Hi all,

It's me again, attempting yet another mad science project, and I have
practically googled the subject to death before thinking of asking this
group for help:

I am wanting to put video (preferably color but will settle for
grayscale) onto a UHF TV channel for inhouse use only. I am
considering doing it as follows:

1) Convert output of a VGA card to composite video using resistive
combiner
(found a few on net).

2) Place composite video on VHF channel 3 using a game modulator.

3) Upconvert the video signal on VHF to UHF by with a local oscillator
whose frequence is the difference between the channels. I'd use an
active mixer circuit from the VHF/UHF part of the Handbook to do this.

4) To test functionality, attempt to tune in using either an analog TV
receiver or a TV tuner card.

Question is this:

Is point 3, upconverting video from VHF to UHF, a generally workable
technique?

Any other gotchas or pitfalls to my intended approach?

Thanks in advance,

The Eternal Squire

wrote:
Hi all,

It's me again, attempting yet another mad science project, and I have
practically googled the subject to death before thinking of asking this
group for help:

I am wanting to put video (preferably color but will settle for
grayscale) onto a UHF TV channel for inhouse use only. I am
considering doing it as follows:

1) Convert output of a VGA card to composite video using resistive
combiner
(found a few on net).

2) Place composite video on VHF channel 3 using a game modulator.

3) Upconvert the video signal on VHF to UHF by with a local oscillator
whose frequence is the difference between the channels. I'd use an
active mixer circuit from the VHF/UHF part of the Handbook to do this.

4) To test functionality, attempt to tune in using either an analog TV
receiver or a TV tuner card.

Question is this:

Is point 3, upconverting video from VHF to UHF, a generally workable
technique?

Any other gotchas or pitfalls to my intended approach?

Thanks in advance,

The Eternal Squire

The easiest way is to gt a hard rubbish vcr, (most have been dumped
because of tape transport faults) use the av inputs, and output on a
UHF channel - the modern ones have tunable UHF output.

73 de VK3BFA Andrew

Did some research on Alps UHF modulator, these are limited to channels
30 - 37. I am wanting more channel range, but these would be
good for experiments I suppose.

What I want is to ask if upconverting the HF television signal to the
center frequency of the UHF channel would have the same overall effect
as using a direct modulator.. The physics says probably yes, but are
there any showstoppers other than physics?

The Eternal Squire

wrote:
Did some research on Alps UHF modulator, these are limited to channels
30 - 37. I am wanting more channel range, but these would be
good for experiments I suppose.

What I want is to ask if upconverting the HF television signal to the
center frequency of the UHF channel would have the same overall effect
as using a direct modulator.. The physics says probably yes, but are
there any showstoppers other than physics?

The Eternal Squire

Converting TV channels - even upwards to UHF - is commonplace in cable
and MATV systems. I would skip the chanel 3 conversion and go straight
modulator to UHF if I were you unless you have a need for the ch. 3 signal.

A modulator which tunes the entire band does add to the cost. You can
get commercial units that tune all channels if thats a necessity.

I was just thinking...remember the "Rabbit" system that was popular
about a decade ago? It was used for transmitting a signal from your VCR
or sat rcvr to other sets in the house. I can't recall if it used UHF
or some proprietary frequency. That might be worth looking into.

GL,
Bill

Andrew VK3BFA wrote:
The easiest way is to gt a hard rubbish vcr, (most have been dumped
because of tape transport faults) use the av inputs, and output on a
UHF channel - the modern ones have tunable UHF output.

Not in the States. VCR modulators here output on VHF channels 3 or 4.
(60-66 or 66-72MHz)

If the OP can find a foreign UHF modulator, it should work with US
signals, with two possible issues:

- The sound-video separation is different. This means the sound will be
on the wrong frequency for an American TV. If the OP doesn't care about
sound then this isn't a problem!

- TV channel frequencies are different in different countries. Most
Australian channels don't coincide with American channels. (if a
modulator tunes Australian channels 30-37, the only channel in that
range that corresponds to an American channel is 32, which is American
channel 28)

Are European/Australian VCR modulators continuously tunable? Or can
they only be set to discrete channels?

http://www.73.com/a/0019.shtml offers a "block converter". (among
dozens of other items! It's about 3/4 down the page on the left-hand
side, stock #AE047) It's a broadband frequency converter that will
convert a US channel 3 RF signal up to US channel 37.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Doug Smith W9WI wrote:
Andrew VK3BFA wrote:
The easiest way is to gt a hard rubbish vcr, (most have been dumped
because of tape transport faults) use the av inputs, and output on a
UHF channel - the modern ones have tunable UHF output.

Not in the States. VCR modulators here output on VHF channels 3 or 4.
(60-66 or 66-72MHz)

If the OP can find a foreign UHF modulator, it should work with US
signals, with two possible issues:

- The sound-video separation is different. This means the sound will be
on the wrong frequency for an American TV. If the OP doesn't care about
sound then this isn't a problem!

- TV channel frequencies are different in different countries. Most
Australian channels don't coincide with American channels. (if a
modulator tunes Australian channels 30-37, the only channel in that
range that corresponds to an American channel is 32, which is American
channel 28)

Are European/Australian VCR modulators continuously tunable? Or can
they only be set to discrete channels?

http://www.73.com/a/0019.shtml offers a "block converter". (among
dozens of other items! It's about 3/4 down the page on the left-hand
side, stock #AE047) It's a broadband frequency converter that will
convert a US channel 3 RF signal up to US channel 37.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Hi Doug,
thats interesting - us in OZ had the same VHF output system years ago,
but when we got UHF broadcasting, all the VCR's went to UHF output.
Most (if not all) are tunable over a narrow range,(via a trimmer cap on
the rear panel) some of the more exotic ones (even from dumpster
diving) have user settable(sp) output with the actual RF frequency on
screen - makes a crude UHF sig gen.

The advantage of the UHF output over the older VHF only is no
co-channel QRM from the strong Ch3 signal to local on air channels.
Agree with the different standards - nowadays, this is not an issue as
even the el cheapo VCR's are multi-standard. Saves having to
manufacture for different markets, and the new chipsets for this are
dirt cheap. Most new ones have an integrated tuner/if/video conversion
"can" - unfortunately, bus controlled so difficult to experiment with
unless you are comfortable with microprocessors. I aint - firmly rooted
in the analog domain!

73 de VK3BFA Andrew

Andrew VK3BFA wrote:
thats interesting - us in OZ had the same VHF output system years ago,
but when we got UHF broadcasting, all the VCR's went to UHF output.
Most (if not all) are tunable over a narrow range,(via a trimmer cap on
the rear panel) some of the more exotic ones (even from dumpster
diving) have user settable(sp) output with the actual RF frequency on
screen - makes a crude UHF sig gen.

UHF in the States long predates the VCR. But that may be why we stuck
with VHF output -- because early UHF tuners were pretty bad and many
Americans had experience with their poor stability and difficult tuning.

So the VCRs with on-screen frequency setting are also continuously
variable? I mean, you can select a RF frequency that doesn't correspond
to a valid Australian channel?

The advantage of the UHF output over the older VHF only is no
co-channel QRM from the strong Ch3 signal to local on air channels.

True. (though with the dawn of digital TV in the States I'm not so sure
that's enough anymore! Here in the Nashville area we have stations on
channels 20, 21, 23, 24, 26, 27, 28, and 30 among many others...)

Cable TV boxes use the same modulators as VCRs. CBS-TV had a serious
problem when they began digital broadcasts in Chicago a few years ago.
They'd been assigned channel 3 for their digital transmitter, and it
clobbered the cable boxes. Of course, QRM on the boxes' output channel
meant that it clobbered *every* channel on the cable!

Agree with the different standards - nowadays, this is not an issue as
even the el cheapo VCR's are multi-standard. Saves having to
manufacture for different markets, and the new chipsets for this are
dirt cheap. Most new ones have an integrated tuner/if/video conversion
"can" - unfortunately, bus controlled so difficult to experiment with
unless you are comfortable with microprocessors. I aint - firmly rooted
in the analog domain!

Multistandard equipment is more common in the US than it used to be, but
it's still pretty rare. I only know of two variants of NTSC - the one
used in Japan, and the one used in all other NTSC countries including
the US - and they vary only in the RF carrier frequencies used. (even
sound-vision separation is the same) Still, American equipment cannot
(usually) be switched to receive Japanese frequencies.

Yeah, my microcontroller experience is pretty limited as well!

--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

On Sun, 12 Jun 2005 13:41:29 GMT, Doug Smith W9WI
wrote:

[snip]

http://www.73.com/a/0019.shtml offers a "block converter". (among
dozens of other items! It's about 3/4 down the page on the left-hand
side, stock #AE047) It's a broadband frequency converter that will
convert a US channel 3 RF signal up to US channel 37.

I called these bozos to inquire about buying one of these. You get an
answering machine but not the courtesy of a call back. The items have
also disappeared from their web site inventory.

Any other sources?

Wes N7WS

One pitfall not already mentioned is that simply combining the R-G-B and
sync signals coming out of a VGA card won't produce a US standard NTSC
signal. A US television signal (NTSC compatible) uses a 15.750 kHz
horizontal sweep rate. The lowest VGA resolution (640 X 480) uses a 31.5
kHz sweep. Higher resolutions use higher sweep rates. This scan rate
incompatibility may complicate your project. Of course, there are some
specialty video cards around that have an NTSC video output, in addition to
VGA. Those cards have an on-board scan converter.

Good luck,

Roger K6XQ

Roger,

Wouldn't this be be exactly double of NTSC, in which case the TV would
see every other frame of the composited VGA? Or, because I am
intending to run the card in Linux, could I create a resolution below
640X480? But you may be right, a surplus video card with S-video out
would sidestep this problem.

The Eternal Squire