RF modulator connections

ivan ) wrote:

: The problem with most older VCRs is that they only output channel 30-39.
: I use a relatively readily available, and free! quite compact Pace analogue
: satellite receiver (to feed a surveillance camera around the house) the
: output of which covers the UHF band, and allows one to programme the
: required channel output in the on-screen menu.
: However it still requires a SCART input, which begs the question, how did
: you manage when you used the video?


I've been cannibalising the old VCR for electronic parts for years, so
what I'm talking about is just the modulator, which is a bought-in
unit from Jalco. It's often surprisingly easy to find spec. sheets
for even elderly components on the web, but not this time....

--
Steve Blinkhorn

Alex Bird ) wrote:
: "Richard" wrote in message ...

: Although cannibalising a modulator from a dead Vcr seems a good idea, just
: knowing the connections may not be enough. For example what is the default
: UHF channel for it's output? How can this be changed if necessary? Are the
: input/output levels automatically controlled by the module or by external
: circuitry? I think that you need to get hold of the manufacturer's data
: sheets for these and other data before getting too involved.

: It is a good idea! I've used it many times. BUT you need a
: modualator from an older VCR, or one with an old design. These
: commonly have inputs labelled A, G, V, +; can you guess what those
: are?? The input voltage seems to be 5,6,9 or 12 volts. Start low and
: up it if it doesn't work. Some have two power connections, one for
: loop-through and one for the modulator so connect both. Really old
: vcrs have separate loop-through and modulator gubbins, so if you need
: you'll have to use and power both. There are often adjustments for
: sound and video modulation level, accessable through the screening.
: It sounds like the modulator you have is integrated too tightly with
: the control logic of the vcr, or possibly doesn't handle all the
: modulation on board. Perhaps it was tunable throughout the UHF band.
: I think you'll be lucky to scavenge and use one with that capability.

Well, it's tunable via what I take to be a trimmer capacitor; and it
looks to me as if it is precisely designed as a buy-in. Loop through
is on board. My *guess* is that AD and VD are audio and video
inputs, which should be at standard levels (e.g. 1V peak-to-peak
video). Since video modulation is usually negative, I'm guessing
that I need to supply a reference positive voltage, and that the other
connection with a + in it is the DC supply. But I was hoping someone
could point me at a document...


--
Steve Blinkhorn

(Steve Blinkhorn) wrote in message ...

Well, it's tunable via what I take to be a trimmer capacitor; and it
looks to me as if it is precisely designed as a buy-in. Loop through
is on board. My *guess* is that AD and VD are audio and video
inputs, which should be at standard levels (e.g. 1V peak-to-peak
video).

I suspect you're right, when I saw those abreviations at first I
thought they were totally random, and you'd pulled some sort of
monster out! Suggest you experiment as the replacement cost is
minimal.

The additional +ve supply may power the loop through, when the vcr is
off, as mentioned before. Modulation is prob. an internal trimmer.

Alex