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Wrong UK 625 line TV system?

Pre War 240/405, Post War 405 Line, B&W Dual Standard, Colour Dual Standard, B&W S/S 625, Colour S/S 625 line, Hybrids. Standards converters & modulators, video recorders.
 
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Re: Wrong UK 625 line TV system?

Post by Synchrodyne » Sat Aug 08, 2015 3:51 am

Here is the IF bandpass curve for the 1961 Pye dual-standardreceiver. I had already attached this in the TV IF thread, but it is easier to repost here than to redirect.

WW 196110 p.514 Pye Dual-Standard TV.jpg


Cheers,

Steve

 
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Re: Wrong UK 625 line TV system?

Post by colly0410 » Wed Sep 23, 2015 10:55 pm

I'm thinking of some of the advantages of band 1: I think it would be cheaper to transmit for a given area coverage; so many watts ERP (or fractions of a watt ERP) per square mile covered, they would bend round hills better, less relay/gap filler stations needed & if the TX's are put on high ground with a tall mast the signal will go far. Think how far Holme Moss went on channel 2, it was coast to coast, I suppose it would have gone a bit further if it had used channel 1.... Then the disadvantages: Ignition/electrical interference, co-channel interference when sporadic E, F2, TE skip & tropo kicks in, large receiving aerials catching the wind & people saying they're ugly. (I think they're aesthetically pleasing but I'm biased. :) ) Anyone think of any other advantages/disadvantages of band 1?

 
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Re: Wrong UK 625 line TV system?

Post by ntscuser » Wed Sep 23, 2015 11:19 pm

colly0410 wrote:Anyone think of any other advantages/disadvantages of band 1?


It would only be able to carry a single digital multiplex which - in this multi-channel obsessed age - wouldn't be acceptable to many viewers even though that still represents more channels than many of had to choose from for most of our lives.

 
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Re: Wrong UK 625 line TV system?

Post by Synchrodyne » Thu Sep 24, 2015 7:10 am

The paucity of Band I channels was a drawback.

Use of the Band I channels for the main transmitters of a network, with Band III channels for the intermediate and gap-filling transmitters probably allowed the maximizing of Band I benefits.

But where Band I channels were also used for the intermediate and gap-filling transmitters, then the problems became apparent. Mutual interference problems limited the coverage of the additional transmitters, in turn requiring more of them, in turn exacerbating the channel-sharing problems, and so on.

One might say that the greatest strength of Band I – its long reach - was also its greatest weakness.

Cheers,

Steve

 
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Re: Wrong UK 625 line TV system?

Post by colly0410 » Thu Oct 29, 2015 4:54 pm

Been reading a book written by by a lady who lived in Port Stanley in the Falkland islands during the Argentine invasion. She says they started a TV service & rented out sets at next to no charge, she made one payment & that was that, they carried on TX'ing till they surrendered, they never asked for the sets back. The TV had a rabbit ears set top aerial & got a good picture. I presume they used standard system N Argentine spec TX's & sets & used band 1 to get maximum coverage for least power. I wonder what happened to the TV's? I understand they use system I at UHF now (unless they've gone digital) & relay British Forces TV..

 
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Re: Wrong UK 625 line TV system?

Post by Synchrodyne » Sat Oct 31, 2015 11:07 pm

I imagine that System N was used. It seems highly unlikely that the Argentineans would have done other than use their established system. As I recall, they changed the rule-of-the-road during their occupation, so that things would be done as they were on the mainland.

Given the distances from anywhere else with TV broadcasting, there was probably a free choice of channels. Band III would have required higher radiated power than Band I, but then aerial gain was relatively easy to obtain at these frequencies.

I’d pick channels A4, A5 and A6 as having been the best option. The very low end of Band I seems to suffer from problems that can cause significant frequency response lumpiness, particularly when relatively simple aerials are used. I saw an extreme case of this – really serious suckout at the sound carrier – with channel Aus2 in Sydney. But I have also seen it with channel NZ1 in Wellington and to a lesser extent with NZ2 in Auckland. In Dallas I had a multi-element array in the roofspace, but channel A2 was never as “clean” as channels A4 and A5, even though there was no shortage of signal. (The transmitters were more-or-less co-sited on an antenna farm over at Cedar Hill.)

Who knows, there might be a few System N TVs lurking in the UK, brought back by folk who spent time in the Falklands.

Cheers,

Steve

 
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Re: Wrong UK 625 line TV system?

Post by colly0410 » Fri Apr 22, 2016 2:13 pm

I wonder in any of the system N TV's left over in the Falklands by the Argentines were converted to system I? I presume they'd all have had a UHF tuner so all you'd need to do was move the sound gubbins up to 6Mhz, the colour subcarrier would have been a bit harder/impossible though so black & white only, pictures would be a bit softer than System I as well..

 
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Re: Wrong UK 625 line TV system?

Post by Terrykc » Tue Apr 26, 2016 8:02 pm

Synchrodyne wrote:... The very low end of Band I seems to suffer from problems that can cause significant frequency response lumpiness, particularly when relatively simple aerials are used. I saw an extreme case of this – really serious suckout at the sound carrier – with channel Aus2 in Sydney. But I have also seen it with channel NZ1 in Wellington and to a lesser extent with NZ2 in Auckland. In Dallas I had a multi-element array in the roofspace, but channel A2 was never as “clean” as channels A4 and A5, even though there was no shortage of signal. (The transmitters were more-or-less co-sited on an antenna farm over at Cedar Hill.) ...

I don't recall any problems like that with B1 from Crystal Palace except when I was at college.

We had a lab perched on the 4th floor of what was an essentially 3 storey building (2 extra rooms under the clock tower!) with good line of sight towards Crystal Palace/Croydon.

Croydon thundered in on B9 with just a short length of wire but B1 was very poor by comparison and really needed the external aerial connection.

Somebody worked out the reason one day. The windows on the wall facing the transmitters were narrow floor to ceiling metal frame affairs between the benches. The metal frames were behaving as exceptionally good absorption filters at B1 frequencies!

 
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Re: Wrong UK 625 line TV system?

Post by colly0410 » Sat May 14, 2016 6:51 pm

Wouldn't it have been fun (OK probably not) if the UK had adopted 525/50 as it replacement for 405? No one would ever export to us..

 
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Re: Wrong UK 625 line TV system?

Post by ntscuser » Sat May 14, 2016 6:55 pm

colly0410 wrote:Wouldn't it have been fun (OK probably not) if the UK had adopted 525/50 as it replacement for 405? No one would ever export to us.


Sony would have!

 
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Re: Wrong UK 625 line TV system?

Post by Synchrodyne » Wed Aug 03, 2016 4:51 am

Whilst I think it is clear that System N, or a derivative thereof is one of those compromises that would not be adopted except in extremely compelling circumstances, such as was the case in Argentina, something that made it even less likely in the UK case was an entrenched viewpoint that the vision bandwidth of any system should be sufficient to allow equal horizontal and vertical definition, and without any adjustment for assumed Kell factors.

That viewpoint seems to emanate from the late 1940s, when the UK decided to stay with its existing 405-line system whilst the rest of the world opted for higher line counts. The decision to stay with 405 lines was announced in Wireless World (WW) for 1948 October:

WW 194810 p.369 UK TV 405-Lines.gif


WW 1948 October included several features on the British 405-line TV system, including one entitled “The Fetish of Lines – Why the 405 Standard is Best”. A key point of this article was that the 405-line system allowed equal horizontal and vertical definition, and that made it better than any others extant or proposed. I have attached the first page:

WW 194812 S.5 405 Lines.gif


There were other similar articles, including one in WW 1949 March entitled “Television ‘Goodness factor’ – Why More Lines May Mean a Worse Picture”.

WW 194903 p.87.gif


In a narrow sense, all of that looks like a rearguard move to construct some technical justification for the UK decision, which was more in the nature of a distress status quo choice forced by its economic circumstances.

In a broader sense though it help to embed the notion of equality of horizontal and vertical definitions.

Still, the UK equipment industry was quick to see that the 405-line standard was definitely not an exportable item, as shown in these WW excerpts, which refer to a 625-line “export” system.

WW 194903 p.81  UK Export 625 Lines.gif
WW 194905 p.181 Marconi 625-Line.gif


Of note is that the proposed 625-line export system followed the Russian precedent with 6 MHz vision bandwidth and 6.5 MHz intercarrier, although FM sound deviation, at ±25 kHz, followed the 1945 American precedent. One imagines that Marconi WT would have thought this through and would have agreed with the choice of these parameters as being “right” for 625 lines.

Moving forward to 1956 August, this WW item again brings up the issue of the equality of vertical and horizontal definitions.

WW 195608 p.367 UK 625-Line TV.gif
WW 195608 p.368 UK 625-Line TV.gif


One conclusion was that for a 5 MHz vision bandwidth, around 500 lines would have been right, whilst for 625 lines, a 7.4 MHz vision bandwidth was required! That I think was a pie-in-the-sky goal, extrapolated from the 405-line case.

In comparing 625 and 405 line systems, it was said: “This improvement of 53% in vertical definition is accompanied by a proportional reduction in the visibility of the line structure, which is in itself a good thing. Too much importance should not be attached to it, however, for methods exist (e.g. spot wobble) by which the visibility of the line structure can be reduced.”

Clearly much less weighting was applied to the line visibility issue than had been the case overseas, and what was being said was more-or-less that line visibility was a problem, but that it could be masked.

It may be noted that NTSC 1st was stuck with the 6 MHz channel and the resultant 4 MHz vision bandwidth, but had a free choice of the line count. The “finalists” as it were in this competition were 441 and 525 lines, with 441 lines an early favourite. But eventually 525 lines was chosen because it significantly reduced line visibility and improved the flatness-of-field as compared with 441 lines, even though it incurred a reduction in horizontal definition. It was as if there were a line-count threshold, staying above which was more important than equalizing vertical and horizontal definitions.

One might say that the American viewpoint – followed in Europe and elsewhere – was that the line visibility issue was best solved by having a sufficient number of lines in the first place, whereas the British viewpoint, conditioned by familiarity with a system that had a below-the-threshold line count, was that masking was good enough. (Although I am not sure that spot-wobble was ever really developed to the point of being an everyday technique for domestic receivers.)

That 7.4 MHz bandwidth number for 625 lines was already in-play, as shown in this page from “Radio and Television Engineers’ Reference Book”, 1st Edition, 1954:

R&TVERB 1st p.10-4.gif


It was repeated in the 3rd Edition, 1960 (and I should imagine also in the 2nd Edition). So there was evidently a body of opinion in the UK that supported it, at least sufficient to justify its inclusion in a handbook that had some normative status.

The next stop is the 1960 TAC Report, of which a summary was provided in WW 1960 July:

WW 196007 p.322 TAC Report.gif
WW 196007 p.323 TAC Report.gif


The TAC technical sub-committee found that 625 lines with 5 MHz vision bandwidth was not quite good enough, and was thinking in terms of 6 MHz as being the “right” number. But after further deliberations and consultations, it came up with 5.5 MHz, along with a wider vestigial sideband, 1.25 rather than 0.75 MHz. Whether 7.4 MHz entered the picture at all is unknown. And the TAC’s thinking may have been constrained by the putative European 8 MHz UHF channel.

I think it would have been a brave soul who proposed a System N-like 625-line system for UK use in that climate, where the established viewpoint had been for a 7.4 MHz number and where even the TAC proposal might not have sat easily with that establishment. Also, there was probably at least a tacit view amongst the Europeans that the CCIR system was a bit more constrained, bandwidth-wise than it should have been. Those who were “locked-in” to it necessarily also used it for UHF, but those who were not chose a wider bandwidth system for UHF.


Cheers,

 
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Re: Wrong UK 625 line TV system?

Post by Synchrodyne » Wed Aug 03, 2016 4:53 am

Synchrodyne wrote:Also, somewhere along the way, the NTSC nominal vision bandwidth moved up to 4.2 MHz from the 4 MHz noted in the original NTSC I documents. This seems to have happened before NTSC II determined the colour system parameters. But on the other hand, the tabulation in Wireless World 1952 August still shows 4 MHz. By deduction, it looks as if System N started with 4 MHz and moved up to 4.2 MHz to stay in step with NTSC.


No, the change from 4.0 to 4.2 MHz bandwidth did come with the advent of NTSC colour.

This is well-recorded in the book “Color Television Standards – Selected Papers and Records of the National television System Committee”; Donald G. Fink, Editor; McGraw-Hill, 1955; LCC55-5684, see page 47.

The extension to 4.2 MHz was required to accommodate the colour subcarrier sidebands. It then appears that the FCC, in its rule amendment of 1953 December 17, specified 4.2 MHz as the nominal bandwidth for both monochrome and colour transmissions, see page 505 of the same book.

How that affected System N history is unknown. Probably it started at 4 MHz and then moved to 4.2 MHz, simply following the System M pattern. But on the other hand there is the previously recorded evidence – from 1950 - that the CCIR Gerber sub-committee was deciding between vision bandwidths of 4.25 and 5 MHz.

Synchrodyne wrote:Some of the “fine detail” remains obscure, though. For example, when was the NTSC TV standard, as developed by NTSC I in 1941, adjusted in terms of its sound carrier characteristics. Originally it was specified with ±75 kHz deviation and 100 µs pre-emphasis, the same as then used for FM broadcasting. Then it was later changed to ±25 kHz deviation and 75 µs pre-emphasis. My working hypothesis is that the two parameter changes were concurrent, and became effective with the 1946 channel assignments, but I have no supporting data. In the case of FM broadcasting, there is empirical evidence that 100 µs pre-emphasis was retained for the 42 to 50 MHz band at least up until 1945, and perhaps until the end of transmissions in this band. Again the (unsupported) working hypothesis is that 75 µs was prescribed for the 88 to 108 MHz band from the start.


The change to ±25 kHz maximum deviation and 75 µs pre-emphasis came with the 1945 December 19 issue of the FCC “Standards of Good Engineering Practice Concerning Television Broadcast Stations”. This followed the 1945 TV channel assignments and apparently superseded the original edition dated 1941 April 30, which showed the original ±75 kHz deviation and 100 µs pre-emphasis.

According to Fink, at the conclusion of WWII, the FCC had the Radio Technical Planning Board review the monochrome TV standards; they were reaffirmed in all essential particulars. I suspect that the change in the FM sound parameters may have come out of this review as a minor change.

Anyway, ±25 kHz maximum deviation and 75 µs pre-emphasis were well-established for System M by the time System N arrived.

In the FM case, ±75 kHz maximum deviation and 75 µs pre-emphasis for the 88-108 MHz band were delineated in the FCC “FM Standards of Good Engineering Practice” dated 1945 September 20, which was issued to cover the new band.


Cheers,

Steve

 
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Re: Wrong UK 625 line TV system?

Post by colly0410 » Wed Aug 03, 2016 3:20 pm

I'm wondering why spot wobble or some other line elongating methods were not used very often on large screen sets on 405. My Uncle Fred had a 23 inches 405 TV & you could clearly see the lines, biggest we had was 91 inches & you could just see the lines..

 
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Re: Wrong UK 625 line TV system?

Post by Till Eulenspiegel » Wed Aug 03, 2016 3:51 pm

The first dual standard sets made by STC were the KB VV series and certain models employed a refinement in which the spot was elongated vertically by supplying a 500volt negative voltage to the focus electrode of the CRT.
Line Eliminator Circuit. From the 1963/64 R & T servicing book, page 483:
This device is fitted to Models VV30, VV70 and VV80 to provide a means od softening the line structure, mainly on 405 lines. Rectification of the line flyback voltage provides a 500 volt potential which is applied to the picture tube focus electrode.

Till Eulenspiegel.

 
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Re: Wrong UK 625 line TV system?

Post by Till Eulenspiegel » Thu Aug 04, 2016 9:38 am

KB VV80 line eliminator circuit.

Till Eulenspiegel.
Attachments
VV70.jpg

 
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Re: Wrong UK 625 line TV system?

Post by nuvistor » Thu Aug 04, 2016 11:37 am

I never saw the KB circuit but the spot wobble I thought was not that good, only saw it in Ekco TV's though. Was the KB circuit a worthwhile improvment or did it look like a CRT with astigmatism.

Frank

 
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Re: Wrong UK 625 line TV system?

Post by colly0410 » Thu Aug 04, 2016 11:39 am

Thanks for info Till... Did any large screen 525 line sets use line elimination gubbins?

 
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Re: Wrong UK 625 line TV system?

Post by Till Eulenspiegel » Thu Aug 04, 2016 11:56 am

525 lines? Having that extra 120 lines and a 60Hz field rate perhaps there was never a pressing need for spot wobble or any other method of line elimination.
Yesterday I tried out the 23" Pye V600. I've got to admit this set needs some kind of device to close up the lines. Perhaps the KB circuit would work in the set. The circuit is said to elongate the spot in the vertical direction so closing up the lines.

Till Eulenspiegel.

 
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Re: Wrong UK 625 line TV system?

Post by Synchrodyne » Sat Aug 06, 2016 6:42 am

I have never heard of spot wobble or other similar devices being used on 525-line CRT receivers in order to reduce lininess. It would appear that 525 lines were “just enough” for CRTs up to about 27-inch diagonal. I recall comparing 525 and 625 lines on a 25-inch multistandard monitor-receiver, and whilst 525 looked just a little coarser in a vertical sense, it did not look liny.

For the UK, lininess and the perceived need for spot-wobble seemed to have been an issue from quite early on, judging by this item in WW 1952 January:

WW 195201 p.38 TV  Lininess.gif


A more light-hearted treatment of the subject is provided in this item from WW 1960 October:

WW 196010 p.518.gif


I wonder though whether screen size preferences were a causal factor or a resultant. In many countries, the 21 inch (later in squared-up 23-inch form) screen size became dominant once it was available, but apparently not so in the UK. Was it that UK viewers preferred smaller screens, and so were less bothered by the lininess of 405-line pictures, or did they resist upsizing because the of the lininess? Also, was there some level of acceptance of lininess as being just a normal part of the TV experience, given that it had been like that from the start.


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Re: Wrong UK 625 line TV system?

Post by colly0410 » Sat Aug 06, 2016 10:55 am

Read somewhere that when optical (TV camera of one system pointing at a TV screen of a different system) standards converters were used they always had to use spot wobble when converting 405 to a higher line number system, otherwise the results were dire, makes sense even to my thick brain. I wonder what 405 converted to 819 looked like? Probably slightly worse that the Belgian system F 819 lines system with it's reduced bandwidth I should think..

 
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Re: Wrong UK 625 line TV system?

Post by nuvistor » Sat Aug 06, 2016 3:09 pm

I don't remember the lines being visible being the cause of smaller screens being dominant, probably the extra cost of rental/purchase. It could be that the rooms in the UK tended to be smaller than elsewhere but no information to confirm that.
I suppose in a larger room sitting 12-15 feet away from the TV the lines would be less of a problem.

Some viewers put up with such a poor picture that lines would be the last thing they noticed. I went to someone's house, and the CRT was obviously very low emmision, they were happy with it. I could understand if they owned the set and did not want to spend money on it but it was on rental. Not my problem or my rental so best say nothing.

Frank

 
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Re: Wrong UK 625 line TV system?

Post by Till Eulenspiegel » Sat Aug 06, 2016 8:40 pm

Getting back to the subject of filling the gaps between the lines, at the start of the fifties Ekco was aware of the problem in the larger screen sets and offered a spot wobble unit to solve the liney picture problem.
Instead of separate coils on the CRT neck to perform the spot wobble task would it be possible introduce the 15Mhz sinewave into the frame deflector coils?

Till Eulenspiegel.

 
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Re: Wrong UK 625 line TV system?

Post by Katie Bush » Sat Aug 06, 2016 10:07 pm

On the other hand.....

I do recall once reading that visible lines were to some, something of a status symbol - odd, but feasible I guess, based on the notion that if you can see the lines, the set has far superior focus capabilities than lesser brands, and accordingly, in the eyes of many, better resolution.

From my own memories, when I owned a rather nice EKCO 21" 405 lines set (with 110 degree CRT) - can't recall the model but was around 1960 ish build, I would tweak up my focus for the sharpest possible line structure.. In truth, I don't recall the lines ever being an issue whilst viewing, even at fairly close quarters.

Like anything else, if you're immersed in your viewing, your eyes/brain make up for any shortfall - you're watching the show, not the "delivery system".. Many's the time I never even registered the fact I was watching in black & white!

 
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Re: Wrong UK 625 line TV system?

Post by ntscuser » Sat Aug 06, 2016 10:15 pm

Even sitting very close to a 19" set the only time I ever noticed the scan lines was when I turned my head sideways, which oddly enough I didn't do very often. I think the flicker became noticeable long before the scan lines did?
ttt:

 
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Re: Wrong UK 625 line TV system?

Post by nuvistor » Sun Aug 07, 2016 8:39 am

Katie Bush wrote:On the other hand.....
Like anything else, if you're immersed in your viewing, your eyes/brain make up for any shortfall - you're watching the show, not the "delivery system".. Many's the time I never even registered the fact I was watching in black & white!


This is very true, it's the content that matters, I wish broadcasters would understand that.

Frank

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