Talk:405-line television system

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Half line

In the early days of 405, a line 1.5 lines long was inserted at the bottom of the frame. I forget the details of why, but something to do with synchronisation. This odd sized line was dropped fairly early in 405's history. Tabby (talk) 11:24, 26 November 2007 (UTC)[reply]

Almost. Aech odd field ended with half a line. The next field (an even field) commenced with half a line. Thus the two half frames of 202.5 lines combined to give a full 405 line frame. —Preceding unsigned comment added by 20.133.0.13 (talk) 12:50, 25 November 2009 (UTC)[reply]

This quote
"The number of lines was odd because of 2:1 interlace"
seems very hard for a non-specialist to follow. A brief explanation for the reasons (easily locates odd/even field; and analog vertical scan causes the lines to be tilted, so the extra half lines nicely fill in the thin wedge-shaped gaps at top and bottom) might be helpful - or perhaps a reference to some other place where it's described.

84.92.117.3 (talk) 14:18, 11 April 2016 (UTC)Jonathan Bromley[reply]

Spot wobble

Interesting concept but surely if would have been a lot simpler to decreace the focus voltage slightly to produce a larger spot (and hence thicker lines) ? 80.229.222.48 (talk) 20:54, 15 March 2008 (UTC)[reply]

It would have been simpler, but it would have reduced the horizontal resolution. Spot wobble produced an oval dot which was higher than wide, in order to reduce the visibility of the line structure. --Harumphy (talk) 12:17, 12 May 2008 (UTC)[reply]

New Zealand?

Can anyone give a reference or further information on the New Zealand part of "was also used for some time in Ireland, Hong Kong and New Zealand" as this is the first time I've heard that New Zealand TV broadcasting was ever in anything except 625 line format, originally CCITT B&W, later PAL.Kiore (talk) 10:59, 12 May 2008 (UTC)[reply]

It wasn't; the NZ government briefly considered it, but came to their senses. I've removed this from the intro. ProhibitOnions ^(T) 11:24, 15 May 2008 (UTC)[reply]

Cessation of transmissions in the UK

I have a few questions about this which I think would be best answered by having someone knowledgeable incorporate the relevant information into the article.

When 405-line broadcasts were stopped in the UK, how many people were still using equipment that could receive them?

Before the BBC or ITV decided to discontinue 405 from any given transmitter, they overlayed the 405 signal for months previously with a message saying "If you are reading this, please phone XXX". Allegedly at some Scottish main station, they got only 60 or so people call in to enquire in total. Of those, only about 3 were deemed to have be likely to actually lose service when 405 stopped. I used to have a reference for this anecdote, but have lost it. This sort of research accelerated the plan to discontinue 405. Originally the switchoff had been planned to complete in 1986. Steve Hosgood (talk) 12:13, 7 December 2012 (UTC)[reply]

Perhaps a better question would be, how many people were still watching when the decision was made to finally cease transmission? And indeed, when was this decision made? Presumably feasibility studies were conducted to determine how many people would be inconvenienced by it, so there will be figures in print somewhere.

The final decision was taken on 20 May 1980 by the Home Secretary. See here. Steve Hosgood (talk) 12:13, 7 December 2012 (UTC)[reply]

When were 405-line televisions last manufactured and sold? i.e., how antiquated did you have to be to one of those who ended up with a blank screen in 1985.

This page claims (half way down): "[...] a 1966 HMV 2634 "Imp" [...] uses the Thorn 980 chassis, the last single-standard 405-line-only chassis." So it would appear that you could still buy a 405-only TV in 1966, and the closedown started in 1982 - 16 years later. Steve Hosgood (talk) 12:13, 7 December 2012 (UTC)[reply]

Given that 405-line had better geographic coverage, were some people in remote areas left without reception after the switch-off, or was there a building programme in the 1970s and 80s to provide new transmitters so that the 625-line coverage problem was resolved in advance? If so, which transmitters are a legacy of this project?

There was a massive UHF relay building-programme in place during the 1970s and 1980s. As for legacy transmitters, look at 405-line transmitters of the United Kingdom. Most are still in use, having been reused for 625-line UHF initially and now reused as DVB-T transmitter sites. In places where the BBC and ITV masts were in close proximity, one would be chosen as the UHF station, the other typically became a telcomms site only, or became the VHF radio transmitter, and in some cases hosted the C5 service when it came out in the late 1990s. Some carry the DAB radio transmitters these days too. Steve Hosgood (talk) 12:13, 7 December 2012 (UTC)[reply]

Finally, what specific frequencies were used to transmit 405-line television? Was there any particular reason, technical or otherwise, for having them on VHF and 625-line on UHF? The article says they were sold off for DAB and trunked PMR, so there must be a specific band or bands with known bounds. Presumably people are listening to DAB right now on the same frequencies that they once watched 405-line television on!

Look at 405-line transmitters of the United Kingdom - there's a channels/frequency list on there. 405-line was on VHF Band I originally because in 1936 that was the cutting edge, and the only place you could expect to transmit a 7MHz wide (DSB) signal. By the time the ITV service began, the BBC had used up all five of the channels in Band I, but by then (the mid 1950s), technology had improved enough to make Band III a reality, and so the ITV channels went there. Post 1985 neither band has been re-used for TV, and you're right, listeners to DAB radio are listening to some of the same frequencies in Band III that the old ITV 405-line TV stations used! VHF wasn't reused for TV partly because when 625-line TV started in the UK it had to be on the UHF bands only. So in 1985 there were no VHF/UHF switchable TVs for 625 lines, and with VHF's rotten reputation for being affected by the weather, it was abandoned for TV. We didn't need it anyway - there was plenty of space on UHF. Steve Hosgood (talk) 12:13, 7 December 2012 (UTC)[reply]

Thanks. Beorhtwulf (talk) 20:50, 23 August 2011 (UTC)[reply]

Re first point, when I worked at the BBC (Publications) in 1985, I was told by an engineer that the Hull area VHF405 xmitter had developed a fault in the previous year, and ceased to broadcast, and it was only discovered three months later when a single user (a elderly lady) complained. This accelerated the decision at BH to switch off VHF. Maybe someone at BH Eng can expand. Interesting to contrast the main analogue switchoff recently, where a formal campaign was used. — Preceding unsigned comment added by 217.155.193.120 (talk) 23:08, 2 November 2011 (UTC)[reply]

Wrong!

"The 405-line monochrome analogue television broadcasting system was the first fully electronic television system" ?

The first fully electronic television system was shown by Manfred von Ardenne at the Funkausstellung Berlin, 1931: [1]

Heinzelmann (talk) 14:48, 25 October 2012 (UTC)[reply]

It might have been 'shown' but it was not used for broadcasting, so the claim is correct. 86.169.32.208 (talk) 18:12, 30 October 2013 (UTC)[reply]

The BBC had two systems running from 1936; the 405-line Marconi and the 240-line Baird, each at 25fps. The Baird xmitter was switched off 13-feb-1937.203.221.157.17 (talk) 02:38, 10 August 2016 (UTC)[reply]

Not the transmitter. The two systems shared the same transmitter. To say that the Baird system it was 'switched off' is not quite accurate. The Baird studios were destroyed by a fire three months into the six month dual system trial, prematurely ending it. --Elektrik Fanne 12:54, 12 November 2016 (UTC)[reply]

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