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"Mike" =3D=3D Mike Andrews writes:

Jack I'm interested in experimenting with phased arrays, but I can't
Jack find any variable delay lines. I don't want coils of
Jack transmission line -- what I'd like is a little widget that can
Jack be tweaked to change the amount of delay, but I don't see any of
Jack that for analog stuff like transmission lines, just digital
Jack stuff like TTL logic. Help?

Mike We meet in the oddest places, Jack, and this one's as odd as
Mike any. ;=3D)

It's a small world, after all. :-)

Mike For receiving, you could use voltage-biased varicaps; I know
Mike that lots of VCRs use delay lines in which the variable elements
Mike are varicaps, and the first such I encountered was an Ampex
Mike FR-900, back in 1966. Linearity could be a problem, of course,
Mike so you might have to have a DAC doing the biasing based on table
Mike lookup of the desired delay.

The only way I've used variable capacitors (which is what I'm thinking
varicaps expands to) is in antenna tuners. A quick Google doesn't
show any circuits for using varicaps in delay lines, but television
stations apparently used them way back then.

I was considering ADC-digital delay-DAC but I wasn't sure how much
signal quality would be lost in translation. I also must confess I
wasn't exactly sure what sort of voltage/current/etc would be expected
over the transmission line.=20=20

Mike For transmitting, I think even the military use lots of coils of
Mike transmission line, though I'm not privy to the innards of the
Mike modern stuff. Scientific American had an article on phased-array
Mike rigs in Feb. 1985; your library probably has a copy.

While I'd love to build myself a baby elephant cage, I'm afraid I'm
more likely to end up with several "lightning rods" across the top of
my rented abode. I will definitely look into that SciAm article.

Mike -- Mike Andrews Tired old sysadmin since 1964

Jack.
=2D --=20
Jack Twilley
jmt at twilley dot org
http colon slash slash www dot twilley dot org slash tilde jmt slash
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