[K4RY] Direction Finder

[Kris Kirby]

On Sat, 15 Sep 2012, John Klingelhoeffer wrote:
> Nicely done! Allow me to make a suggestion based on experience:  It is 
> *extremely* difficult for the human ear to hear a 'peak' or a 'null' 
> in an audio tone's amplitude.  Two possible extensions to your project 
> to overcome this:
> 
> The first is to take the audio output of the HT from the earphone 
> jack, run it through a precision rectifier (op amp with diodes in the 
> feedback loop) and then drive an analog meter movement with the 
> filtered DC output.  
> 
> Or, use the same precision rectifier to drive a voltage to frequency 
> converter, so the output is a varying frequency audio tone rather than 
> a varying amplitude (sort of like a theremin!).  Either should provide 
> a better (and faster) null or peak indication than the ear.

My understanding was that the device causes an audio signal to be 
generated in the received audio. From there, I believe you can commutate 
the audio signal to a filter and a tone detector to get a 
signal/direction. 

If you're aware of SDR, you can see how this can get really deep as you 
sample I/Q for each of four antennas, then post-process the signals, 
compare against other antennas, and correct/resolve phase shift and 
Doppler.  Then you have to figure out how to do that in the other 
polarization at the same time, and resolve linear vs circular. ;) Lots 
of receivers (8) and horsepower, so you can hear 360-degrees and track 
at the same time. Even resolve speed from the Doppler.

I wonder if/how one could resolve the switching action of the diode as a 
monopulse tracking feed - like result. Certainly easier with 90-degree 
sector antennas, and a solid backing plate. 

OTOH, if you need a null on one side, the Moxon will do that, but cannot 
be in the vicinity of other metal or the null will be detuned. 

Why all this? So I can hear APRS on both sides of the mountain at once, 
from the ridge top. 

--
Kris Kirby, KE4AHR
Disinformation Analyst