FM technology

[steveu]

Modern FM

FM stereo is a very old and well established standard. Years ago, the 200KHz bandwidth was used to sell "Muzak" on subcarrier frequencies, to department stores and elevators. Muzak - Wikipedia
Mathematically, a subcarrier is not different from an additional transmitter, but uses only one transmitter.

However more recently most FM stations include "HD radio" which stands for Hybrid Digital, NOT high definition. HD radio is compressed digital that reuses the subcarrier bandwidth.
HD Radio - Wikipedia

Modern radio also includes low speed data "RDS" (Radio Data System), not to be confused with "SDR" (Software Defined Radio). Radio Data System - Wikipedia

There are a number of SDR FM tuners on Amazon.
SDR-Radio

Bottom line is that modern radio systems make classic FM stereo look very primitive, although nothing like as complicated as 4th gen cell phone systems. Of course you will have heard a lot about 5th gen wireless but I have a book on 4G that included articles from 40 authors, most of which is over my head. These things use math that most people don't know exist.

 

[stocktrader200]

The old pioneers sx-780 and sx-3700 have the ability to deliver better then DAB ( 160kps) FM performance. 82 db s/n stereo and .05% distortion after the tuner section is upgraded with power supply isolation and op amp filter added.

 

[DF96]

One could generate 2 carriers by phase modulating by the difference frequency: only one transmitter required.

Phase or frequency modulation creates infinite sidebands. Better to use AM to generate the two carriers - or just do it all digitally.

This "primitive" FM stereo system is still the source of the highest quality broadcast sound you are likely to hear. Digital systems used properly could just surpass it, but almost everywhere they are not used properly so the sound is worse than FM.

 

[dhaen]

Phase or frequency modulation creates infinite sidebands. ...

Yes that's a "feature" of FM modulation. However unlike the audio modulation, we would know the precise positions of the sidebands. It would then be possible to interleave them with the sidebands of adjacent channels as used to be done on UK VHF TV.
Anyway this is all nonsense because we are where we are

This "primitive" FM stereo system is still the source of the highest quality broadcast sound you are likely to hear. Digital systems used properly could just surpass it, but almost everywhere they are not used properly so the sound is worse than FM.

UK FM is certainly far superior to our DAB transmissions but don't forget that the major stations are also transmitted on satellite and terrestrial TV multiplexes, and at a decent bit-rate. I've been impressed at the quality.

 

[MarcelvdG]

Down here, no matter what modulation type is used, the vast majority of the radio stations sound horrible due to excessive dynamic range compression.

 

[davidsrsb]

I agree with DF96. You can just add the signals of two modulators and pass them through a common PA. It's a pity that the signal is no longer constant envelope, which complicates PA design, but the same holds for AM broadcasting and analogue television (as well as DAB and DVB-T), so that wouldn't have been a showstopper.

Efficiency would be MUCH worse. I have seen FM transmitters reaching 76%
DAB is more like 25%