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