1946 Why 405 lines?

[peter_scott]

I know this topic has been discussed before but I was looking for the official enquiry/report leading to the decision and found an on-line copy of the Hankey Television Committee that was appointed as early as September 1943 to examine the question. I agree with the findings but I think it still makes interesting reading.

Peter

Below is the list of witnesses:

[Graham G3ZVT]

J Arthur gets double billing, whilst J Logie seems to be included as an also-ran.

[Hartley118]

There are some distinguished names on that list!

I recall a TV engineer (possibly from the ITA) expressing the view that, with the CRT sizes available, it was hard to beat the subjective crispness of a 405 line picture. Maybe it was the way that vertical and horizontal picture definitions were very similar given the video bandwidth available.

Martin

[Panrock]

Originally Posted by Hartley118

... it was hard to beat the subjective crispness of a 405 line picture.

So sharp, you can see the lines!

Steve

[peter_scott]

Originally Posted by rambo1152

J Arthur gets double billing, whilst J Logie seems to be included as an also-ran.

Well, after all it was cinema television that was all that was left to Baird after the fiasco of his company's performance in November and December of 1936.

Originally Posted by Hartley118

I recall a TV engineer (possibly from the ITA) expressing the view that, with the CRT sizes available, it was hard to beat the subjective crispness of a 405 line picture. Maybe it was the way that vertical and horizontal picture definitions were very similar given the video bandwidth available.

Martin

It's interesting that the principal advantage of the 625 line system over 405 is the 55% increase in vertical resolution giving a large reduction in picture "lininess" but using the 8MHz channel bandwidth only gives a 20% increase in horizontal resolution over 405 line sets with 2.5MHz bandwidth and no advantage if the 405 line sets have 3MHz bandwidth.

Peter

[Panrock]

In the document cited above, we read (of the vision-sound ratio):

The ratio chosen, viz., 17 kW peak vision and 3 kW sound, proved in practice to be a reasonably satisfactory combination, although in the opinion of some observers the sound transmission tended to lack power and hi consequence was marred by interference at shorter ranges than was the vision.

So the pre-war (and presumably the post-war AP vision-sound ratio) was 7½ dB. Does anyone know if and when it changed to 6dB, as used by the Aurora?

Steve

[G6Tanuki]

Having read a bit about this some decades ago, I suspect that there was quite a degree of pragmatism involved, of the "let's get the telly working again and show the population that Britain is getting back on its feet" kind.

Re-engineering to another line/frame standard [525 lines 25 frames/sec? Benefiting from the advance of US TV developments during WWII?] would have been an advance, but it would have obsoleted existing gear.

I see getting-a-TV-service-up-and-running-again-in-postwar-times as being a political goal in its own right, standards notwithstanding.

For the 'poverty-spec' TVs (often rented) with 17-inch-or-smaller screens which were the default in late-40s/early-to-mid-50s Britain, 405 lines was ~~good enough~; if I'd been part of the Television Committee my mind would have been much more focussed on rolling-out a second (and maybe a third) channel - both commercial - in parallel with the creep of the BBC to Sutton Coldfield, Wenvoe, North Hessary, Kirk O'Shotts, Holme Moss etc.

[G6Tanuki]

Originally Posted by Panrock

So sharp, you can see the lines!

Steve

Hence "spot-wobble". https://vintage-radio.net/forum/showthread.php?t=34521

[dave walsh]

Baird was about to present a new colour electronic system in London but became ill and died [here at Bexhill] in June 1946, before that could take place!
I think Tanuki's 405 line overview looks fairly accurate.

The politics around BBC trials of 405 v 625 line colour in 1966 are even more interesting. The technical conclusion was that 625 was superior but it's clear from the study published in Wireless World that, actually, the members of the public in the viewing audience couldn't really detect any difference. There have been threads on this as well.

Dave W

[Graham G3ZVT]

When I took some 35mm screenshots of the Apollo 11 landing I chose to take them off the BBC 405 line coverage. The 625 picture quality on the Bush dual-standard rental set we had seemed subjectively poorer.

[JohnBHanson]

Of course the number of lines was chosen to be a multiple of low prime numbers. For an interlaced system all these numbers must be odd as the total number of lines per frame has to be odd.

eg for 405 this is 3*3*3*3*5
for 625 lines this is 5*5*5*5
and 525 lines 3*7*5*5

[peter_scott]

Originally Posted by rambo1152

When I took some 35mm screenshots of the Apollo 11 landing I chose to take them off the BBC 405 line coverage. The 625 picture quality on the Bush dual-standard rental set we had seemed subjectively poorer.

Ah yes! 50 shades of gray. I remember that too.

Peter

[Ted Kendall]

The overriding reason for retaining the pre-war standard was economic - the USA cut off Lease-Lend shortly after the war ended, there were no resources to make domestic receivers to the existing standard, never mind a new one. It was bad enough recommisioning the scanners and studio kit in time for the Victory parade.

I recall a film clip in All Our Yesterdays in which one of the BBC high-ups of the postwar television service recalled the first problem on his desk being deciding the aspect ratio of future transmissions. He happily admitted he didn't have a clue what aspect ratio was...

[vidjoman]

Many of the early 625 sets and the adapted ones were rather grey. When we got to 625 only sets it improved and was also about the time of early colour which required a proper black level.

[Skywave]

I always thought that the number of horizontal scan lines and at the chosen field rate was dictated by the available bandwidth at 45 MHz (approx.), when BBC was the only transmission. When Band 3 became available - used by ITV - that scan rate (etc.) had become the standard, despite the fact that at Band 3, the bandwidth could be greater. With the arrival of Band 5, the availability of a much greater bandwidth enabled 625 lines to be achieved and thus that became the new standard.

If I am mistaken in any of the above, then please tell me!
Thanks.

Al.

[1100 man]

Originally Posted by Hartley118

I recall a TV engineer (possibly from the ITA) expressing the view that, with the CRT sizes available, it was hard to beat the subjective crispness of a 405 line picture. Maybe it was the way that vertical and horizontal picture definitions were very similar given the video bandwidth available.

I would have to agree with that! A good 405 line picture has a certain something about it and and can look very good.

From a purely 'entertainment value' point of view, it makes no difference to me if I am watching in 405 or 625 and I view material on both standards quite often. I doubt if most of the public were much bothered about the difference at the time. The main advantage of 625 is I can no longer hear the line whistle

Cheers
Nick

[peter_scott]

Originally Posted by 1100 man

The main advantage of 625 is I can no longer hear the line whistle
Cheers
Nick

Oh what! You mean that you don't have 10.125kHz tinnitus constantly playing in your head whilst watching 625?

Peter

[emeritus]

I seem to recall that when they started transmitting programmes in widescreen fomat with black bars at top and bottom on a 4:3 TV, the effecitve number of lines was close to 405.

[Catkins]

Originally Posted by peter_scott

Well, after all it was cinema television that was all that was left to Baird after the fiasco of his company's performance in November and December of 1936.

I found it conspicuous that "J. L. Baird, Esq., F.R.S.E" is given without any company affiliation, whereas others are associated with a company or trade organisation, i.e. What happened to his "Baird Television Limited" which ran the 1936 television trails? Intrigued I did a bit of browsing.

On the basis this might be interesting for others, it turns out Baird Television Limited went into receivership in late 1939, and was later absorbed into Cinema-Television Ltd. Both of these were owned by the parent company Gaumont British Pictures (BTL being taken over by them in 1932).

It is mentioned that "it appears that Baird had no formal link with CinTel and received no salary from them".

So it would appear Baird worked privately through-out the war on cinema and colour television, and in 1946 set up "John Logie Baird Limited", which produced a number of high end televisions.

Scophony Ltd which is mentioned in the organisations present merged with John Logie Baird Ltd in 1948, to produce Scophony Baird Ltd, which went onto produce a range of "Baird" televisions in the late 40s/50s.

Scophony was mostly associated with cinema television in the 1930s, and there does seem to be a heavy emphasis on cinema in the organisations and witnesses present. There is no explicit mention of Cossor, Murphy, or Pye. But C. O. Stanley of Pye is there in the guise of the "Radio Industry Council". Does anyone know the affiliations of the other people mentioned?

Perhaps the emphasis on cinema is not too surprising given it is there where 405 line definition would be felt most problematic.

Originally Posted by peter_scott

It's interesting that the principal advantage of the 625 line system over 405 is the 55% increase in vertical resolution giving a large reduction in picture "lininess" but using the 8MHz channel bandwidth only gives a 20% increase in horizontal resolution over 405 line sets with 2.5MHz bandwidth and no advantage if the 405 line sets have 3MHz bandwidth.

Peter

I know most 1930s/40s televisions could not achieve 3MHz bandwidth. Did 1960s 405 televisions achieve the full 3MHz bandwidth? I imagine this would have been the case by then, except for cheap small CRT televisions?

[peter_scott]

Originally Posted by Catkins

I know most 1930s/40s televisions could not achieve 3MHz bandwidth. Did 1960s 405 televisions achieve the full 3MHz bandwidth?

Well all the first generation EMI sets were capable of full 3MHz bandwidth

Peter