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March 23rd 04, 11:46 PM

On 23 Mar 2004 12:45:15 -0800, (Tom Bruhns) wrote:

Hmmm...I simulated it, and it looked fine to me. I don't do a.b.*
groups. I haven't actually built one; more pressing things to do.
But I expect it will work OK. It assumes no inductive coupling among
the coils. That's usually not too hard to get low enough in practice,
if you orient the coils properly.

BTW, check out Coil-Q inductors for commercial RF coils in small
shield cans with decent Q. 7mm square can, Qu around 100 for
inductances and frequencies in the neighborhood we're talking about
here.

Hey, give me a chance to keep up with your suggestions, will you? ;-)
I've only just today taken delivery of some powedered iron toroids you
tipped me off on (T37-10 for the time being) and am experimenting with
those at present. Moreover, I replaced the factory, miniature,
resistor-like inductors in my original 5X multiplier with hand-wound,
air-cored ones for better Q, and guess what? *Huge* difference!
Couldn't get a fifth *at all* before, as you may recall, but changing
the inductors for the higher Q construction really brought it on big
time! So much so I was convinced I'd made some fundamental mismeasure
with the test equipment settings. Eventually it dawned that there was
no error. The whole problem had been down to choice of coils - same
values alright, but very different Qs. I've you to thank most
sincerely for that revelation!
Though the transistor-based multiplier and buffer/amp now works great,
I'll still stick with your series filter solution as it saves on
transistors and other components too. Just one last query, Tom: in
your design between the ouput of the first inverter and the input to
the next, you have, in series, a 0-10pF variable cap and a 20uH coil.
Then you have your DC bias to the 2nd gate input and a 15pF cap
shunted to ground at the same point. What was the purpose of that 15pF
cap? Was it to provide an AC ground, bypassing the lower resistor (the
one from input to gnd) or was there some loading function involved
with it as well? Or was it intended to allow some independent control
over the signal voltage level to the 2nd inverter input?
Thanks again,

Paul

--

The BBC: Licensed at public expense to spread lies.

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