Muzak worked best where recording performance fees were well enforced. Where an agent would visit your store or office and if you were playing canned music (record or radio) to the public, they would sue you. There is a long history of fee-enforcement in the US. Laws and fees will be different in other places.
Also despite making money, the US Muzak company was often an orphan. 2009 it went bankrupt, and emerged significantly reorganized.
SCA was only one of multiple technologies. Muzak started on wires before radio. Even through the radio period they leased a lot of phone lines (and store-size PA amps had an optional phone-line interface). Today it is on the internet, though there may be legacy installations on SCA or wired. Wikipedia says Muzak has re-named as Mood (MOOD:MEDIA), but I don't find much about them. The racket in my local supermarkets is NOT Muzak but grating oldies on very tired speakers......
I read in FM books like the RCA that in the past, there were fax transmisions using subcarriers in FM normal channels. How extensive were they used and if currently is there anyone?. I suppose that when digital comms grow up, those systems became obsolete. I never heard such a thing here, in the *** of the world.
The "fax on FM subcarrier" has been patented: https://patents.google.com/patent/US5790268A/en
Apparently, the use of subcarriers has been deregulated in the US so (don't laugh!) it's forbidden to use a tunable subcarrier receiver. Usually that's the best incentive for the DIY crew to get active 😉
https://www.fcc.gov/media/radio/subcarriers-sca
Apparently, the use of subcarriers has been deregulated in the US so (don't laugh!) it's forbidden to use a tunable subcarrier receiver. Usually that's the best incentive for the DIY crew to get active 😉
https://www.fcc.gov/media/radio/subcarriers-sca
Dear friends. Please let me leave some questions:
1.- If the FM chanel (theoretically and legally) has 200KHz BW, which would be the optimum IF BW? regarding future stereo adaptor. Discarding selectivity in the RF amplifier, because doing some aproximations, with a center frequency of 100MHz and a very good Q of 100, then the RF BW is roughly 1MHz or 5 channel width.
2.- When you said that proper BW for FM stereo is 312KHz, is it the entire IF + FS detector BW or the FS detector alone? And in such latter case, with a IF BW of 200KHz which is the advantage?
3.- When say those 312KHz, are they between FS peacks (positive and negative)?
Again, let me some patience. I am learning step to step.
Kind regards.
1.- If the FM chanel (theoretically and legally) has 200KHz BW, which would be the optimum IF BW? regarding future stereo adaptor. Discarding selectivity in the RF amplifier, because doing some aproximations, with a center frequency of 100MHz and a very good Q of 100, then the RF BW is roughly 1MHz or 5 channel width.
2.- When you said that proper BW for FM stereo is 312KHz, is it the entire IF + FS detector BW or the FS detector alone? And in such latter case, with a IF BW of 200KHz which is the advantage?
3.- When say those 312KHz, are they between FS peacks (positive and negative)?
Again, let me some patience. I am learning step to step.
Kind regards.
(1) is impossible, for a start. The maximum deviation is 75KHz, which gives broadcast BW of 150KHz. This causes sidebands, which means you need more BW at the receiver, namely 312KHz for full stereo, if my calculations are correct. You may also want to build in narrower bands imto the IF strip, say 240, 200, or even 150KHz, user selectable, for difficult reception conditions or remote stations, but you don't do that at the detector. I would go for 400KHz there.
It might be enough to read the specs of commercial filters, applied in FM radios.
1) https://www.rf-microwave.com/en/rf-band-pass-filters/553/
2) https://www.rf-microwave.com/en/fm-discriminator-filters/405/
Long ago, Toko even produced a "linear phase" 10.7 IF filter for "top end" receivers - I think it had a ~300 KHz Bw.
When living in Europe, even a 150 KHz wide IF would be satisfactory for weak signal reception in the presence of strong adjacent channels because in some places channel spacing could be just 100 KHz.
Here in Centrla America, many stations are producing signals that leave no other conclusion than that m=7.
So the ideal is continuous variable Bw (as in that patent) or compromise, based on preferences depending on "most appreciated stations".
1) https://www.rf-microwave.com/en/rf-band-pass-filters/553/
2) https://www.rf-microwave.com/en/fm-discriminator-filters/405/
Long ago, Toko even produced a "linear phase" 10.7 IF filter for "top end" receivers - I think it had a ~300 KHz Bw.
When living in Europe, even a 150 KHz wide IF would be satisfactory for weak signal reception in the presence of strong adjacent channels because in some places channel spacing could be just 100 KHz.
Here in Centrla America, many stations are producing signals that leave no other conclusion than that m=7.
So the ideal is continuous variable Bw (as in that patent) or compromise, based on preferences depending on "most appreciated stations".
OK. Things are clearer now. Thus for a first try, I shall go for 200KHz at the IF. Having into account the large quantity of stations close to me (say 1Km or 2), with more BW I have suspicion of large splatters (as we call in ham radio) will be present. I was searching in the internet the datasheets for the MuRata IF filters widely used in ss receivers, and they go from about 180 to 280KHz. In any case, when building the decoder, if I find it is too narrow, and as the trafos's secondary will not be glued to the coil former, I can re-adjust them further.
The tower below depicted is only 800m far from me 😡.
The tower below depicted is only 800m far from me 😡.
Attachments
The discriminator filter usually is wider than that for the IF. Compromise with wider discriminator is linearity vs lower audio output, only an issue for commercial sets.
I counted 8 vertical dipoles on that tower so it's unlikely to be "just local coverage". It reminds of the AFN Europe station at a few Km distance from my house in the Netherlands. 100mV at the receiver input, on commercial sets AFN was "all over the dial" and at the time there were no cheap solutions. I managed a front end with a BFT66 at 10 mA followed by a single ended chopper mixer (A few V of LO on g1 of a 3N211, signal at g2) which was surprisingly linear also according to (no longer available) datasheet so I could receive even Eastern German on a daily basis.
I counted 8 vertical dipoles on that tower so it's unlikely to be "just local coverage". It reminds of the AFN Europe station at a few Km distance from my house in the Netherlands. 100mV at the receiver input, on commercial sets AFN was "all over the dial" and at the time there were no cheap solutions. I managed a front end with a BFT66 at 10 mA followed by a single ended chopper mixer (A few V of LO on g1 of a 3N211, signal at g2) which was surprisingly linear also according to (no longer available) datasheet so I could receive even Eastern German on a daily basis.
What do you mean by m?
I'm used to it meaning modulation index, that is frequency deviation divided by modulating frequency, but the modulating frequency can be anything from 20 Hz or 40 Hz up to 53 kHz for FM stereo.
When I was a kid, I built the SWTPC FM SCA adapter and actually got it working. The elevator music thus received didnt exaclty fit my musical tastes at the time, so it was not money well spent... One would think I would have thought about that before purchasing!
Correct, I'm using m for modulation index. For m=5 and max audio frequency 15 KHz (no stereo) 180 KHz IF would be sufficient. Most available mass-produced FM sets here are fitted with a few IF coils (no BPF) and can cope with a much larger modulation index, motto "louder is better". From the observed spectrums of mono stations I could verify that larger m.
It looks like a well designed circuit. Hardly anyone could expect elevator music as that might annoy shoppers. A comparable experience I had in this region: there's more chatter on FM channels than on MW - the opposite of what I was used to in Europe.
So you mean the frequency deviation divided by 15 kHz, m = 7 then means that the frequency deviation is 105 kHz.
Indeed, it's what many of the spectrums are suggesting, confirmed by comparison with output of signal generator (Marconi Instruments 2022A).
I know some radios are designed to handle deviations up to 150 kHz without gross distortion because the 75 kHz isn't enforced everywhere. Over here you get a fine when the transmitter spectrum gets outside a given spectral mask (Stokkemasker).
That would explain a lot. When living in Tenerife (Spain) some African stations were using a deviation too high for the receiver I designed and used in the Netherlands, functioning well for all stations I could there.
Here fines can be applied after having filed a complaint concerning suffered damage. Panama has a govt. operated dept. (ASEP) that verifies a complaint, then deals with the accused corporation (no matter the size). Clue is your ability to supply verifiable observations / measurements / conclusions. So recently, thanks to ASEP, MW and SW were "cleaned" from strong broadband interference from a solar plant of the power company. Osvaldo might encounter similar issues on FM.
Nowadays it is exactly the way you were used to, at least in Germany, where AM vanishes silently. One has to carefully pick FM stations without annoying charts fodder and babbling presenters.
Best regards!