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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 10th Sep 2021, 11:10 am   #1
kipperdog
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Default UHF TV transmitter. (Micro UHF Analog TV transmitter).

Came across this novel idea which I thought might interest some restorers:

https://www.tomshardware.com/news/ra...uhf-to-crt-tvs
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Old 10th Sep 2021, 1:33 pm   #2
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Default Re: UHF transmitter

UHF TV transmitters are very illegal indeed in the UK. They're one of the very few items of transmission hardware that it's actually illegal to possess rather than use. I don't know if Ofcom are still as strict about the rules after analogue switchoff, but I wouldn't go down this road without a very good reason indeed.
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Old 10th Sep 2021, 2:16 pm   #3
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Default Re: UHF transmitter

I have heard of the terms legal and illegal but not very illegal.
Aren't UHF modulators (which are transmitters lacking a radiator) used in vintage video recorders and computers?
FM and AM transmitters are also illegal but used carefully and range limited to the locality of the receiver, do no harm to the radio environment
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Old 10th Sep 2021, 2:48 pm   #4
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Default Re: UHF transmitter

Here in the UK years ago you could buy a video sender it had 2 phono connectors 1 for video and 1 for audio the audio was pretty poor and it was not very stable it would drift off tune kind regards Bob
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Old 10th Sep 2021, 3:07 pm   #5
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Default Re: UHF transmitter

Quote:
Originally Posted by kipperdog View Post
I have heard of the terms legal and illegal but not very illegal.
Aren't UHF modulators (which are transmitters lacking a radiator) used in vintage video recorders and computers?
FM and AM transmitters are also illegal but used carefully and range limited to the locality of the receiver, do no harm to the radio environment
There is a difference between a modulator (which does not transmit) and a transmitter.

Quote:
Originally Posted by bobhowe View Post
Here in the UK years ago you could buy a video sender it had 2 phono connectors 1 for video and 1 for audio the audio was pretty poor and it was not very stable it would drift off tune kind regards Bob
The reason there are such strict rules about this is there was a political panic over UHF video senders in the early 80s. These weren't a bridge using non broadcast frequencies like modern examples, but simple UHF transmitters that you hooked up to your VCR or satellite box. Both VHS and Sky were just taking off at the time, and imported video senders were selling in large quantities from unregulated outlets such as market stalls. A full blown regulatory panic ensued, with emergency legislation passed in Parliament making it illegal to possess, never mind use, a UHF broadcast transmitter of any power. A vast range of dubious equipment can be owned in the UK - you can own a 500kW SW transmitter if you want to - but you only commit an offence if you use it without a suitable licence.
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Old 10th Sep 2021, 3:50 pm   #6
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Default Re: UHF transmitter

Quote:
Originally Posted by paulsherwin View Post
Quote:
Originally Posted by kipperdog View Post
I have heard of the terms legal and illegal but not very illegal.
Aren't UHF modulators (which are transmitters lacking a radiator) used in vintage video recorders and computers?
FM and AM transmitters are also illegal but used carefully and range limited to the locality of the receiver, do no harm to the radio environment
There is a difference between a modulator (which does not transmit) and a transmitter.

Quote:
Originally Posted by bobhowe View Post
Here in the UK years ago you could buy a video sender it had 2 phono connectors 1 for video and 1 for audio the audio was pretty poor and it was not very stable it would drift off tune kind regards Bob
The reason there are such strict rules about this is there was a political panic over UHF video senders in the early 80s. These weren't a bridge using non broadcast frequencies like modern examples, but simple UHF transmitters that you hooked up to your VCR or satellite box. Both VHS and Sky were just taking off at the time, and imported video senders were selling in large quantities from unregulated outlets such as market stalls. A full blown regulatory panic ensued, with emergency legislation passed in Parliament making it illegal to possess, never mind use, a UHF broadcast transmitter of any power. A vast range of dubious equipment can be owned in the UK - you can own a 500kW SW transmitter if you want to - but you only commit an offence if you use it without a suitable licence.
Hi Paul this was a transmitter with a telescopic aerial and it had a preset you could adjust from 21 to 68 you are right about market stalls selling them and I did not know that it was illegal to own one thought it was illegal as soon as you use it you learn something new kind regards Bob
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Old 10th Sep 2021, 4:00 pm   #7
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Default Re: UHF transmitter

Surely the important point here is the power output level and how it is conveyed to the set. UHF modulators are in effect very low power UHF transmitters, with good reason, they were intended to seem indistiguishable from any other off-air UHF analogue transmission so that they could be tuned in and 'received' by a set originally only designed to receive off-air broadcast signals.

I (and I'm sure many others) once attached something like a set-top Yagi to the output of a modulator on a home computer or game console out of curiosity, just to see how far it would go. As it turned out, quite far, given the gain supplied by a typical Yagi.

I would imagine these Pi based units would be quite safe to use if the output was attenuated down to the level typically supplied by an analogue RF modulator and cabled, rather than transmitted, to the UHF input of the receiver in question.

Given the potential cost of that TX board plus the Pi and plus any possible extras you might need such as a PSU and SD card, I would tend to solve this problem by using one of the relatively low cost synthesised AV to RF modulators available off the peg - designed for that job, nothing more, nothing less. You can feed one of those from a VCR or DVD player or yes, even the composite video + stereo audio output available on all of the larger Pis.
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Old 10th Sep 2021, 4:49 pm   #8
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Default Re: UHF transmitter

This is an open forum, and also one frequented by all sorts of people, with all sorts of involvement in radio regulatory matters. Not at all suitable for discussing forbidden stuff.
I took 'very illegal' to mean the sort of thing which would be assiduously pursued if it came to light. Assault and battery rather than prolonged parking...

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Old 10th Sep 2021, 6:56 pm   #9
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Default Re: UHF transmitter

As far as I can see it is only a low power modulator chip 200mW similar to what we have in Auroras and Hedghogs, used sensibly it should be possible to use legally to modulate the composite output from your Raspberry pi to feed your 625 line TVs etc the thing to avoid is a long unscreened lead. I think the article was written for an international audience where in many places it would be legal, we just have too be a little more careful to comply with UK rules.
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Old 10th Sep 2021, 7:41 pm   #10
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Default Re: UHF transmitter

Hi Chris as Paulsherwin had said in post it is illegal to own a UHF transmitter dont know if a Aurora or Hedghog converters come in to that category if used transmitter as it was designed as a converter not a transmitter Paul will know better than me. But if the signal radiates outside your property thats a different matter could you get a licence from Ofcom to transmit low power 405 VHF for experimental purpose ? kind regards Bob
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Old 10th Sep 2021, 8:27 pm   #11
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Default Re: UHF transmitter

If you were a manufacturer you could get a test and development licence for a specific
frequency or band. Some years back a defective Freeview box radiated a signal that
lead to a search and rescue op, probably was on the uhf distress beacon channel.
There are licence free video links available at 5.8 GHz for drones and these could be
used to transmit TV (analogue 405, 625, or whatever) over a limited range.
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Old 10th Sep 2021, 9:02 pm   #12
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Default Re: UHF transmitter

Quote:
Originally Posted by Restoration73 View Post
If you were a manufacturer you could get a test and development licence for a specific
frequency or band. Some years back a defective Freeview box radiated a signal that
lead to a search and rescue op, probably was on the uhf distress beacon channel.
There are licence free video links available at 5.8 GHz for drones and these could be
used to transmit TV (analogue 405, 625, or whatever) over a limited range.
Hi that makes sense what Paul said in post 5 about Parliament making it illegal to own a UHF transmitter as UHF is used on the distress beacon channel . Would like to know the outcome of how and what happened when they found out that it was a Freeview box kind regards Bob
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Old 10th Sep 2021, 9:30 pm   #13
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Default Re: UHF transmitter

Wouldn't it have been so much better if an innocuous name like 'Test signal source' had been used rather than transmitter or sender?

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Old 11th Sep 2021, 7:18 am   #14
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Default Re: UHF transmitter

Hello Paul,

In Post #2, you said:

<< UHF TV transmitters are very illegal indeed in the UK. They're one of the very few items of transmission hardware that it's actually illegal to possess rather than use >>

Are you sure about that? Illegal to sell might be closer?
I don't know and I would be keen to understand the actual legal position.

What about analogue amateur 70cm TV transmitters? I have several in my 'collection', two of which I built from scratch (and used) as G6AOE/T many years ago?

Then there's the Marconi drives in the collection from UHF TV transmitters. They are complex units (such as B7400) and are capable in their own right of about 1W output of VSB on frequency. Definitely more than a modulator.
Also a Barco UHF VSB drive for 'local' transmission over cable capable of several hundred mW. A transmitter in all but name.

Even if is the law to not own them, it's unenforceable.
I would have thought that 'illegal to sell' was more likely?

Best regards,

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Old 11th Sep 2021, 8:14 am   #15
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Default Re: UHF transmitter

I don't have the relevant legislation in front of me and am not a lawyer, so I can't quote chapter and verse. The objective was clearly to make it impossible to sell video senders by any means, including privately and at car boot sales. I don't think it was envisaged that the police would be smashing down people's front doors in the dead of night, or raiding genuine museums. Nevertheless, the powers are substantial and did criminalise possession rather than use.

Although the legislation seemed excessive at the time and still does, it was very effective - dodgy imported video senders disappeared from market stalls and independent shops overnight, and have never reappeared.
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Old 11th Sep 2021, 8:33 am   #16
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Default Re: UHF transmitter

It would be interesting to see the actual legislation and a professional interpretation.
If 'illegal to own', there would have been many exceptions - too many.

'Illegal to sell' is much simpler and the 'to own' interpretation may have come from media reports at the time - their own interpretation which would likely be more sensational.

Best regards,

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Old 11th Sep 2021, 9:38 am   #17
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Default Re: UHF transmitter

It is either Illegal or not, if it is indeed Illegal , than do not even think of using.
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Old 11th Sep 2021, 10:07 am   #18
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Default Re: UHF transmitter

Unless the 'to own' legislation was carefully drafted, amateur TV operations on 70 cms would be illegal (they're UHF for sure). Similarly, many large, powerful MATV/CATV installations would likely be illegal too. Neither application is illegal to do - although you need to be a licensed amateur for the former, of course.

I'm very secptical that the law says 'to own' because there's so many potential legitimate uses and users of equipment at least capable of transmission to air.

If it is 'to own', it would have to have been a very carefully drafted piece of legislation.

Best regards,

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Old 11th Sep 2021, 10:17 am   #19
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Default Re: UHF TV transmitter.

The "proposed" ban gets a mention here:-

https://books.google.co.uk/books?id=...SENDER&f=false

This was back in 1988.
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Old 11th Sep 2021, 10:24 am   #20
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Default Re: UHF TV transmitter.

The law is here:
https://www.legislation.gov.uk/uksi/1998/722/made

Specifies 'video sender' - one class of device, I would wager.

Best regards,

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