[hpsdr] Direction Finder using Dual-Mercury Diversity Operation

[Curt, WE7U]

On Thu, 22 Sep 2011, Steve Bunch wrote:

> You could use a PIN diode switch to switch between two antennas at a rapid rate.  If you synchronize that switching with gathering a block of samples from the A/D, say, with an output pin driven by Mercury, so the signal processing knows which antenna generated which samples, you could create an approximation of diversity.  Basically alternating doing the FFT/processing on each set of samples under the assumption that the signal you're homing in on is fairly constant across 2x the sample period so you don't mind missing every other block.
> I think you'd be able to approximate the in-between block ok for near-constant signals by interpolating the FFT bin values, or reconstruct a single signal by grabbing blocks at above the
Nyquist rate and filtering -- but I'm no expert.

> You have to compromise between sample block length and switching frequency, obviously.  You probably wouldn't be able to use it to listen to fast CW, but you could do DF'ing with it.

Revise that slightly to use four antennas, with two digital outputs from the Mercury driving four PIN diodes (base of each antenna) and you've got a full-blown DF'ing system for about $1.99.  Not including the $1000+ for the OpenHPSDR system and the four antennas & coax of course!

S/W could do a much better job analyzing the doppler tone/displaying the direction than a bunch of TTL and 16 LED's (per the 1978 DoppleScant article).

Does the multiple Mercury card setup give a narrower beamwidth, at additional cost/complexity?

-- 
Curt, WE7U.        http://www.eskimo.com/~archer
APRS:  Where it's at!        http://www.xastir.org

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