Bob Bob wrote in
:

Hi Jim

Hams will quite often get involved in hidden transmitter hunts during
field day games. You might be surprised at the expertise out there.

Some notes/thoughts for you;


- I'd suspect that the problem might actually be more in the receiver
than antenna. As the signal gets stronger/closer the radio might be
running out of signal reporting range,. ie everything is just over a
certain value so it is treated as being at maximum. It is quite common
under these conditions to switch in an amount of attenuation to reduce
the signal to a more reportable figure. This usaully goes in the
antenna feedline.

- In addition to the above your receiver may not be very well shielded
such that signal actually bypasses the antenna/coax path and thus
gives you less peaks and nulls to go off. You can check this by
placing a dummy load (usually 50 ohms) in the antenna cable socket and
checking for the nearby signal.

Ahhh, you beat me to this.

Now, if the receiver IS well shielded enough, if you can insert a
switchable attenuator in the coax, you can reduce the signal strength
significantly...and, FM receivers get very non-linear below about 20dB
quieting, they quiet faster than the actual input. In otherwords, you
could get 3-4 dB quieting change for 1dB of singal change. What this will
do is make you antenna pattern SEEM narrower.

What I used to do was to change to an RF field strengtth meter with a
small cavity filter tuned to the frequency I was hunting when I got
really close.


- The human body is excellent for using as a directional attenuator.
If you had a simple omni antenna attached and only a few inches in
front of your body you'll get maximum attenuation (lowest signal) when
you are facing away from the target turtle.

YES! But, you need to keep you body completely symetrical, stick an elbow
out and you will distort the pattern. Also, when the signal gets large
enough, remove the antenna.


-Bruce