|[AMRadio] 1930's Old Buzzard Open Rack Transmitter Finally
k4kyv at hotmail.com
Tue Feb 21 18:56:28 EST 2006
>The amount of turns on the link coil impacts what you can load up to a LOT.
>I made my own link for the 812a rig, and had to try various link turns
>it loaded up right. I have the series cap also, and that does change how
>rig loads up, but does not seem to change the efficiency or anything else.
I use a series cap on both my homebrew rigs for 40m and 80m. However, even
with higher capacitance, it wouldn't work on 160. I could hit resonance and
get some loading, but even with the link shoved in all the way, it would
load up maybe 25% of full loading.
Using trial-and-error I eventually came up with a solution that works with
both transmitters. I put two fixed mica caps in series - somewhere about
.0015 mfd each (not out in the shack where I can look at them) - whatever
value it took to resonate the link with the 2 caps in series. I have a 1000
pf variable in parallel with one of the fixed caps for fine tuning. The
coax cable goes across the other capacitor. The link operates as a parallel
tuned circuit, with the load tapped down using a capacitive voltage divider.
With that lashup I can fully load both transmitters on 160 with the link
about 65% into the tank coil.
The series capacitor would probably work on 160 if I had more turns on the
link. Both my links use 4 turns, and I use the same link to load up on 40,
80 and 160. I suspect 8 or 10 turns would do the trick, but then it
probably wouldn't work right on 40. I wired up a switching arrangement
using a 4-pole DT switch to go from the 80/40m circuit to the 160m circuit.
This message was typed using the DVORAK keyboard layout. Try it - you'll
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