All,

To transmit a video signal on a UHF or cable television channel
(signal will be low power and transmitted along a shielded wire to
other equipment), is all I need to do is mix an baseband video signal
(S-video) with the carrier of the channel in question? Or, is there
something more I need to do?

wrote:

To transmit a video signal on a UHF or cable television channel
(signal will be low power and transmitted along a shielded wire to
other equipment), is all I need to do is mix an baseband video signal
(S-video) with the carrier of the channel in question? Or, is there
something more I need to do?

Not quite. In general TV signals are LSB reduced carrier with the audio as
an FM signal. The exact spacing between channels, and audio carrier frequency
varies from country to country. France uses AM audio.

ATV signals in the 430 mHz band are the same as TV signals, 1.2gHz and up use
FM video. I don't know about the 900 mHz band.

The easiest thing to do would be to take the modulator out of an old VCR.

Geoff.

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

On Sat, 27 Oct 2007 12:41:06 -0700, eternalsquire wrote:
To transmit a video signal on a UHF or cable television channel
(signal will be low power and transmitted along a shielded wire to
other equipment), is all I need to do is mix an baseband video signal
(S-video) with the carrier of the channel in question? Or, is there
something more I need to do?

S-video is a component signal - it splits the chroma and luma. You're
going to have to reassemble them before you can modulate it on a RF
carrier, if you want a standard TV to receive it.

I don't think most amateur TV stations use a VSB lower-sideband filter.
They seem to work OK - though they're generally going for legibility, not
high picture quality!

The other suggestion, that you use a modulator from an old VCR, is a good
one. In America that'll be VHF instead of UHF.

Doug Smith W9WI ) writes:

I don't think most amateur TV stations use a VSB lower-sideband filter.
They seem to work OK - though they're generally going for legibility, not
high picture quality!

The other suggestion, that you use a modulator from an old VCR, is a good
one. In America that'll be VHF instead of UHF.

I don't know what's being used nowadays, but it is interesting how it
has been in the past.

Up till 1976, pretty much all articles about ATV would be about high
level modulating an existing transmitter. Do it that way, and the
only way to get VSB is with a filter that can tolerate the power level.

The one exception I've seen was an early sixties article in QST where the
author (a QST staffer if I recall) took the modulated RF output of a
surveillance camera and fed it into an upconverter to get up to UHF.
Likely that wasn't used much since it was more complicated.

Then in 1976, there was an article in "Ham Radio" about modulating
an oscillator running at about 50MHz, and then converting it up
and using a linear amplfication chain. More complicated but likely
put out a better signal than most ATV transmitters at the time. I
seem to recall there was even an LC VSB filter at the "IF" frequency.

I would have thought by now it had switched over to that sort of
thing, but I don't really know.

A lot or most of those RF modulators I've looked at have an SAW
filter, so I assume the output is close to VSB. Feed it into a
mixer stage, then some stages of linear amplification and there
you go.

Michael VE2BVW

On Oct 27, 10:33 pm, (Michael Black) wrote:
Doug Smith W9WI ) writes:

I don't think most amateur TV stations use a VSB lower-sideband filter.
They seem to work OK - though they're generally going for legibility, not
high picture quality!

The other suggestion, that you use a modulator from an old VCR, is a good
one. In America that'll be VHF instead of UHF.

I don't know what's being used nowadays, but it is interesting how it
has been in the past.

Up till 1976, pretty much all articles about ATV would be about high
level modulating an existing transmitter. Do it that way, and the
only way to get VSB is with a filter that can tolerate the power level.

The one exception I've seen was an early sixties article in QST where the
author (a QST staffer if I recall) took the modulated RF output of a
surveillance camera and fed it into an upconverter to get up to UHF.
Likely that wasn't used much since it was more complicated.

Then in 1976, there was an article in "Ham Radio" about modulating
an oscillator running at about 50MHz, and then converting it up
and using a linear amplfication chain. More complicated but likely
put out a better signal than most ATV transmitters at the time. I
seem to recall there was even an LC VSB filter at the "IF" frequency.

I would have thought by now it had switched over to that sort of
thing, but I don't really know.

A lot or most of those RF modulators I've looked at have an SAW
filter, so I assume the output is close to VSB. Feed it into a
mixer stage, then some stages of linear amplification and there
you go.

Michael VE2BVW


I am actually trying to send the output of a video card to a CATV
channel.
I have VGA, S-Video, and RCA TV-out for choices.

wrote:
I am actually trying to send the output of a video card to a CATV
channel.
I have VGA, S-Video, and RCA TV-out for choices.

I don't know where you are, but since you are posting from comcast, I'll
hazzard a guess that you are in the U.S.

My suggestion to you is to go to Radio Shack, or a store similar to what
they used to be and buy a modulator for a video game or DVD player.
You may be able to find one at a second hand sale, Salvation Army,
Goodwill, etc.

Take the composite output (RCA socket TV-out) and plug it into the
modulator and be done.

The VHF ones are usually fixed to channel 3 and 4 (with a switch), the
UHF ones are usualy tunable, but you may be able to "tweak" them.

Geoff.`


--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/

On Oct 29, 9:14 pm, (Geoffrey S. Mendelson) wrote:
wrote:
I am actually trying to send the output of a video card to a CATV
channel.
I have VGA, S-Video, and RCA TV-out for choices.

I don't know where you are, but since you are posting from comcast, I'll
hazzard a guess that you are in the U.S.

My suggestion to you is to go to Radio Shack, or a store similar to what
they used to be and buy a modulator for a video game or DVD player.
You may be able to find one at a second hand sale, Salvation Army,
Goodwill, etc.

Take the composite output (RCA socket TV-out) and plug it into the
modulator and be done.

The VHF ones are usually fixed to channel 3 and 4 (with a switch), the
UHF ones are usualy tunable, but you may be able to "tweak" them.

Geoff.`

--
Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog athttp://geoffstechno.livejournal.com/

I want to build a tunable UHF modulator for myself. If I wanted to
be an appliance
operator I would not be posting on this newsgroup.