Rich,
..
>? RF-switching shifts to non-linear bias during soft syllables. The
>amplifier's T/R bias should always be in sync with the T/R state in the
>transceiver.
Agreed. I'm tempted to rebuild the original board just to be
able to look at it with the spectrum analyzer, but it probably
isn't worth the trouble. My DSO/analyzer only goes to
16mhz anyway, (32mhz sampling) so I couldn't test it beyond 20m.
>? 8 - 10 % drop is more likely for a C-filtered PS. .
Okay, then make it 3900/3510 . I found the CC curve sheet for
the 8877 on a site somewhere, but have no idea what idling
current (thus first-approximation bias voltage) Eimac recommends
for a 8877 in a GG AB1 configuration at that anode voltage. Any
ideas?
>? The high-speed switching circuit shown in Fig, 7B on my web site
>switches in under 2mS and it supplies adjustable bias for g-g operation.
>It switches so fast that sequencing is obviated.
I took a look, thanks. I don't know what flavor the existing
output vacuum relay is, but the printing on it is "TCR1G N/O 7404" .
It doesn't look like a Jennings, but I've made larger mistakes.
Anyway, your bias switch design looks fine, and would fit on a
board the size of the existing one. Even 18 or so 3A diodes,
(tapped down) although I've heard stories of temperature
instability going that route? (A question, not a challenge.
Haven't done it that way before)
>..
>? mo' complicated is not always mo' betta.
.
>? chips and RF don't get along all that well.
True enuf. Using a packaged uC module, the total parts count
wouldn't have to be much higher, but it would have to be well
shielded and bypassed. I'll consider both routes thoroughly
before taking one.
Thanks,
Jim Barber, N7CXI
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