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Re: [Discuss-gnuradio] software controlled antenna

From: Robert McGwier
Subject: Re: [Discuss-gnuradio] software controlled antenna
Date: Tue, 20 Dec 2005 12:50:25 -0500
User-agent: Mozilla Thunderbird 1.0.2 (Windows/20050317)

Chuck that is sweet.  Nice work.


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 ;))


src.write_aux_dac(0,3,value)      0<value<4095

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