ch3 video to uhf upconversion
 

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

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

-ex- wrote:
Doug Smith W9WI wrote:

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.

For the most part, USA VCRs or cable boxes have always had a switch for
ch 3/4, or to a lesser extent, 2/3. The way the channel allocations are
done in the US you won't find adjacent channels broadcasting in a given
area so one or the other is supposed to work. Guys halfway between
Philadelphia and New York City will of course explain why thats not
always workable.
Nowadays they have dropped in the digital channels, yes in VHF too, with
no need to regard adjacent channels which turns the cake upside down.
Given the capabilities of modern tuners it makes much more sense to have
selectable UHF channel outputs on consumer gear. There's still some
free slots in the most crowded metro areas...although the "digital data"
people are lobbying hard to get access to those unused frequencies.


-Bill

Hi Bill,
digital here has been a mixed bag - where I am, its line of sight to
the hills which is full of UHF translators - thats not so bad for
analog, as you can "see" the QRM underneath the ch you have chosen as a
RF out. Digital, well, you dont get nothing on screen, so it looks like
the front end of the VCR has died. Took me a while to twig to that one
- even the local agents for a very well known brand didnt know it and
were trying to sell me a new front end to fix the problem!

Hitachi have had OSD of RF frequency out for a while now - Philips also
in some of their tv;s, and TEAC as well, so it will pretty well be
universal before long. The Chinese are really gearing up - they do make
some pretty sophisticated gear, but will happily sell us rubbish if we
want it as well!

We also have a FM broadcast channel on the same tower as the VHF
transmitters - it QRM's TV ch 10 depending on how good the tuner front
end is. - Funnily enough, (well, it isnt really, more obvious) the
older style rotary UHF tuners with ganged RF and LO tuning dont seem to
have any trouble, only the varactor tuned ones. But then, they are the
sweepings of the factory floors of Asia - bought on price rather than
performance. Try telling the customer this tho....

Andrew VK3BFA

Andrew VK3BFA wrote:


-ex- wrote:


We also have a FM broadcast channel on the same tower as the VHF
transmitters - it QRM's TV ch 10 depending on how good the tuner front
end is. - Funnily enough, (well, it isnt really, more obvious) the
older style rotary UHF tuners with ganged RF and LO tuning dont seem to
have any trouble, only the varactor tuned ones. But then, they are the
sweepings of the factory floors of Asia - bought on price rather than
performance. Try telling the customer this tho....

Andrew VK3BFA

The Keyword here is how 'bad' the tuner front end is :) Its probably a
tossup if there's a harmonic being received instead of a mixing beat but
at least tunable sets have a chance of getting away from it.

Here in the US, gear usually has options of off-air, cable, cable HRC
(harmonically related channels) or cable IRC (incrementally related
channels) . Depending on the freq of the FM station *sometimes* you can
force the set away from the FM harmonic by selecting one of the
oddballs. But if its beating with the video there's no cure.

Do you still have folks with rotary tuner sets down there? I haven't
seen one in a customer's home for 30 years on this side!

-Bill

-ex- wrote:
Andrew VK3BFA wrote:


-ex- wrote:


We also have a FM broadcast channel on the same tower as the VHF
transmitters - it QRM's TV ch 10 depending on how good the tuner front
end is. - Funnily enough, (well, it isnt really, more obvious) the
older style rotary UHF tuners with ganged RF and LO tuning dont seem to
have any trouble, only the varactor tuned ones. But then, they are the
sweepings of the factory floors of Asia - bought on price rather than
performance. Try telling the customer this tho....

Andrew VK3BFA

The Keyword here is how 'bad' the tuner front end is :) Its probably a
tossup if there's a harmonic being received instead of a mixing beat but
at least tunable sets have a chance of getting away from it.

Here in the US, gear usually has options of off-air, cable, cable HRC
(harmonically related channels) or cable IRC (incrementally related
channels) . Depending on the freq of the FM station *sometimes* you can
force the set away from the FM harmonic by selecting one of the
oddballs. But if its beating with the video there's no cure.

Do you still have folks with rotary tuner sets down there? I haven't
seen one in a customer's home for 30 years on this side!

-Bill

Hi Bill, nope, not many left with rotary tuners (on UHF) - but I still
get called in to fix them occassionally, and even more so that some of
them still have good tubes in them!

Andrew VK3BFA