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Television Standards Converters, Modulators etc Standards converters, modulators anything else for providing signals to vintage televisions.

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Old 11th Aug 2005, 10:22 pm   #21
Danny
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Default Re: A tantalising possibility

A 4watt set up gives a watchable picture aprox 18 miles from the trancemitter
not that ive done such a norty thing but it would only take a modulator and
a couple of transistors a few caps some copper wire a home made dipole oh and a car battery.
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Old 11th Aug 2005, 11:26 pm   #22
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Default Re: A tantalising possibility

Long, long ago, I remember hearing of someone conducting similar experiments from their chimney with a Ch 1 modulator, an H aerial, and a wide band linear amplifier of undisclosed power...

The erp was sufficient to go tens of miles in favourable conditions. However, due to the throw-height being only ten metres and the house being situated in something of a dip anyway, the signal went for a couple of miles until grinding up against the landscape, at which point it suddenly cut off.
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Old 11th Aug 2005, 11:35 pm   #23
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Default Re: A tantalising possibility

Well I couldn’t stop thinking about this topic all day especially about the 30 line system and how one could broadcast it today. One idea I had was using FM on certain days and times you could broadcast 30 line TV. Knowing very little about electronics I would assume using stereo FM you could use the right channel for the video and the left for the audio, this would then only require one frequency for both vision and audio, shame we don’t have stereo AM in this country! Because now you don’t have to actually build a mechanical set to watch the pictures just a PC with the right software, then you open it up to more people.
As well as broadcasting vintage TV shows and perhaps documentaries you could also use it for more up to date purposes. In fact you could have a special FM station that was more like a documentary station a bit like one of them history TV channels or discovery channels, when its not showing video then it just switches back to stereo audio. Of course the best way would be 2 MW channels as the signal would travel to a much wider audience at night.

Of course 30 or32 line TV has the advantage of the 405 line system being that you don’t need to have expensive equipment to receive it, that’s the beauty of its simplicity. Just a normal radio, PC, software or make your own televisor, maybe you could even record the transitions using cassette tapes ect? (on stereo FM that is) If you tell people they could watch free TV using there normal radio people would be very interested!
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Old 12th Aug 2005, 12:52 am   #24
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Default Re: A tantalising possibility

Quote:
shame we don’t have stereo AM in this country!
Wasn't there some discussion a while back regarding this, the lower and upper sidebands being used respectively for left and right ?

Last edited by Alf; 12th Aug 2005 at 12:53 am. Reason: error
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Old 12th Aug 2005, 6:49 am   #25
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Default Re: A tantalising possibility

Quote:
Originally Posted by Alf
Wasn't there some discussion a while back regarding this, the lower and upper sidebands being used respectively for left and right ?
Going rather OT for the thread here and correct me if I'm wrong, but doesn't/didn't the US stereo AM system do something like this ?

If a British Vintage Television Service in the London area ever came to pass, I think this would be so newsworthy it would generate a lot of publicity for the BVWS and a run on remaining 405-line receivers, including later 'slimlines' and Sony 9 inch.

Steve
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Old 12th Aug 2005, 8:51 am   #26
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Default Re: A tantalising possibility

Well it's all an interesting idea, so what it needs is a miserable old scroat to say why it wouldn't work.

1) How much would the government want for allowing the use of a channel ?
2) How much will it cost for each program re copyright issues.
3) What programmes would you transmit ? Presumably we are talking about a limited couple of hours (say) a week, and I for one would go balistic if flaming sport was broadcast (and I dare say others woudl be miffed if there wasn't some sport!).
4) How much TX power ? 4 watts may go 18 miles but surely that is via a directional aerial ? Remember the huge power and size of Alexander Palace's transmitter which was only really useful for 30-40 miles.
5) Where would you put the transmitter ?
6) Who'd actually run it ? (I bet more than one person needed).

Add all that up and then divide by :-

5) How many people would be able to receive the transmissions anyway ? (not just own working sets but live within range too)
6) How hacked off would those having working sets but live out of range be if, for example, the BVWS did this out of BVWS funds, or worse still increased the subs to achieve it (hack off the radio collectors too).

TTFN,
Jon
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Old 12th Aug 2005, 9:51 am   #27
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Default Re: A tantalising possibility

Well it's all an interesting idea, so what it needs is a miserable old scroat to say why it wouldn't work.

Thanks Jon! This is exactly what we need at this point - seriously. All the answers that follow are of course only my personal opinion and 'straight from the shoulder'.

1) How much would the government want for allowing the use of a channel ?

I don't know. However, for 'heritage' occasional use in an operation run by unpaid volunteers, assuming we were prepared to take our chances and not have the band cleared for our exclusive use, and also reasonably guarantee our limited-power signal wouldn't reach the continent - could it be free ? There is this 70th anniversary of the Television Service coming up too, which would lend national topicality. Maybe even the BBC could put in a good word for us...

2) How much will it cost for each program re copyright issues.

As I understand it, virtually all of our recorded material would be out of copyright. We could add period style presentation of our own. I know some 1930s re-enactors who could conceivably help here.

3) What programmes would you transmit ? Presumably we are talking about a limited couple of hours (say) a week, and I for one would go balistic if flaming sport was broadcast (and I dare say others woudl be miffed if there wasn't some sport!).

This would doubtless be hammered out in discussions beforehand. As I personally see it, transmissions could open with a tuning signal accompanied by something suitable and 'televisiony' like Robert Farnon's "Gateway to the West" from the Guild CD. Then there could be old newsreels and interludes etc... bla bla.. There would be an opening ceremony mirroring that of the service 70 years previously... well I can dream can't I?...


4) How much TX power ? 4 watts may go 18 miles but surely that is via a directional aerial ? Remember the huge power and size of Alexander Palace's transmitter which was only really useful for 30-40 miles.

To be determined. Appropriate power to meet our obligations to prevent interference but hopefully still cover the London area.

5) Where would you put the transmitter ?
At Alexandra Palace, with perhaps a simple vertical dipole as a radiator, not necessarily strapped to the mast. I realise such a discussion is highly cheeky at present, since no one at AP or Harringay has even been sounded out...

6) Who'd actually run it ? (I bet more than one person needed).
A group of BVWS members to meet there every Sunday afternoon ?

Add all that up and then divide by :-

5) How many people would be able to receive the transmissions anyway ? (not just own working sets but live within range too)


Maybe only a handful of viewers (to start) owning 405-line receivers in the London area. But I'll bet with the level of publicity this would attract, many more in this highly populated area would want to climb on board! It would be a non-commercial service so viewer levels shouldn't be an issue (says he).

6) How hacked off would those having working sets but live out of range be if, for example, the BVWS did this out of BVWS funds, or worse still increased the subs to achieve it (hack off the radio collectors too).

A bit like the original debate in the thirties about the radio licence payers subsidising television... Perhaps there could be a vintage television levy or 'licence' paid to the BVWS by those members who were interested. All the more need for a working party to first ascertain the likely costs involved and only give the go-ahead when the figures add up and everyone is happy. I think a guiding principle of the whole project though is to bring in as much support as possible for free.

Another idea might be to make the service available to everyone else who couldn't enjoy it the 'traditional' way over the internet.

Steve
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Old 12th Aug 2005, 10:11 am   #28
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Default Re: A tantalising possibility

And as reality starts to kick in ......As we would be using a frequency currently out of band for TV, I think talk about a regular service is going to sound alarm bells with the authorities far more than a proposal for a one-off.

If a one-off happened, then the gate would have been opened for possible further activity, precedences set, etc. One step at a time perhaps?
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Old 12th Aug 2005, 12:50 pm   #29
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Default Re: A tantalising possibility

Hi all, although I live too far north to support you with "hands on", I may be able to offer advice/ help technically. TV is not really my main interest, but I have experience with radio site engineering (and the kind of red tape you meet with this sort of thing). I suspect that to try and obtain mast space with a commercial operator, you are talking about quite a lot of money, and if you could get a license, it would probably only allow TX powers of a few watts. Better to try and negotiate a privately owned site (someone's roof! with access) with an owner who is into 405 TV! and who is also prepared to only charge you for electricity and not accomodation etc etc etc. Tower locations require antenna riggers, more expense, unless you can get some club formed with subs to pay for these things. Don't let this put you off, I still think it's a great idea.

Biggles.
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Old 12th Aug 2005, 2:58 pm   #30
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Default Re: A tantalising possibility

All sounds ok so far - some sensible objections have been raised - Especially the one relating to spectrum cost.....

As for programming, I would guess that we could also run period advertising (assuming the products/companies are no longer available...) that way we would no be seen to be making a profit.

If I remember the RSL service for radio requires some fairly stringent policy regarding newscasts and so on, but it would be a simple matter to run a test card with world service voice over......

Such a pity I do not remember the original 405 service.......

Would it be reasonable to ask both the committee of the BVWS for some input now as well as APTV - not much point in going further untill a basic agreement can be formed.

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Old 12th Aug 2005, 3:28 pm   #31
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Default Re: A tantalising possibility

Sean

I think you would rather like the band 1 TX down at Dulwich. It's a bit neglected and needs a friend! There is already a "Radio Free Dulwich" aka a MW modulator and length of damp string sending pleasant music round the museum. Now we want "TV Free Dulwich" too

Jeffrey
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Old 12th Aug 2005, 3:46 pm   #32
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Default Re: A tantalising possibility

Hi Jeffrey,

Hmm, you have spotted a weakness of mine..... I do have a penchant for high power RF - none of these three legged fuse things....

I have been down to visit Gerry once, and never spotted the unit there, I would of course be happy to help repair the unit.

I do have a nice ouput bottle here that would work well at 48 MHz, but I think we might be in trouble with the ouput power we proposed - A 3cx3000 will do 7.6 KW when driven correctly.......

Anyway, I look forward to more sensible ideas.....

Cheers
Sean
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Old 12th Aug 2005, 7:38 pm   #33
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Default Re: A tantalising possibility

For 30 line transmissions (not that they ever used Band I for 30 line?) we could probably do it legally by applying for a JFMG - http://www.jfmg.co.uk - point to point link license on one of their Band I frequencies which allow upto 200 Khz bandwidth. I've used these before for a studio to transmitter link for our local RSL station and ISTR the license wasn't very expensive although we migrated to Band III in the end due to continental interference during the summer months.

For 405 line things might be a little more tricky, even assuming we could get the original frequency cleared. It would need to use vestigal modulation to ensure the upper carrier was supressed to stop it interfering with the JFMG allocation.

Checking the OFCOM site shows that the frequencies are currently assigned for military use so getting clearance might be a problem. An alternative might be to use a JFMG video link frequency or use one of the amateur bands (70 cm is the lowest allocation used for amateur TV) although this probably violates licensing conditions? But if you're down-converting the frequency to Band I you might as well just stream something across the net?

Definitely worth a try, though and I'm certainly up for helping out where I can.
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Old 12th Aug 2005, 8:25 pm   #34
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Default Re: A tantalising possibility

Yepp from my point of view, for this to deliver the full 'kick' as a heritage project I really do think any transmissions would have to reproduce the originals as exactly as possible - ie. you turn an old telly on and it works just as it did - this means using the original frequencies, and operating from the original transmitting location would be even better...

Didn't see the military connection when I visited the OFCOM site. But maybe if this frequency is 'assigned' but not actually used in practice by its 'assignee', then it might not be impossible to swing something - there's no harm in inquiring.

On a more dour note I did ask for some negative comments and someone who knows his oats but wishes to remain anonymous has now obliged. Here's what he says:

Seems like a whole lot of people think that a 45MHz TV tx would operate on a spot frequency with no sidebands to cause interference with
neighbouring users. Dream on!

And as it would be double sideband (no VSB filters exist nor could they be fabricated now realistically) you're talking about a signal occupying most of the ether from 40 to 50MHz.

I suspect the BBC would disagree with those who think their material is out of copyright too. Nice idea but totally unrealistic.

Further comments invited !

How does the likely performance of Gerry's transmitter relate to the points made above? As for the BBC point, even if the above were true, if we brought them in at the start, bearing in mind our supporting their next year's 70th, I would of thought we had a sporting chance.

Cheers

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Old 12th Aug 2005, 8:42 pm   #35
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Default Re: A tantalising possibility

Hmm, Not really a positive response that one, however,

I certainly had reailsed that the generation of Video would require approx 4 Mhz of bandwidth as a minimum - The audio is not so serious provided we use a reasonable amount of compression. As for the manufacture of filters, if Amateurs can build filters to put a notch of 60+db, 600Khz apart from the TX frequency at 145Mhz, im sure we could too - its just a question of application of thought and design.

Copyright on material would not be such a serious problem - Some research to who holds the rights to program material, and a polite letter will in most cases get the go ahead provided we identify the original source.

Lets not be dissuaded this early in the project - lets do some proper research first.

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Old 12th Aug 2005, 9:24 pm   #36
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Default Re: A tantalising possibility

Quote:
Originally Posted by m1ecy
Hmm, Not really a positive response that one, however,

I certainly had reailsed that the generation of Video would require approx 4 Mhz of bandwidth as a minimum - The audio is not so serious provided we use a reasonable amount of compression. As for the manufacture of filters, if Amateurs can build filters to put a notch of 60+db, 600Khz apart from the TX frequency at 145Mhz, im sure we could too - its just a question of application of thought and design.
I can't see it being impossible to generate the correct signal either using a suitable BPF or by using some trick DSP? Surely the transmitter Gerry has is VSB capable as I thought only AP used a "full fat" signal? Then again, was the sideband supressed after the final output from the transmitter? Or did they do it at the driver stage and everything was linear thereafter?

More questions than answers from me, I'm afraid.

Quote:
Copyright on material would not be such a serious problem - Some research to who holds the rights to program material, and a polite letter will in most cases get the go ahead provided we identify the original source.

Lets not be dissuaded this early in the project - lets do some proper research first.
Exactly, they can only say "NO" !

Might be worth engaging with the BATC - www.batc.org.uk - if things look positive.
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Old 12th Aug 2005, 9:43 pm   #37
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Default Re: A tantalising possibility

Agreed. If perchance the BVWS does decide to appoint a working party to look further into this project here's an idea of what it might do.

I should think the tasks would be best tackled in this order. All would have to be successfully accomplished for the project to finally be given the go-ahead. No doubt there's still more I haven't thought of too...

To determine the technical feasibility of the project, bearing in mind the human and equipment resources we have to hand.

To contact OFCOM and determine whether Channel B1 might again become available for occasional low power 405-line television broadcasts and if so, what the technical requirements and the costs would be.

To evaluate archive programme material that could be used and determine its copyright status.

To contact the relevant authorities controlling the 'television' wing at Alexandra Palace, find out whether it would be possible to conduct this project from their premises and if so what their terms would be.

To summarize the likely overall cost and commitments of time required and decide whether these could be met.

Then, if all the above were satisfied and it was still 'go' for takeoff:

To contact the BBC, outlining our plans, and find out if they might like to mark the 70th anniversary of their television service in conjuction with us.

Still just ideas, and still just a pipedream ...

Steve
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Old 12th Aug 2005, 10:14 pm   #38
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Default Re: A tantalising possibility

AFAIK, Gerry's TX is a proper VSB system. I haven't looked at it in enough detail to see the filters but can't imagine that even a low power relay would have been allowed to radiate full double sideband.
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Old 12th Aug 2005, 10:42 pm   #39
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Default Re: A tantalising possibility

I feel A visit to Dulwich coming on........
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Old 12th Aug 2005, 11:24 pm   #40
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Default Re: A tantalising possibility

wouldnt we need two txs one for vision and one for sound .
I thought it was done this way using a conbiner unit to match both signals to the dipole. i have a book on the subject i will dig it out and have a recap it has some information on txs as well
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