[WARC] Radio Direction Finding

[Len Litvan]

 From http://members.aol.com/homingin/equipment.html

Len  KC0RSX


        Handie-Talkie Tricks

If you are a typical ham radio operator, all you need to get started 
quickly and find foxes successfully is your VHF/UHF handi-talkie (HT) or 
scanner and some simple accessories. The most elementary way is called 
the "body fade" or "body shield" technique. Hold your HT tight against 
your chest and turn around slowly, looking for the direction at which 
your body blocks the signal most effectively (the signal null). At this 
point, the signal is coming from behind you. Walk in the direction of 
the null, taking bearings at regular intervals, and observe the signal 
strength get stronger.

When the signal is so strong that you can't find the null, tune 5 or 10 
KHz off frequency to put the signal into the skirts of the receiver's IF 
passband. If your hand-held is dual-band (144/440 MHz) and you are 
hunting on two meters, try tuning to the much weaker third harmonic of 
the signal in the 70 cm band while performing the "body shield."

Disconnecting the HT's "rubber duck" antenna will knock down the signal 
even more. Hearing the signal with antenna off is usually a "You are 
here!" indicator. Some foxtailers wrap aluminum foil around their HTs to 
attenuate the signal even more. If you do this, be sure to put 
insulating tape over the battery charging terminals on the bottom of the 
set first. You might damage the radio by shorting these terminals with 
the foil.

The "body fade" null, which is rather shallow to begin with, can be 
filled in by signal reflections (multipath), nearby objects, etc. When 
using this method, stay away from large buildings, chain-link fences, 
metal signs, and the like. If you do not get a good null, move to a 
clearer location and try again.