[FedCom] Direction Finding Techniques for Fedcom Freqs?

[gary]

Directional antennas aren't as useful as you would think in T-hunting. 
Generally a device that uses a null works better, i.e. you can make 
sharper nulls than you can a directional beam.

I have one of those home brew DFs that use a bow tie antenna and a 
analog gate to switch between sides of the bow tie. I know it works at 
VHF, but I don't know about UHF.

This is close to what I have:
http://www.handi-finder.com/

One idea might be to use a loop antenna. In HF, this works great. You 
are using what is knows as a "small loop".

Getting back to a direction antenna approach, you can use one with an 
attenuator. The idea is to get the system (radio, antenna, attenuator) 
to the point where it only find a signal in one direction. That is, the 
loss is the attenuator is so great that the signal is not detectable 
except in one direction. The problem with a directional antenna, is that 
at the sides (if vertically polarized) you just have a dipole. So it is 
not like you have no gain at the sides, but rather the antenna falls 
back to the gain of a dipole, and that has plenty of signal strength to 
  detect.


Ken wrote:
> Interesting challenge.  I'd assume that "signal stalker"/"close call 
> capture" technology would work on digital encrypted signals.  I know on 
> typical scanner land repeaters on a high hill, I get a hit with my pro 
> 83 just about 1 mile from the transmitter site with the unit in the cup 
> holder in the "stealth monitoring" vehicle.
> 
> Just wonder how small of a directional antenna one could one use with a 
> portable that would be effective but with a very small footprint.
> 
> Thanks to Tom (CT) from a message in the distant past, perhaps this 
> small directional antenna would be beneficial to "The Hunt" 
> http://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=LPY41 
> works for 400 to 1300 mhz BUT I would guess that even in the 162-174 mhz 
> it would work.....
> 
> Ken
> 
> 
> ----- Original Message ----- From: <JER1538A at aol.com>
> To: <fedcom at mailman.qth.net>
> Sent: Thursday, May 03, 2007 3:45 PM
> Subject: Re: [FedCom] air force base communications and encryption
> 
> 
>> MAYBE SOME DIRECTION FINDING IS IN ORDER     A FOX HUNT.....
> ..snip..snip...
> 
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