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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 4th Mar 2015, 11:32 am   #1
neville23
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Default Is there a use for a vestigial sideband modulator?

Can anybody think of a use for a UHF, crystal controlled modulator with a proper sideband filter? Are there any countries in the world that haven't gone digital?
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Old 4th Mar 2015, 1:11 pm   #2
cmjones01
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Default Re: is there a use for a vestigial sideband modulator?

If everyone's gone digital, that means that analogue is now vintage, so keeping old analogue sets running will need modulators like that.

Analogue distribution is still used, though: I stayed in a hotel at the weekend which had the local DVB multiplexes on the TV, but also had some channels distributed from satellite receivers as analogue channels. That meant the (ordinary domestic) TV in the room used both its digital and analogue tuners.

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Old 4th Mar 2015, 1:24 pm   #3
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Default Re: is there a use for a vestigial sideband modulator?

If the frequency could be altered down to 437 MHz approx., it could be used for amateur
TV (licenced) although even here narrow bandwidth DTV has become more standard.
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Old 5th Mar 2015, 9:06 pm   #4
neville23
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Default Re: Is there a use for a vestigial sideband modulator?

It could be moved down. There are dip switches in the LO PLL, and 00000000 gives 512MHz, but there are two more switch positions that are hard wired; These must be 512MHz (on) and 1024MHz (off).

The sound subcarrier is tuneable, but the notch in the video at 6MHz is a ceramic filter. It could be changed if necessary.

Any suggestions for a forum to post it in? It should really go to a broadcast situation.
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Old 7th Mar 2015, 9:07 pm   #5
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Default Re: Is there a use for a vestigial sideband modulator?

Just the sort of thing I'm looking for, but for VHF mainly. I've been looking at building filters but will need the help of a good friend who is a radio HAM. Looking at those filter design programs the required precision is probably a bit out of my league! .. and the commercially available ones are, financially.


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Old 8th Mar 2015, 9:21 am   #6
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Default Re: Is there a use for a vestigial sideband modulator?

beware of filter design programmes, even the pricey ones have no sense of reality. They quite happily lead you into architectures that won't be realisable. For example a firm did a subcontract design, and used computer generated filter designs by a reputable microwave analysis package.

Unfortunately the filters when built were a long way off song. The architecture chosen was sensitive to stray C to ground on a few particular nodes, and even 0.5pf stray from the surface mount pads and a couple of mm of track was too much.

It's common to also wind up with inconveniently large iinductor values such that inter-winding capacitance wrecks things.

The programmes DO work, but you need to know enough to design the filter yourself to be able to make them give you a working result.

Once you are at that level, you can do the filter with a book and a pocket calculator. The computer is nice for a simulation as a check.

What do you need?

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Old 8th Mar 2015, 11:32 am   #7
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Default Re: Is there a use for a vestigial sideband modulator?

The amateur TV forum is here: http://www.batc.org.uk/forum/
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Old 10th Mar 2015, 2:47 am   #8
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Default Re: Is there a use for a vestigial sideband modulator?

Quote:
Originally Posted by neville23 View Post
Can anybody think of a use for a UHF, crystal controlled modulator with a proper sideband filter?
You could use it to distribute an analogue TV channel round your home. I have 5 VSB modulators doing just that. The ones I have are on E2, E4, S18, 58, and 61. They were made by SPT Video of Malden in Essex (long gone). I also have a matching Nicam encoder on the Ch 61 one.
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Old 4th Apr 2015, 2:00 am   #9
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Default Re: Is there a use for a vestigial sideband modulator?

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Originally Posted by winston_1 View Post
I also have a matching Nicam encoder on the Ch 61 one.
Was that an industrial model? I was vaguely under the impression that the makers of consumer VCRs and other AV products with modulated RF outputs had agreed that only mono sound would be transferred this way, and that they would not use any stereo or two-channel coding.

Still, an intriguing thought is an Aurora-like device that could encode and modulate the several forms of stereo/two-channel TV sound. I think it would be quite complex, though, covering at least the B/G/H, I and L NICAM variants, the B/G/H, D/K and M Zweiton variants, Japanese FM/FM and American MTS. I suppose too that one might reach back to the French dual-channel system used in Algeria in the 1950s.

Cheers,
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Old 15th Apr 2015, 10:14 pm   #10
winston_1
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Default Re: Is there a use for a vestigial sideband modulator?

The nicam encoder is a professional 1U unit that was used by cable companies at their head ends.
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