British use of high band.

[Robert Grant]

British monochrome analog television used only 405 scanning lines and only 25 frames per second, resulting in only 10,125 lines transmitted per second (compared with 15,750 or 15,734.2xx per second for USA analog television). This meant that the British system only needed 5MHz for a television channel instead of America's 6MHz, and yet had more horizontal resolution than American television

This allowed the UK to place eight highband channels 6 through 13 in Band III with two MHz left over.

Note that Britain's five Band I channels ended at 68MHz and that they never had Band II over-the-air television at all.

Unusual about UK television is that it has been through not one, but two, incompatible transitions.

From 1964 to 1985, they had the 405-line VHF to 625 line UHF transition, including television sets in the UK that were dual standard sets, which switched from positive modulation 405-line video with AM audio and -3.5 MHz audio offset, to negative modulation 625-line video with FM audio and +6MHz offset when the user switched from VHF (BBC1 and ITV) to UHF (BBC2).

From November 1969, UHF 625 line transmissions of BBC1 and ITV were added, so television sets made from about 1970 onward had no 405, positive picture detection, AM audio, nor VHF tuner.

The second transition was done like everywhere else in the world. UHF Digital transmitters were shoehorned among UHF analog transmitters with the latter shut down years later and some improvements made to the digital transmitters later.

[Colly0410]

Originally Posted by Robert Grant

From 1964 to 1985, they had the 405-line VHF to 625 line UHF transition, including television sets in the UK that were dual standard sets that switched from positive modulation with AM audio and -3.5 MHz audio offset with 405 lines to negative modulation with FM audio and +6MHz offset with 625 lines when the user switched from VHF (BBC1 and ITV) to UHF (BBC2).

From November 1969, UHF 625 line transmissions of BBC1 and ITV were added, so tellies from 1970 on, so tellies from 1970 onward had no 405, positive picture detection, AM audio, nor VHF tuner.

Some dual standard sets were still being used into the 1980's, they were so complicated though that they were scraped as they were too difficult to mend when they went wrong. I've got a 625 lines UHF only set from 1971 that still works when fed from a digital box UHF RF output.

The last 405 lines VHF only sets were sold in 1968/9, 5/6 years after 625 started, mind you the 405 lines VHF transmitters carried on broadcasting till the 1980's, the last ones shutting down on 31 Jan 1985, but almost everyone was then on 625 lines colour at UHF & no one noticed, there's a you tube video of it. Colour was never broadcast on 405 VHF. BBC2 fired up with colour in 1967 on 625 UHF, & BBC1 & ITV fired up in colour in November 1969, also on 625 UHF. All Antenna TV is now digital at UHF only..

[TV-collector]

Thanx for this interesting news report!

TV-collector

[Adlershof]

Originally Posted by Colly0410

ind you the 405 lines VHF transmitters carried on broadcasting till the 1980's, the last ones shutting down on 31 Jan 1985, but almost everyone was then on 625 lines colour at UHF & no one noticed, there's a you tube video of it.

Indeed: The person, with her face never appearing in vision, waves into the camera and then turns off the 405 lines set, so the actual shut-down was not captured anymore


The BFBS problem was well known in Berlin back then. How did this UK-only system with sound on +5.996 MHz (that's how literature defines it) arise, this oddball in between B/G and D/K?

These armed forces transmitters survived much beyond the eighties. In the case of AFN the last ones disappeared only a few years ago, when anything else was already gone. Closure of the last BFBS TV transmitters in Germany was in 2008.

What disappeared much earlier were of course the Russian and French transmitters. They carried SECAM video in B/G, so no hassle with D/K or even the completely incompatible L norm here.

[Colly0410]

Originally Posted by Adlershof

Indeed:

The BFBS problem was well known in Berlin back then. How did this UK-only system with sound on +5.996 MHz (that's how literature defines it) arise, this oddball in between B/G and D/K?

.

Read in a TV mag that the reason Englands 625 system I chose +5.996 (originally +6 MHz) was so they could extend the video bandwidth up to 5.5 MHz as they didn't think the B/G bandwidth of 5 MHz was enough, & they didn't choose the 6 MHz video bandwidth of D/K as they wanted a vestigial sideband of -1.25 MHz for some reason. (D/K uses 0.75 MHz) Of course there could be a bit of protectionism thrown in as well so people couldn't just import European system B/G TV sets into England & they'd work OK. So they made the system just a little bit different to mess things up for Mr & Mrs Public. Just my cynical 10 cents worth..