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Old 22nd Sep 2018, 8:02 am   #21
Ted Kendall
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Default Re: FM stereo

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The PLL-based decoder also had the advantage that it made things relatively easy to implement that all-important feature: a light that comes on when receiving a Stereo signal!
The stereo pilot tone appeared on some Radio 2 transmitters weeks before the stereo programme feed in 1972. Several people rang the BBC to rave about the wonderful stereo sound...
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Old 22nd Sep 2018, 11:06 am   #22
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I seem to remember the Beeb used to make a point of turning the tone on and off depending on the source material, at least in the early years?
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Old 22nd Sep 2018, 11:23 am   #23
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Default Re: FM stereo

I may have mentioned this here before but a good story is worth repeating. In the early days of stereo on R2 a call was put through to us in London BH Control Room and the caller asked why the news was just read from her kitchen when she normally heard it in her lounge - the puzzled Assistant Tech Ops Manager buzzed my colleague manning R2 Continuity asking if there was anything unusual about the news transmission and he confessed that he'd been playing around with the pan pots but forgot to reset the news to centre prior to fading it up hence it was broadcast panned hard over to one side, We concluded that the listener had one speaker of her stereo in the lounge and the other in the kitchen!!

Regarding the stereo pilot light I used to amaze people by telling them part of my job was to simultaneously turn a light on in homes all over the country with the press of one switch.........then their amazement would wane when I explained exactly what I meant.

Happy days!!

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Old 22nd Sep 2018, 11:28 am   #24
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Default Re: FM stereo

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I seem to remember the Beeb used to make a point of turning the tone on and off depending on the source material, at least in the early years?
We certainly did that on R3 as mono gave a better signal to noise ratio in fringe areas.


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Old 22nd Sep 2018, 11:49 am   #25
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Default Re: FM stereo

The much worse signal to noise ratio of stereo fm radio and just R3 did not help its early adoption, many were used to the built in aerials of radio’s and radiograms which in good signal areas worked well. Generally with the technology used it was not good enough for stereo and required a proper aerial. Some customers didn’t want or couldn’t have another aerial.

When stereo transmissions were more common, audio seperates and music centres were in the shops and we had much less of a problem selling a good aerial to go with them.
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Old 22nd Sep 2018, 11:54 am   #26
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Default Re: FM stereo

Some networks at least used in band tones to switch between stereo and mono. From memory these must have been about 10kHz and were clearly audible on half decent equipment. This would have been in the 70s and 80s.
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Old 22nd Sep 2018, 12:16 pm   #27
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Default Re: FM stereo

At the BBC the pilot tone frequency was 19Khz and this was certainly audible with a half decent system and young ears.

https://en.wikipedia.org/wiki/Pilot_signal

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Old 22nd Sep 2018, 12:24 pm   #28
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Default Re: FM stereo

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Some networks at least used in band tones to switch between stereo and mono. From memory these must have been about 10kHz and were clearly audible on half decent equipment. This would have been in the 70s and 80s.
In addition to manually forcing national network to mono when programme content so required, I seem to recall that in times past, some main VHF stations had Re-Broadcast Standby (RBS) arrangements that relied on the use of a 23kHz pilot tone being radiated in place of 19kHz to inhibit a link (or line) fed 'parent' station from trying to use a 'dependent' (Re-Broadcast Link-fed) station as its reserve feed in the event of the parent's own incoming feed failing - this would result in a howl-round scenario. Oxford and Wrotham come to mind ... Any ex-Beeb folks on here that have access to an archive copy of Network Routeings?
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Old 22nd Sep 2018, 12:45 pm   #29
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Default Re: FM stereo

I'm not referring to the actual 19kHz stereo pilot tone, these were easily audible tones of significantly lower frequency. I can't remember if they were used by the BBC or ILR stations (or both) though.
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Old 22nd Sep 2018, 7:11 pm   #30
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Default Re: FM stereo

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I seem to remember the Beeb used to make a point of turning the tone on and off depending on the source material, at least in the early years?
Quite so - in John Crabbe's review of the add-on decoder for the Quad FM1, he describes using the pilot-tone activated muting function to enable him to get on with work until the stereo programme started. This would have been late 1966, I think.
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Old 22nd Sep 2018, 7:36 pm   #31
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Default Re: FM stereo

I remember one Kenny Everett on Capital Radio flashing it just for fun - it might even have sent some morse but I forget.

Stereo lamp was implemented with a 12V 60mA SES bulb an a Ferguson Music Centre and at the time it was damn hard to
find replacements I do recall.

LEDS only appeared later.
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Old 23rd Sep 2018, 4:25 pm   #32
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Default Re: FM stereo

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The PLL-based decoder also had the advantage that it made things relatively easy to implement that all-important feature: a light that comes on when receiving a Stereo signal!
Cor, that makes me think of a Bush/Arena music centre (probably mid 70's) that used an entirely discrete decoder which (I think) used a pot-core transformer to step-up the 19 KHz pilot tone to a voltage sufficient to strike a wee neon! I hope I didn't dream this....
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Old 23rd Sep 2018, 4:40 pm   #33
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No, you were not dreaming, it was the Rank Arena RTA2000.

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Old 23rd Sep 2018, 5:32 pm   #34
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Default Re: FM stereo

Further to post #28, I made enquiries of an ex- BBC colleague (Keith Hayler) who has kindly agreed to my quoting him as follows:

"Hello Guy,

Ok, working from memory . . so no guarantee of absolute correctness:

VHF transmissions always have either a 19kHz or 23kHz tone present. 19kHz is derived from the 38kHz DSSC modulation of the L-R stereo 'difference' signal on a stereo transmission, enabling demodulation of the difference signal. On a mono transmission this is substituted by a 23kHz tone for 'validation' purposes, indicating the presence of a modulated signal, even in the absence of detectable baseband audio signal. I seem to remember that a pulsed 23kHz tone signals 'RBS inhibit' i.e. the station is using its RBS (mono by default) and hence may not be suitable as a reserve feed itself; the Wrotham/Oxford/Sutton howl-round scenario.

- on PCM/NICAM fed stations the transmissions can be forced to mono using the transmitter control channel, although I don't think I've ever known it to be used that way (user preference being that the 'red light' indicates a valid transmission). As you say, this would improve S/N in marginal reception conditions.

- on a line-fed station a combination of line tones is used to provide line validation and on/off stereo/mono control of the transmission (one tone = stereo, the other = mono, both present turns the transmitter off. Depending on line bandwidth these are either 10.6/10.8kHz or 14.6/14.8kHz. A notable instance of this system was for 'national regional' opt-out at Wenvoe, Divis and Shotts prior to the introduction of NICAM inserters."

I hope this is of interest.

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Old 23rd Sep 2018, 8:44 pm   #35
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Default Re: FM stereo

So you could theoretically implement a mono indicator as well as a stereo one if you were so inclined, provided you had sufficient IF bandwidth.
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Old 23rd Sep 2018, 11:34 pm   #36
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Default Re: FM stereo

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We certainly did that on R3 as mono gave a better signal to noise ratio in fringe areas.
I certainly remember that.

The 4.43MHz burst was turned off during monochrome TV programmes too.
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Old 24th Sep 2018, 8:12 pm   #37
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Default Re: FM stereo

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No, you were not dreaming, it was the Rank Arena RTA2000.
Thanks Ron.
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Old 25th Sep 2018, 1:36 am   #38
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Default Re: FM stereo

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Cor, that makes me think of a Bush/Arena music centre (probably mid 70's) that used an entirely discrete decoder which (I think) used a pot-core transformer to step-up the 19 KHz pilot tone to a voltage sufficient to strike a wee neon! I hope I didn't dream this....
I had a stereo decoder PCB with a neon beacon, I got it from one of the usual mail order suspects. Sounds like it was RBM surplus stock.

I think I put it in a Rigonda radiogram.
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Old 26th Sep 2018, 9:58 am   #39
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Default Re: FM stereo

That was the 'buzz' word at the time, 'beacon'.
All other indicator lights were just 'lights', but the Stereo indicator was a 'Beacon'.
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Old 26th Sep 2018, 11:40 am   #40
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Default Re: FM stereo

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Talking about stereo radio, does anyone remember the experimental VHF and MW Third program stereo tests, one channel from each radio?
Wasn't there also an experiment where one channel was on VHF radio and the other on Television sound? Last night of the Proms possibly.
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