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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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20th Sep 2018, 9:30 am | #1 |
Nonode
Join Date: Jul 2010
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FM stereo
I was thinking about my first job, assembling 'radiograms' for Curry's circa 1967 and was trying to recall if the chassis' we were installing were able to receive stereo transmissions, I'm sure some of them did? But I then wondered if indeed FM stereo had even been introduced then - had it?
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20th Sep 2018, 10:16 am | #2 |
Dekatron
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Re: FM stereo
It took forever for stereo broadcasting to be rolled out.
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20th Sep 2018, 10:20 am | #3 |
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Re: FM stereo
I don't think there were any public stereo broadcasts in Britain in 1967. The BBC adopted stereo gradually from 1969 (?) onwards, and the first ILR stations launched in stereo in 1973. The first generation BBC local stations all launched in mono in 1967/8 and had to be expensively re-engineered for stereo around 1975, which was such a big job that many of them relocated to new premises.
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20th Sep 2018, 10:36 am | #4 |
Dekatron
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Re: FM stereo
VHF Stereo transmissions started on July 30 1966 from Wrotham in Kent with the Midlands and North of England to follow shortly after. I presume that would be Holme Moss and Sutton Coldfield.
Only the Third program was in stereo and only for 3 or 4 hours a day. Ref WW Sept 1966. Page 438 https://www.americanradiohistory.com...ld-1966-09.pdf We had some interest but it was in the 1970’s when more popular stations introduced Stereo that we started to sell sets with a decoder, by then the better products had the decoder built in. I understand that one problem for the BBC in extending the number of transmissions was the PO lines not being good enough. The BBC R&D used PCM, yes digital, to reach the further transmitters in the early 1970’s. I need to find a reference for this, unless someone can confirm. Found this although a BBC paper would be better. http://www.audiomisc.co.uk/BBC/PCMandNICAM/History.html
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20th Sep 2018, 10:41 am | #5 |
Nonode
Join Date: Jul 2010
Location: Folkestone, Kent, UK.
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Re: FM stereo
Thanks Paul, seems like a case of false memories on my part then
The chassis were mostly valve but one or two "top of the range" models were solid state and I have an image in my mind of them having a stereo indicator? But since we tested them in the most basic way by scratching the stylus and tuning through the LW/MW/FM the stereo bit cant have happened? Thanks Frank, that's interesting as the factory was in Catford south London, so not far from Wrotham so perhaps it was possible? |
20th Sep 2018, 10:48 am | #6 |
Dekatron
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Re: FM stereo
I think, could be wrong, but the public were more interested in colour television than stereo radio, especially if it was only Radio 3 as it was to become known in 1967.
Three channel CTV arrived in many areas before all BBC stereo radio in November 1969. Other thoughts appreciated, it’s a long time ago so my memory has faded. Talking about stereo radio, does anyone remember the experimental VHF and MW Third program stereo tests, one channel from each radio?
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20th Sep 2018, 11:46 am | #7 |
Dekatron
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Re: FM stereo
The timeline for stereo broadcasts is roughly this - the first two-transmitter experiments were in 1958 and continued, usually on Saturday mornings, until 1964. There were also experimental transmissions on the multiplex system from 1962. The EBU did not agree on the stereo transmission standard until 1966, when it adopted the system the BBC had been using.
Scheduled transmissions started on the Third Programme around the Proms season in 1966. The first announced stereo transmission (if the note in a tape box I have is to be believed) was a Midday Concert from Maida Vale 1. The two biggest problems with the general introduction of stereo broadcasts were the provision of stereo equipment in studios, which was largely a finance and logistics issue, and the distribution of stereo programme to transmitters. Experience with the two-transmitter experiments had indicated that PO lines weren't up to the task of providing sufficient bandwidth and phase matching over long distances, and the solution eventually adopted was the 13-bit PCM distribution network, which came on line in 1972. The launch of stereo on Radio 2 and Radio 4 was timed to coincide with the 50th anniversary celebrations later that year. I went to the Audio Fair that year and remember the excitement around the launch. By that time, the centre of gravity of the market had shifted to stereo separates over radiograms. Local Radio remained mono into the 1980s. A running joke during Sounds Good, Radio London's hi fi programme, was "when are we going stereo?" Poor John Longden, then EiC, got rather tired of fielding the flak, I think...of course, BBC local stations carried network as a sustaining service, so to provide decent stereo from their service required a PCM contribution circuit as well, which took time to install. ILR had fewer worries on this score, as networking, apart from news, wasn't part of the plan. (Post crossed with Nuvistor) |
20th Sep 2018, 12:04 pm | #8 |
Dekatron
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Re: FM stereo
I do remember the Radio Times having programmes endorsed 'Stereo' but can't remember the date - mid 1970's I would guess.
The BBC also transmitted, after closedown, test transmissions to help with decoder adjustment - pilot signal only; 1kHz (?) both channels; left channel only; right channel only; all repeated a few times. Presumably with 24/7 programmes on all stations, this has stopped? |
20th Sep 2018, 12:14 pm | #9 |
Hexode
Join Date: Oct 2016
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Re: FM stereo
Here's an interesting article on the roll-out of PCM and FM/VHF stereo in the BBC national networks
https://www.bbceng.info/Technical%20...digits-fm.html |
20th Sep 2018, 10:52 pm | #10 |
Dekatron
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Re: FM stereo
When you consider the number of decision-making boards around the world, it strikes me as surprising and fortunate that the Zenith-GE system became so ubiquitous.
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20th Sep 2018, 11:07 pm | #11 |
Dekatron
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Re: FM stereo
The process was fairly tortuous, but once the US went for a pilot tone multiplex system, it was a fair bet (admittedly in retrospect) that the rest of the world would follow. Of the rivals, the Percival system was farcical in practice, and another system which had sufficient crosstalk immunity to allow twin language programming didn't gain traction in Europe as a whole, as the degradation of service area was too great. The BBC held back until the Zenith-GE system had been agreed, partly to enhance the export potential for UK manufacturers.
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21st Sep 2018, 3:13 am | #12 |
Nonode
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Re: FM stereo
I think it could be said that the FCC had done a good job when it decided upon the Zenith-GE system in 1961. Both the Zenith and GE proposals – which were separate submissions but combined by the FCC – were I think fairly late arrivals, prior to which there had been some expectation that the Crosby FM-FM system would be the winner. I think that the Crosby system supporters were somewhat upset, but given the weighting that was given to maintaining the mono service area and allowing room for an SCA carrier, it is difficult to see how there could have been any other outcome.
The Russians had opted for their own polar modulation system. I understand that this was seen as better suited to their ±50 kHz maximum deviation Band I broadcasts, although I am not sure I know why that was so. The outcome of the CCIR deliberations had been presaged by the BBC in 1965: And here are the pertinent documents from the CCIR 1966 Oslo meeting: CCIR 1966 Oslo Recommendation 450 Stereo.pdf CCIR 1966 Oslo Report 300-1 Stereo.pdf The Swedish FM-FM system mentioned in the CCIR Report was really a derivative of the Crosby system. The Japanese developed a similar system for TV stereo sound in the 1970s, and the Swedish system was later proposed for European TV stereo sound, although in that case the IRT and Nicam systems won the day. Cheers, |
21st Sep 2018, 5:02 pm | #13 | |
Nonode
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Re: FM stereo
Quote:
Alan |
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21st Sep 2018, 5:22 pm | #14 |
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Re: FM stereo
Yes, it's certainly not impossible, and I didn't mean to imply otherwise.
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21st Sep 2018, 5:51 pm | #15 |
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Re: FM stereo
Stereo decoders aren't rocket science, so one could be built out of whatever devices one prefers or has handy. A bucket full of 807s, a handful of EF80s or a handful of BC108s.
The choice comes down to the builder. There were relatively few valve designs, fewer in the UK than the US due to the relative timing of the adoption of stereo and the adoption of the transistor. Most, not all, of these designs were simplistic to keep the valve count down and were a bit crude. But then so is a crystal set and people still build them. The decision comes down to interest and a fun factor. Though I don't know of anyone who uses a crystal set as their daily listening set. A more capable stereo decoder could be designed around valves if someone wanted, but they'd have to do the design work, bash the chassis and wind the coils. One of the better valve designs from the US could be replicated, but it may be necessary to reverse engineer the design to arrive at the design of the wound inductors and then procure equivalent bits. It would be less design work, but design skills would be needed for the reverse engineering. The PLL-based decoder was seen by manufacturers as chiefly a way of avoiding coils. If you take the older tuned circuit frequency multiplier approach, whether you use transistors or valves you run into the need to find cores and wind coils. Coils can be made. It's a useful skill and opens up a lot of things to you if you learn. David
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21st Sep 2018, 8:04 pm | #16 |
Nonode
Join Date: Jul 2010
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Re: FM stereo
Thanks Alan for info regarding Pye 1207. Of course my memory of events 50 years ago cant be entirely trusted, although in my minds eye I can see the stereo indicator lighting? Is there anyone out there with a late 60's Curry's radiogram - not many I'll bet!
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21st Sep 2018, 8:19 pm | #17 |
Dekatron
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Re: FM stereo
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!
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21st Sep 2018, 10:16 pm | #18 |
Nonode
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Re: FM stereo
Insofar as the IC-type PLL decoders (CA3090, MC1310, etc.) incorporated stereo indicator drivers, then it was very easy for the equipment makers to provide stereo indicators. But the preceding non-PLL ICs (e.g. MC1304/5) also had the same facility. Discrete PLL-type decoders were I think rare in production. The Portus and Haywood design described in Wireless World 1970 September used the lock detector output to trigger the lamp driver, so that was very simple. With non-PLL discrete transistor designs, the arrangements would have varied. But where a full-wave rectifier was used to double the 19 kHz pilot tone, that might have provided a suitable DC output to trigger the indicator driver; not too complicated, but requiring an extra transistor or two, which might have upset the bean counters enough to outrule it in some cases. So in that context, the coil-less MC1310 and its ilk probably enabled the production of all-facilities stereo decoders at lower cost than bare-bones non-PLL discrete models, so that stereo beacons moved from being an optional deluxe item to standard equipment.
Cheers, |
21st Sep 2018, 10:54 pm | #19 |
Dekatron
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Re: FM stereo
According to the Science Museum booklet "Broadcasting in Britain 1922 - 1972" (published in 1972) , the stereo service was " ... extended to parts of the Midlands and the North of England in 1968; this gave a population coverage box about 60%, but little further progress has been made by 1972.
Extension of stereophony to the 'light music' network (scheduled for Autumn 1972) has been delayed by the need to provide stereo facilities in the numerous studios contributing to the network." My first stereo receiver was one I built from a design published in the Wireless World in the early 1970's. It worked OK, bit I never did make a proper case for it. Last edited by emeritus; 21st Sep 2018 at 11:11 pm. |
21st Sep 2018, 11:02 pm | #20 |
Dekatron
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Re: FM stereo
I built one around 1969 using (I think) a single ECC82
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