Chuck that is sweet. Nice work.
Bob
N4HY
Chuck Swiger wrote:
This weekend's project was pretty easy and useful. My indoor antenna
is a loop
with pretty sharp Q which requires touching up, manually, even if
receiver frequency
is changed only 50kHz. I have to get up, walk over to the loop and
turn a 365pf variable
cap to 'peak' the signal.
I just found out about MVAM109 varactors, which go from about 40 - 400
pf with
0-9vdc bias, so it was fairly easy to use the gnuradio/usrp aux DAC
'D', the sigma
delta, which is brought out on J17 on the basic RX board, and makes
0-3.3 vdc
with 12-bit precision, a 2N2222 transistor dc amp with a 12v supply to
boost it
up to 0-9vdc. Put two MVAM109's back to back on the loop fed thru 100k
resistors
(they're very high Z) and now I can adjust and peak the antenna with a
slider on the gui ;))
--Chuck
http://partsandkits.com/MVAM109.pdf
src.write_aux_dac(0,3,value) 0<value<4095
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--
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats
Laziness is the number one inspiration for ingenuity. Guilty as charged!
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