article years ago, stating that in the early 70's the standard for FM stereo was not well established. Yearly receivers came with a phase control to tunne in the pilot signal, just in case it would shift to another frequency in the future.

[@irtbmtind89]

This also would have let Sanyo avoid paying royalties to GE and others for the FM stereo patents for every radio they made. Kind of like how the Xbox required a dongle to play DVDs for the same reason.

[@tortysoft]

My father, a sound man at the BBC, built his own tuner and also bought a demultiplexer. We used to listen the the test broadcasts, BBC TV left channel, Radio 3 on the right. Many years later when I worked at the BBC I occasionally transmitted simulcasts, pics and mono sound on BBC2, stereo on Radio 3, all from my VT cubicle.

[@Astro_War]

Actually a demultiplexer, as mentioned at 2:43

[@sparky6086]

@irtbmtind89 That reminds me of RCA having the patent on superhetrodyne radio. For around 10 years, they didn't allow other manufacturers to use it back on the 1920's. When they finally began to license it to other manufacturers, some of them offered an add on superhetrodyne converter, so the consumer could retrofit their existing radio to superhetrodyne. Rather than getting into the weeds on what superhetrodyne is, in short as a practical matter, it allowed people to recieve many more stations. In early radios, the more powerful or closer stations would drown out the weaker or further away stations, so people were lucky if their receiver could discern 3 stations. With superhetrodyne, they might get a dozen or more.

[@markmarkofkane8167]

That dual pin plug is similar to the plug at the end of a microphone for a portable tape recorder. Large pin microphone, smaller pin, remote switch. (To pause and resume recording and playback) This video is very interesting.

[@UHF43]

The might have looked at their parts bin.

[@dougbrowning82]

Those twin pin connectors can also be found on professional grade headsets. One pin for the mic, the other for the earpieces.

[@gymnasiast90]

This reminds me of my Nokia 6230i. It has a radio app, but it requires a dongle to be connected. This dongle also houses a 3.5 mm headphone port - like with modern phones, they didn't fit one on the device itself. (I eventually bought that dongle in 2022, new old stock. I imagine the people running the webshop I bought it from must have blinked a few times.)

[@tmofee]

The iPod nano was the same, it used the headphones as an antenna

[@nb7466]

My new smart phone as an fm app that you need the headphones plugged in. The headphones are the antenna

[@deathdeathrevolution3499]

Yeah that's how most portable ones work now, unless it's a bespoke radio it usually doesn't have a clunky antenna poking out, although I have seen a version of that for tv before so it was a thing, but it died out in the last decade

[@GoldenCroc]

As others have said, there has to be very few phones around that got radio but doesnt need the headphones plugged in for antenna usage. I have never seen one, certainly not one without some kind of fold out antenna. Maybe there is one..?

[@SeanBZA]

@@GoldenCroc most just need something plugged in, either the charger, headphones or a USB cable, to act as antenna, though there are some that managed to finagle a decent enough (in strong signal areas) antenna into the case itself. Funny thing is that if you buy a phone or device that has multiple world markets, like a mobile phone, media player or such, often the selection of the UI as being USA disables the radio function entirely. Bought a good number of small portable media players, where you can update the firmware on the device, and always select the firmware to be Australasia, as that not only gives you the FM radio, but also CCIR and OIRT bands as well, so many of them will have a FM receiver that will tune from 47MHz to 108MHz with no problem, and stereo is also built in. Pretty much every single Android phone, and every non smart phone, has a FM radio built in, just the US market, for some reason, does not actually enable them. Built into the baseband chipset, has 2 connections for the antenna input and a small local decoupling capacitor, and then all the rest is done internally in the baseband processing, with the audio being there for selection in the chipset. Some might even have RDS as well, but I have not seen that. Often you can also select it as a record input to the media player, even though google has gone on a pogrom of disabling audio recorders on Android, removing that function as part of updates, and removing most of them from the store as well.

[@rikprince8414]

Very nice!! Always interesting to see the workaround that manufacturers came up with. I was a bit surprised to find there are very few bluetooth speakers that were not mono output. :)

[@smvwees]

I found out the hard way :( .

[@deathdeathrevolution3499]

I mean most of the Bluetooth speakers aren't stereo because thats the standard for it, easier to source chips for the standard and buy them than make your own

[@annother3350]

@@deathdeathrevolution3499 he's saying mono is the standard

[@deathdeathrevolution3499]

@@annother3350 that's what I meant but it autod it I'll fix it thanks for making me aware though

[@steviebboy69]

My bluetooth speaker does have 2 speakers in it but it outputs in mono, but it does give a more spacial type sound to it and it is only a cheap one anyway. But it has a JBL boot up sound to it though hehe.

[@conwaytwt]

I have a story from just a few months ago. I was having trouble hearing my local public radio station. The sound was greatly reduced, and what I could hear was distorted. I could almost make things out if I turned the volume way up, but when the next program started, or when the hourly news break came on, the sound was MUCH louder and totally un-distorted. I put up with the bad sound for a few days, then I happened to have the radio on in my car and it sounded fine. I compared to the radio in the house, which was a little SONY ICF-38 portable MONO FM-AM radio. It turns out that the local programming at the station was going through an adapter that inverted the left and right signals, so the MONO signal from the station was canceled out, but folks using "modern" stereo FM receivers were not hearing the problem. When the signal came via satellite from NPR, the sound was fine for everyone. I contacted the station manager (who was unfortunately dealing with a lot of COVID illness) and the next time the station engineer was on site they got it fixed. Fortunately for recognizing the issue, I had just gone through the exact same situation with a church -- their KZbin video of a church service I wanted to hear was completely inaudible on my phone (single mono speaker) but the same audio worked fine on my wife's iPad (stereo speakers). I captured the audio into Audacity and inverted one channel to prove it. A few web searches confirmed that it's very common for a XLR to stereo adapter to get the phase wrong. SO the quick fix is to unplug one channel from the sound board and record the program to KZbin in mono.

[@bluerizlagirl]

My parents used to have a Sanyo Stereocast flip-card clock radio from the 1970s! It had only a mono speaker, but my Dad reckoned there had used to have been an add-on device available that would allow you to listen to stereo broadcasts. He did not have the extra stereo gadget, however; as none of our local transmitters were equipped to broadcast in stereo until after it ceased to be available. So I never got to see it until now!

[@FlowerPowerNZ]

Your observations are bang on. FM stereo is multiplexed at the audio level but needs a lot higher transmit power to work as effectively - compared to mono and all else being the same.

[@RegebroRepairs]

An FM stereo decoder is NOT what I expected from a headphone dongle. 😀 But I did know the stereo signal is encoded into the mono signal. One of our local non-profit radio stations when I was in high school in the 80's wanted to send in stereo, but the municipality said "No, it costs to much to buy a stereo transmitter". So they just encoded the stereo signal onto the mono signal from their studio, and hey presto! they were the only local non-profit radio in stereo! 😀 (They had the Friday evening slot so loads of local teens listened to them while preparing to go out partying, so it made sense).

[@SolitaryWolf]

Absolutely fascinating. I grew up in the 70's and never have come across a device that was so divided for its "parts" to separate FM stereo signals. This must have been when they were just beginning to split the FM signal ever so slightly to achieve the stereo sound and this unit didn't have the FM guts built into it yet. Thank you for sharing!

[@ericpode6095]

I always assumed the mono switch just combined the left/right channels because I never really thought about it. The noise problem now makes much more sense.

[@rog2224]

Some of the Mono DAB stations were in Stereo, but the spectrum was sold out from under them around 2010 for mobile comms expansion. Much like the deregulation of caustic and corrosive substances, it wasn't widely covered outside of specialist publications.

[@GodmanchesterGoblin]

To be accurate, the spectrum that they were on is still used for DAB. In fact, the DAB frequency blocks used by the multiplexes have not changed or been reduced, more multiplexes have been added. It was the multiplex operators that decided they needed to sell the space a second time and so they added more stations to each multiplex. Since a single multiplex is always 1.536 Mbits/second, they can carve it up how they like. DAB actually allows the bit-rate usage for each station to be changed every s seconds, but most only change a couple of times a day if ever (mainly BBC R4, etc).

[@AdamG1]

Several local stations have added HD Radio streams and it's brought back the days of switching between mono and stereo to get a clearer signal if you're moving around. When you're driving in fringe areas it's pretty irritating when it keep switching between HD and standard radio. One reason I use XM most of the time

[@B3tanTyronne]

As much as I like the dongle (oh matron etc), the death star droid looking combi at 5:42 with the light show looks interesting.

[@maxx9137]

Dude, I love your outro so much. The chill music with all those cool clips you show is awesome.

[@PascalGienger]

I always wondered why a recorded radio show at 19cm/s had a constant tone when played back at 9,5 cm/s. Sure enough that radio didn't have a low pass filter to remove the stereo pilot tone and the higher frequencies... The pilot tone by the way is not only there to indicate a stereo transmission but - as it's done with the same quartz in the emitter - it is always exactly 1/2 the frequency of the actual stereo difference signal - which is broadcast without carrier. So a small pilot tone is sufficient to create the 38kHz carrier in the audio signal. Later came RDS & Co at 3x yhe the pilot, 57kHz.

[@rogerduerden373]

I can remember in the 70s and 80s when Radio 4 was normally broadcast in mono, but on rare occasions they switched to stereo for specific programmes.

[@jimb032]

I about spit my tea out when you popped the lid off of it. I was thinking "does it even have a circuit board, or it's a dead bug circuit squashed into the case?!" I like the whole thing pretty neat. I wouldn't want it as my only unit to listen to, but it's very 'flashy" and lets agree that there are things made that were 10,000 times worse. You made the video about Kenwood being the king of budget hifi, but Sanyo (or PanaFisheYo as I call them) made some seriously nice stuff in the day. Mono/Stereo switches were great in the day when the signal was not quite good enough for stereo but often times the mono switch made it very tolerable and listenable. (vs the stereo flipping in and out annoyingly) But I never knew that there was a type of NR that was available in mono that was not in stereo -very interesting! Thanks for the great video as usual!!

[@CraigRodmellMusic]

New Zealand, where I live, only got FM in 1983, and that was only for the Concert Programme (which plays classical music only). Commercial radio only got FM in the late 1980s. I read a story once of someone who was emigrating to New Zealand from Britain in the late 70s or early 80s. They'd asked if New Zealand had FM, and was told that we did. So he brought his expensive stereo FM tuner with him over to New Zealand, only to find that the only things it would receive were Japanese fishing boats and the police! And like I was saying, for several years after FM was introduced, it was Classical music only. Everything else was AM. One of my all time favourite radio programmes was a BBC series called My Music. This was normally played on non-commercial AM radio here, but at one time, it was also broadcast on the Concert Programme in FM stereo. It was only when I heard it on stereo FM that I discovered that two of the contestants, John Amis and Ian Wallace were panned hard left and hard right respectively, solely. The other two contestants, Frank Muir and Denis Norden were panned half left and half right, and the Chairman, Steve Race was panned centre. It made for quite a different listening experience from what hearing the same programme in mono had been.

[@aeroping]

NZ had commercial FM stations earlier than that. Among many others I could mention, 89 Stereo FM and Magic 91 FM started in Auckland in 1983. From 1982, Wellington's 2ZM did occasional temporary FM broadcasts during trade fairs until they became ZMFM permanently in 1985. Prior to this, there were pirate FM broadcasts in Auckland around 1981. Wellington student station Radio Active began broadcasting in FM stereo in February 1982. In some places you could pick up TV audio on the FM band. A good way to record music or comedy programme soundtracks before VCR recorders became more affordable.

[@dansheppard2965]

The first truly legit use for irritatingly repetitive radio jingles, 😀. Something else that the dongles could help with is brand loyalty. If you get the dongle for your Sanyo suitcase thingy, you'd feel more like getting a Sanyo-branded portable radio thingy, it would be cheaper and you'd feel less stupid for having one kicking around.

[@SeanBZA]

I would also say this was done to avoid paying royalties to the owners of the FM stereo rights holders, GE and Zenith, so instead developed the low cost stereo adaptor, so that only those who wanted stereo would buy it, and thus the royalties would be only based on the low cost module.

[@rEdf196]

Like that Sanyo proto-dongle radio twin plug, dual micro and 1/8 inch plug combo's were common place for tape recorder microphones in the 1960's to mid 70's the main 1/8" plug was for the mic itself the tiny 1/16" plug was for turning the tape player on or off. As a young 70's kid, I loved flicking the switch on and off while talking on the mic with cassette recording, then play it back with my voice pulsing squealing and pitching up and down.

[@airplaneengine]

I have a local FM station that cuts their stereo pilot when the content is mono, such as when only the DJ is talking. They do that to lower the background noise when it would be most noticeable to the listener. That used to be more common decades ago, I don't see that much anymore. Just wait until you go down the AM-stereo rabbit hole.

[@ppotter]

When I used to record things from the radio in the 90s - albeit mainly comedy shows - I always used the mono as stereo round these parts was terribly whiny and hissy. Mono was crystal clear. And as soon as I typed that you mentioned it. Ha!

[@Darxide23]

Quick nitpick about terminology. Whether the stereo switch is on or not, you're always demodulating the signal. The M in AM and FM stands for Modulation. You have to demodulate the signal to get any sound at all. What you're doing when you split the stereo signals out of a single mono broadcast is _demuxing_ the signal. Or it may be known as _demultiplexing_ instead. Muxing is just shorthand for Multiplexing. You'll see this rarely on a piece of old stereo equipment as an MUX or MPX switch setting. Anyhow, it doesn't change much. Everyone understood what was meant. Just thought I'd toss it out there.

[@Stevedd33]

Wow! This really brought back memories. I'd forgotten that I used to have one of these. I bought it to go with my Sanyo clock radio as I was obessed with the idea of listening to things in stereo. Of course the station that I wanted to hear in stereo the most, BBC Radio 1, would continue to be AM only for many more years. Thanks for this. I really enjoy your channel and watch every video.

[@dong6839]

I saw a briefcase device like this back in the 80's (made in the 70's) that had a built in FM transmitter! It was designed to allow you to broadcast your own little party, and all your guests would tune their car radios and portable radios to a particular frequency, and they would all hear whatever you were broadcasting (from the built in record player, or a plugged in mic, or line level input) it even had a simple mixer built in, so you could professionally "mix" your music with your voice or an external set of turn tables plugged into it etc. It was like an entire low power radio station in a briefcase. It was advertised for use at drive in theatres, beach parties, race tracks/drag strips etc, where you couldn't set up an entire public address system. There was even an external accessory sold for it to be completely powered off-grid. Not sure if it used a car battery and some sort of antiquated 12V inverter (not sure if they even had those back in the 70's) but it claimed to allow you to be able to use the transmitter in remote locations where you didn't have access to a power outlet! I can't remember who manufactured it, I want to say I remember seeing Realistic on it, but that could just be fabricated by my childhood memories of seeing shiny stainless steel switchgear and high end equipment and associating that logo to it.

[@jmulvey371]

Your last point about DAB radio stations choosing to degrade their signal in order to squeeze more content into the same bandwidth is an important one. Much like the transition to over-the-air digital tv in the US, what was touted as high-resolution signals becoming available for free has now become worse signal quality than what we had before. And the major cable and streaming services control the only valuable content anyway.

[@tgheretford]

Quantity, not quality, sells radios. DAB only took off when the BBC created new digital radio stations and the choice of stations increased as bitrates decreased. An unfortunate and uncomfortable truth to us who want good quality audio but most people listen on a cheap single speaker radio in a kitchen or a workplace where high fidelity doesn't matter.

[@jmulvey371]

@@tgheretford Over here I'm not even so sure it's about selling radios, per se. The real money is in content creation, and the way our corporate content creators have chosen to go about it is through market segmentation. Television broadcasting via a public license has become the home of home shopping network, christian broadcasters and old tv programs that cost little or, in the case of shows that are in the public domain, nothing. That is, it's low-end broadcasting for poor people. Anyone with a little money to spend is upsold into cable or streaming or something else, where the decent content lives. (Nowhere is this more repulsive than in the world of professional sports, where fan loyalty is converted to cash in the most aggressive and cynical way possible. Today in America, it's become impossible to be a fan of a pro sports team on a low-income budget. Revenues for the team owners, naturally, are higher than than they've ever been.) And, as I said, those net-based categories of broadcasters are almost entirely unregulated in the US, as opposed to over-the-air, which at least has to show some semblance of acting in the public interest. (Don't ask me how home shopping network qualifies.) I'd like to hope that the UK is incrementally better, but I'm probably kidding myself.

[@leamanc]

Fascinating stuff! I always thought the FM mono/stereo worked like that but I had it reversed. I assumed it was a stereo signal but that the receiver stripped out some signal to convert to mono. As an aside about one-speaker radios, my C Crane one-speaker radio has a switch for: speaker, mono out to headphones, and stereo out to headphones.

[@stevie.dx1710]

I have a CCRadio SW and a 2E. The SW has no blending and a stereo/mono switch. Oddly, the single built in speaker plays one of the channels when set to stereo, with all it's inherent noise. The 2E has a stereo threshold and puts itself in mono as the signal weakens. What model do you have that switches the headphone jack like that?

[@cocotoni1977]

My dad has produced a quite similar add on to listen to stereo output on what was originally a mono radio set for his bachelor thesis in ‘71. Having grown up in the ‘80s myself when the radios all has stereo built in I never understood the concept fully. Having seen it now as a product, well now it clicked. Thanks Matt!

[@fosterb247]

Super entertaining and informative as always Mr Techmoan - Thanks

[@markelliot1248]

Hi Matt, Interesting stuff there. I would recommend for demonstrating FM one of the small FM transmtters intended for use in cars to take a MP3 player output and sending it to the car's FM radio. Only a few quid and would allow to to play some of your royalty free music through the receiver.

[@patrickalvino5544]

Great video as usual, Techmoan. Interesting topic of FM stereo. I have in my collection an AM/FM tuner from the 1950's labeled as "stereo" although this was well before the multiplex system of FM stereo broadcasting was adopted. It can output AM and FM simultaneously to different amplifiers and speakers. Although it was a bit before my time, I understand that some radio stations that had both AM and FM signals, would occasionally broadcast the right channel on say, the AM station and the left channel on the FM thus creating stereo broadcasting. Clearly this wasn't ideal as fidelity and reception would differ between AM and FM and of course, if you only have a normal radio, you are only getting half the signal, but it was rather ingenious nonetheless. Best wishes from across the pond.

[@willyarma_uk]

If you sample the FM mono into your computer at 192KHz and then look at it with a spectrum analyser (I use GoldWave for this, I assume Audacity has this also?) then you can see the whole FM MPX with pilot tone, stereo difference and RDS data.

[@dougbrowning82]

If you're tuned to the right station, you might also see the SCA carrier. SCA is a method of delivering environmental music to public areas, like shopping malls.

[@stevie.dx1710]

@@dougbrowning82 SCA is still a thing?

[@dougbrowning82]

@@stevie.dx1710 In some markets. I remember seeing a video of an SCA radio on KZbin about a year ago. Was a regular GE FM radio with an SCA board added.

[@MrBrainFear]

I absolutely love this channel. Great video.

[@williamford7013]

Never been so excited to listen to a radio station on the other side of the world

[@AttilaSVK]

The difference between mono and stereo FM broadcast is due to the fact that the sound of a radio station has been processed heavily, including stereo image widening. That makes the mono reception sound worse than it should without such processing. Also, if you have a sound card capable of 192 kHz sampling rate (with a low-pass filter tuned high enough to let through about 60 kHz), you can use the multiplex audio output of the Sanyo to feed the signal into a computer, and for example, extract the RDS information from it using an application called RDS Spy. There's a video on my channel doing an FM band scan with my Revox B260 tuner with the MPX output (one of the scope outputs) hooked up to my sound card, and decoding RDS on the computer.

[@TheLoxxxton]

As always, answering the questions I didn't know needed asking!

[@leathere1]

Brilliant, thank you. I now feel very old. I had a Sanyo stereocast dongle with the smaller portable radio and matching headphones.

[@tararenemartin]

Thanks Mat; you’ve taught me something new yet again! Love your work! 👍🏻

[@skylined5534]

I had no idea so I'm glad to be taught stuff like this from someone like Mat 😊

[@klipkultur3680]

40 years ago I was wondering about that mysterious stereo thing and now I know. Thanks Techmoan!!!

[@boardsort]

Excellent ending! I like what you did with the Deja vu bit. Very creative.

[@bslaws]

In 1958/59 my father was in England and purchased a Quad amp, preamp and single ESL-57 electrostatic speaker. When he moved back to the US in 1960, he bought another amp and another speaker so he could have stereo. I remember the original brochure showing a single ESL-57 sitting in the middle of the room as at that time, mono was the thing. He also had a Garrard 301 turntable. He had good taste.

[@neontime]

Professional receivers used in the broadcast industry usually have that output available on a BNC type connector. It will be labeled something like "multiplex", "mux" or composite. It is used in repeater setups to feed a transmitter directly without having to decode and re-encode the stereo signal. The composite output also carries the RDS data channel..

[@rodneyarnoldi]

I like the little sony XDR-S41D radio, could be useful when I'm on holiday, especially having the wake-up facility, although £60 seems quite expensive.

[@Techmoan]

I bought mine when it was in the 'middle of Lidl' and while I can't remember the price I'm pretty sure it was £40-odd

[@razeel2000]

I own this radio and I am quite happy with it. One thing I'd like to mention is that the wake-up alarm only works when it is connected to the power supply. When running on the batteries, it is disabled.

[@Techmoan]

Did it come with a power adaptor, I can’t remember. If it did I could do with finding where I put it.

[@razeel2000]

@@Techmoan Yes, it came with one. Model AC-P5005F

[@marksweetman8765]

Very informative. I’d always assumed fm was stereo broadcast. You learn something new every day

[@NewCityMedia]

Great video. The Sanyo 'dongle' reminds me of the stand-alone stereo decoder boards you could buy in the electronics hobby shops in the 1970s. You could literally easily hook them up to virtually any mono FM radio, even the cheapest of portable budget sets, and produce a stereo output, as virtually all FM receivers pick up the stereo pilot tone as it is embedded in the mono signal anyway.

[@manoflego123]

I never realized FM was in stereo because I just listen to the news most of the time, but I do have a little '80s era GE alarm clock with a switch to enable and disable FM stereo. It also has a headphone jack, because there's only one speaker regardless of if the signal is in stereo, and the difference is remarkable. It almost sounds like the music is coming from "inside" your head instead of through your ears when you switch to mono.

[@manoflego123]

This little alarm clock picks up really clean FM stereo compared to what you've got in this video, but I don't know if that's a result of American FM differing from UK FM at all.

[@martin-uz1py]

That Sanyo RP7-1200 spherical record player looked interesting. Informative video as usual I had never thought about this myself.

[@fearlessjoebanzai]

*RPT-1200 It says it is a lightshow in the globe! I'm sure Techmoan would go Techmad for that!!!

[@JonFether]

I saw that thing listed and my attention was immediately drawn to it as well. I went fishing through the comments just to see if anyone else called it that RPT-1200. It may or may not be technologically interesting but for sure a great period piece. Hope Techmoan happens across one someday.

[@martin-uz1py]

@@JonFether Etsy has one for £1,008.23 but that is quite steep for a novelty.

[@DeneF]

That was our family stereo in Manchester for the mid/late 70’s. I was only early teens and so don't remember if it had that strange line out malarky and I know my mum and dad wouldn't have. Lol. Just the sight of this takes me back. Big smiles. Many thanks.

Superbe video!!! Thank you from a radio gentleman from Patagonia Argentina

[@SidewaysCytlan]

What a strange device. How does it derive a stereo signal from a mono signal? Demodulation is pretty interesting stuff. Weekend rabbit hole!

[@MrDuncl]

The stereo is there as ultrasonics along with the mono signal (as is RDS these days).

[@10p6]

Here in the USA, we have FM, FM Stereo, then HD version of the same station, and then Sub channels in that same HD frequency, with the most I have found so far as 4 sub channels on one FM frequency. Hmmm.

[@barrieshepherd7694]

A lot of US stations also had a sub carrier carrying low grade 'MUZAC' for use in lifts etc.

[@derek20la]

@@barrieshepherd7694 That would be SCA services. Subcarriers at 67 and 92 kHZ.

[@veb6814]

Another awesome video from Techmoan!

[@tvamsterdamonline]

This is a great issue! Great work Techmoan. I love your films!

[@mikesbarn1858]

Here in the US we also used the 67 Hz and 92 KHz modulation signal for extra channels. It used the bottom and top 10% of the modulation wave.

[@marcusdamberger]

Yup, they used to use the extra audio at those frequencies for services like a reading service for the blind, i.e. radio programs to read the newspaper and other sources of information, or I even think some audio books too. Usually offered on NPR stations. But you had to have a special radio that was modified for SCA service, or Subsidiary Audio. Some commercial stations would offer elevator music or services like Physicians Radio Network for doctors offices to have "commercial free" music, and I think sometimes grocery stores would also use similar services. But of course they had to pay a fee, and the special radio tuner was provided. Nothing stopped someone with a little knowledge to build a SCA decoder and hook it into the FM detector portion of the radio before all that got filtered out. Fran Blanche of Fran Lab did a video on the SCA receivers kzbin.info/www/bejne/rXO2e4eAmKaHl5o In later years, they put paging services on those subcarriers and the radio station got paid for by the number of pages that went out. Then RDS was finally added in for Radio Data System for program information like Song and Artist to display along with other possibilities like telling the radio what other frequencies the station is available on if the current one gets weak to auto switch. But that is mostly popular in Europe where one network is on multiple FM transmitters filling in signal gaps in mountain ranges etc. Or using the RDS to tell the receiver to turn up the audio louder by a few dB for weather announcements, or news. I've heard that in Germany with the car radio turned down to background levels, then suddenly it pops up louder for 30sec while they tell you the forecast or news and then it dips back down in level to where you had set it at. In the U.S. they never seemed to use these options at all even though it's in the standard. But radio head units are not all equal.. They don't even to this day display all the information the same way even though screen real-estate has expanded while radio stations are all over the place with RDS data. Some seem to cram everything into one line and truncate text, or put their slogan only, or do some single line slow text scroll that's useless to read while driving.. RDS just seems badly implemented in U.S., while it seems way more consistent with what I've seen in Europe.

[@fflynnful]

Those subcarriers are used for RDS. In the old days, before 1990 or so, muzac was at 67khz on a lot of FM stations.

[@mikesbarn1858]

That was my point. I worked for Muzak tuning and repairing SCA receivers. I haven't seen one of those in 35 years.

[@leefrohock]

Wow, you have a Hitachi TRK-8290E. I had one of those in 1981 and it cost me £179. I always regretted selling it but to buy one now with a working tape deck is near on impossible. very complex inside too as i recall. Love to see you do a Video on it in the future as i really miss it. Fantastic sound it had too :D

[@lidbass]

I bought one in 1983 to take to university with me. Got it from Curry’s and I seem to remember it cost £120. The tape broke exactly one week after the guarantee ran out, but in those days there were strange things called ‘repair shops’ where it went for a holiday for a week or so. It then worked perfectly for years until, sadly, it was stolen. Would love to have another but a) it would just be to soothe the nostalgia and b) as you say they cost a small fortune and you can’t guarantee they will work properly. They were incredibly beautiful, though.

[@darrenerickson1288]

That's a fantastic bit of arcana. Thanks for sharing it and brightening my Saturday!

[@richardthompson6690]

Really enjoy your show! I didn’t know about the FM stereo/mono differences. Very interesting what you cover!