Raspberry Pi FM Stereo Transmitter...

[Mark Hennessy]

As regards FM bandwidth; we often see the BBC spec of 15kHz bandwidth quoted, but how many dB down is it at that point? What sort of filtering is used, any phase EQ, turnover frequency, all that?

You've heard of NICAM, I assume?

[ppppenguin]

Don't know how it's done now but at one time the feed to FM transmitters was done with a 13 bit pcm system at 32kHz sampling. Even with a perfect implementation this could not have been flat to much more than 15kHz and fallen to zero at 16. This still exceeded the required performance of the FM transmissions.

[Mark Hennessy]

Prior to PCM, the audio quality of FM broadcasts was a matter of geography. Fine if you lived in the south-east

NICAM replaced PCM some time in the early '80s: http://www.audiomisc.co.uk/BBC/PCMandNICAM/History.html

It's still NICAM today: http://www.bbc.co.uk/rd/blog/2016-01-35-...ot-dot-dot

Not everyone realises that NICAM was not invented for adding digital stereo sound to analogue TV, but there it is. NICAM 728 is very similar indeed to NICAM 3.

Of course, NICAM is 14 bit, 32kHz.

As for going beyond 15kHz, there's the small matter of the 19kHz pilot tone...

[ppppenguin]

And 38kHz subcarrier for the difference signal. Plus 67kHz storecast in the USA.

[Terry]

Plus 67kHz storecast in the USA.

Isn't that what is used for RDS in this country?

[Cardigan]

As regards FM bandwidth; we often see the BBC spec of 15kHz bandwidth quoted, but how many dB down is it at that point? What sort of filtering is used, any phase EQ, turnover frequency, all that?

You've heard of NICAM, I assume?

Yes. And before you ask, I am aware of NICAM-676 and others and what NICAM stands for, so please don't attempt to patronise me.

[Mark Hennessy]

Plus 67kHz storecast in the USA.

Isn't that what is used for RDS in this country?

RDS is 57kHz (3rd harmonic of the 19kHz pilot tone).

Details of the SCA that Jeffrey is thinking of: https://en.wikipedia.org/wiki/FM_broadca...r_services

[Cardigan]

And 38kHz subcarrier for the difference signal. Plus 67kHz storecast in the USA.

Many years ago, Signetics published within the data sheet of the NE565 an SCA decoder circuit using said PLL.

[Mark Hennessy]

As regards FM bandwidth; we often see the BBC spec of 15kHz bandwidth quoted, but how many dB down is it at that point? What sort of filtering is used, any phase EQ, turnover frequency, all that?

You've heard of NICAM, I assume?

Yes. And before you ask, I am aware of NICAM-676 and others and what NICAM stands for, so please don't attempt to patronise me.

I'm not trying to patronise you, and I strongly resent the accusation.

How was I to know whether or not you already knew about NICAM? I suspected you might, but I'm entitled to check before typing a much longer reply, right?

So in which case, you already know the answer to your questions (or at least, you know where to look for the answers). So was it a rhetorical question? And why?

Bluntly, you've poured cold water on an interesting topic, and done so in a rather unfriendly fashion, which is against the rules set out for the use of this forum - I draw your attention specifically to this extract:

Posts that contain significant negativity without moving a conversation forward are discouraged.

Hopefully we can now return to the topic.

[`FRANK.C]

You need an objective - a project - else you'll just faff about and get nowhere...

That's a very good point. I got a Pi a couple of years ago but never really did anything with it. It's lying in a drawer somewhere now.

Frank