Weak 405 transmitter power at the end

[Panrock]

I have mentioned elsewhere that I was able to receive a good picture on my pre-war receiver from Crystal Palace on one occasion in winter time, when there was a continuous path of fog between London and Sedgeberrow. The distance is approximately 100 miles.

Nevertheless, this occurred very near the end of the Channel 1 service in January 1985.

I understand that at this time Crystal Palace (and the other BBC 405-line main transmitters) were radiating at far below their declared power. In the case of CP I seem to remember the declared pk-white erp was 200Kw.

Two questions:

1) Did this nefarious practice also extend to the ITA transmitters?

2) What was the actual estimated e.r.p from Crystal Palace Ch1 in her final days? Was it even less than that previously coming from AP (namely 17 or 34 Kw)? Would it in fact have then just been an S.T & C CG1 keeping up the appearances - meaning less than 1Kw ??

Such is the experience on tap here, somebody must know ....

Thanks,

Steve

[Paul Stenning]

Did you read "Fables from a Cold Field" in the BVWS bulletins last year?

Sutton Coldfield were putting out just a few hundred watts towards the end - something like one hundredth of the original power, and nobody noticed. Even the Hereford relay kept working OK with that!

I don't know whether that included IBA though - I think Sutton Coldfield may have been just BBC.

It doesn't really answer your questions, but it is background info on what went on...

[thyratron]

Steve
I was able to receive Xtal Palace on Odd Down in Bath (approx 100 miles) at a height of 700' above sea level during the last year of BBC 405 lines.
I had a 'modern' dual standard Baird 640 at the time and a home made wide spaced 'H' aerial on a 12' mast.
The signal was about 50 uV most of the time and was watchable ish!! so long as local interferance was quiet.
When a plane went over,within about 3 miles the picture would come up out of the noise and die back over and over ....remember that!!!
The Chan 4 signal from Birmingham was over 100 uV when the Chan1 aerial was swung around!(should have been stronger) and the Wenvoe aerial would yeild about a millivolt.
I remember the frustration with all this was that for over a year before switch off, the Wenvoe signal was strong but there was a terrible problem with black level clamping giving awful pictures. DID ANYONE ELSE NOTICE THIS
I wrote and complained to the BBC who admitted the problem but said they could not get the parts. (was there a problem with the standards convertor??)
HOWEVER
the London and Birmingham signals were weak but properly modulated and that was the choice...snow storms & fading or disappointing murky Wenvoe!
I reckon there was major troubles at Wenvoe and Birmingham but London seemed good from here!
I may have some photos of all this somwhere!
THYRATRON

[Focus Diode]

I moved three times during the last three years of 405-line tv. In 1983 North Hessary Tor ch2 (in Torquay) still gave superb pictures although Stockland Hill ch9 was weak. In 1984 on returning to the North East ch5 Pontop Pike continued to give excellent results although Burnhope ch8 was suffering from vertical lines which seemed to crawl up the screen like worms.

Pontop Pike ch5 continued after Burnhope ch8 closed down, although very weakly received, it seemed to fade out to nothing during the afternoon of early January 1985. Burnhope's closedown was even mentioned by TTT announcer Neville Wandless during a "Lookaround" feature, mentioning, "The loss of our old friend who was getting rather old".

In 1984 I was able to receive Yorkshire tv Emley Moor ch10 during a tropospheric lift.

Sigh of nostalga- I still often dream of receiving 405-line transmissions!

Brian R

[Hybrid tellies]

I use to live near to Thyratron (just down the road in Dunkerton), despite being down in a dip, with a wire aerial and a RBM A640 dual standard set I could pick up the weak Wenvoe transmission on ch5, it had terrible sync problems.
I could also just about receive the North Hessary Tor transmission on ch2 and Rowridge on ch3. This was in 1983/84. I can certainly vouch for the low powered and poor quality Wenvoe transmission.
Ref the IBA, I think it was in the 1970's that the St Hilary ch10 200Kw transmitter went up in flames. When it came back on air it was only 55Kw's.
I did hear that by the late 1970's both the BBC and IBA were struggling to keep the old 405 line network going. The main problem was lack of parts their engineers were rumoured to be searching all the old second hand electronic shops across many parts of the country. This is the reason that they ran most of the 405 transmitters on reduced power to preserve the life of the final PA stages.

[ppppenguin]

A lot of poor 405 pictures in the later days may have been due to converter faults rather than actual transmitter problems.

The BBC designed the CO6/509 digital 625>405 converter in the early 1970s because they reckoned that 405 would last longer than the useful service life of the CO6/501 and CO6/501A analogue converters. They were right! The CO6/509 was a very good design that could run stably reliably for long periods without attention. It may be the first item of digital video equipment that was regularly used on active service anywhere in the world.

ITV struggled on with Pye built versions of the CO6/501 and CO6/501A. They must have been a nightmare to maintain in the later days.

[Heatercathodeshort]

The BBC transmission from CP appeared to retain its very high quality to the very end. I was only a few miles from the transmitter, but the sensitivity control on my HMV 900 was never moved from its near minimum position over many years [and no AVC!]
The ITA transmissions [?] were nothing short of terrible with a massive hum bar, low contrast and very low sound. I did phone the IBA and they told me that both standards converters were just about dead and I had the choice of the one with the hum bar, or the other with no sync! On the last day the vision failed completely and I have a tape recorded over the last few days to prove it! The final words were 'Beulah Hill is now closing down' in sound only.
Regards John.

[ppppenguin]

Originally Posted by Heatercathodeshort

.... The ITA transmissions [?] were nothing short of terrible with a massive hum bar, low contrast and very low sound. I did phone the IBA and they told me that both standards converters were just about dead and I had the choice of the one with the hum bar or the other with no sync! .....

John, thanks for providing the evidence to back up my conjecture about the analogue converters. I missed the 1985 shutdown because I only got interested in vintage TV in late 1985. I don't think I even had a 405 capable set at the time.

[Hybrid tellies]

I missed the final shutdown as we were involved in a big move at the time.
Going back to power reductions, when I first moved to dear old Dunkerton (Nr Bath) back in 1976, I could watch BBC1 on ch5 from Wenvoe using an old GEC dual standard set with a suitable length of wire as an aerial, the pictures were good but as soon as any daytime programmes came to an end and they returned to the testcard the power was swiftly turned down.
Which just goes to show that they were struggling to maintain some of these old transmitters many years before the final shutdown.

[Paul Stenning]

These posts about the state of the equipment certainly show why the decision was made to close the service. There must have been very few viewers in the last few years, and it obviously was not viable to keep this system going any longer.

[Ian - G4JQT]

I knew an engineer who worked occasionally at the 405-line transmitter serving Carlisle and surrounding areas. He said that at some time in the early-mid 1980s the tx had to run for a while on reduced power, expecting most viewers to be watching on UHF by now and that no one would notice.

But they very soon got to hear of many complaints about poor picture quality. They were rather worried that in the next year or so when it was to be closed down, all hell would break loose! Presumably either many of the the isolated communities were not able to get a good UHF signal and/or many of the locals just couldn't afford new sets.

He said it would have been much cheaper to drive round the area and deliver new sets to those on VHF rather than struggle to maintain the station's equipment.

My suggestion to him was to gradually reduce the power (if possible) over some months until people decided that their sets are failing and buy new ones! It seems that to prolong the life of the transmitters this was done sometimes anyway...

Ian

[Ray Cooper]

Speaking as an insider, I can say that it was a pretty close-run thing that most of the sites made it to 1985. By this date, the age of a lot of the larger broadcast equipment was in excess of thirty years. The Beeb always used to have a target of 25 years for replacement of its capital plant, so most of the gear would have been due for replacement by 1980 - and it was clearly not going to be an economic action to do that when the service was only going to last a few years more.

By 1980, spares for some of the older gear were getting very difficult to obtain (at least one species of valve was being hand-made in almost one-off quantities at this time - the BBC was the only outfit in the world still consuming them). Wiring of some of the older stuff was becoming a nightmare, too (Sutton Band I vision was almost entirely wired in rubber-covered cable - high temperatures, dripping transformer/capacitor oil, and thirty years, hadn't done much to maintain its pristine quality. Loud bangs and small fires were not uncommon).

Somebody mentioned the CO6/501 analogue standards converters. The horrific thing about these beasties was that they were constructed almost totally around germanium transistors. Also, vast quantities of small polystyrene capacitors. Anybody who has ever worked with these creatures in bulk will know that they do nothing for the system's reliability. These converters were just NOT suitable for use on unattended sites (the digital variant was vastly better in this respect). But staffed sites soldiered on with them to the bitter end.

And, much as we may love them, older 405 sets in working condition were just getting plain scarce. As were dual-standard 405/625 ones, and I can't believe that many people loved them. More particularly, dual-standard 405/625 colour... the first thing I did when BBC1/ITV went 625 was to gleefully decommission the standards-switching gear on my ageing Decca CTV19: a new supply of replacement convergence pots then became available, and weren't they needed. I suppose I should feel ashamed at my actions these days, but back then, it was a different story.

[thyratron]

As I was in the TV repair trade at the time I remember standing to attention with other engineers in the workshop as we watched the engineering announcements ,almost a weekly ritual.
The ITA did a special on the 405 line service in which I remember hearing that they had 'been telling viewers for months' about the closure by putting a caption on the screen.
They did no such thing on the chan 10 from St Hilary apart from one burst at about 11pm in about October 1983.
I remember checking and it was gone again in the morning !
It said somthing like 'THIS SERVICE WILL CLOSE ON JAN 2 1984'
PS. The chan 10 had some hum on picture and was very weak.
All this gave the system a very bad name in the end... and the few customers I had still 405ing were blaming their sets!
I remember around Bath one or two places where there was no Telefusion,no 6&8 VHF, no Mendip and no Bathampton UHF. In the end they organised self help repeaters but some had been on Wenvoe/Rowridge VHF till' the curtain came down!!
THYRATRON

[Ray Cooper]

heatercathodeshort:

...The BBC transmission from CP appeared to retain its very high quality to the very end. I was only a few miles from the transmitter but the sensitivity control on my HMV 900 was never moved from its near minimum position over many years...

Crystal Palace was both in an unfortunate, and a fortunate, position.

Unfortunate, because it was within easy cursing distance of Head Office. The further a tx site got from London, the easier was the life of the incumbents. Up at Sutton, we felt that the heat wasn't on to the same extent (though we were worryingly close to Wood Norton, so kept getting the odd visit from curious engineers and lecturers with bizarre notions of their own to try out). By the time you got to the north of Scotland, Head Office might almost not have existed. I know one site (naming no names) where most H.O. memos went straight to the waste bin, most of them unacted upon.

Fortunate, because CP was a little odd amongst high-power sites. All other HP sites had 50kW main transmitters, 5kW reserves and low-gain TX aerials. CP however had 2x5kW transmitters and a high-gain aerial. It even had, if I remember right, a third 5kW tx that could be substituted for either of the service TXs. A true belt and braces setup, as befitted the station with the highest population coverage and the highest flak quotient.

So, you see, CP still had relatively recent TXs, much easier to maintain than the other HP stuff, and if it went to reduced power would only go down 6dB as against the other sites 10dB. And that 6dB could be reduced to 3dB by a bit of feeder-crosspluggery. And there was always that reserve tx available. Dear me, what a featherbed existence.

[Panrock]

So Ray, that presumably means that CP's e.r.p never dipped below 50 kilowatts, even at the end? No CG1 doing service there then.

Steve

[Ray Cooper]

Panrock:

...CP's e.r.p never dipped below 50 kilowatts, even at the end? No CG1 doing service there then...

I wouldn't have thought so (though I don't know for certain).

The Marconi 5kW gear at CP was later stuff than that installed at other HP sites. Because it ran at much lower tx powers, there was less scope for damaging flash-bang-wallop episodes than occurred on the other sites. Spares were less of a problem. And, to cap it all, they didn't have the pressures on accommodation that the other sites had - at that date, they had no high-power FM services on site, and so when the powers-that-be decreed that most national FM services were to be going mixed-polarisation, there was no need at CP to free up building space for FM re-engineering (going mixed meant doubling the tx powers).

So they would have had little incentive to indulge in such desperate expedients as CG1-ing, I feel.

[ppppenguin]

Originally Posted by Ray Cooper

Somebody mentioned the CO6/501 analogue standards converters. The horrific thing about these beasties was that they were constructed almost totally around germanium transistors. Also, vast quantities of small polystyrene capacitors. Anybody who has ever worked with these creatures in bulk will know that they do nothing for the system's reliability. These converters were just NOT suitable for use on unattended sites (the digital variant was vastly better in this respect). But staffed sites soldiered on with them to the bitter end.

You said that the staffed sites ran with CO6/501 to the bitter end. I'm pretty sure that CP used the digital converters but as you said in a later post, CP was rather a special case. I actually collected a couple of CO6/509 from CP after the close of the service. One unit, along with a lot of spares, was donated to the Vintage Wireless Museum. The other was used in the small museum area at Thorn-EMI Central Research.

Having tried to overhaul the (Pye built, ex ITA) CO6/501A at the Vintage Wireless Museum I now understand why I didn't get very far with it. I think I would have needed to move in for at least a week to make any sensible headway.

[Hybrid tellies]

Originally Posted by thyratron

I remember around Bath one or two places where there was no Telefusion,no 6&8 VHF, no Mendip and no Bathampton UHF. In the end they organised self help repeaters but some had been on Wenvoe/Rowridge VHF till' the curtain came down!!
THYRATRON

I think you must be talking about St Catherines and Northend. We had a few customers out there. My first company (Bristol Wireless) made good use of the RBM A640 dual standards, then at Radio Rentals it was BRC1400's. Both gave good results on Bathamtons ch 6&8. But as you said there was not even a hint of UHF/625 from either Bathampton or Mendip.
I think the Bathampton 405 transmissions came to an end in 1982, before the serious picture problems at Wenvoe started.

[standing wave]

I knew an engineer who was stationed at Crystal Palace at the time of the 405 closure, and one reason he gave for the reliable 405 line service was that the transmitters were left alone while the UHF transmitters were always having new modifications tried out on them by visiting bods from Design Dept. The pictures on Croydon CH9 were certainly very poor towards the end with missing lines etc.
The year before closedown, CH9 would often go off the air during the afternoon for about an hour or so; the reason given for this by the IBA was to find out how many viewers were using the service by the amount of complaints received.
I also never saw any caption radiated by Croydon warning viewers about the closedown of CH9.
Terry.

[Panrock]

Originally Posted by standing wave

The year before closedown CH9 would often go off the air during the afternoon for about an hour or so the reason given for this by the IBA was to find out how many viewers were using the service by the amount of complaints received.

A novel method! I wonder what the results of this survey were...

S