Jim wrote:
This isn't strictly a Ham question, but I hope you all can help me anyway.

I am using small transmitters in the 166-167 mhz range in some Box Turtle
research I am doing. My RDF antenna is a 3 element Yagi designed via
Yagicad 4.1 which works pretty well. It has 48db front/back and about 90
degrees beamwidth in the H pattern.

This works well for initial locating......usually starting 1500 to 2000 feet
from my transmitter, but the closer I get, the more inaccurate it becomes.

What kind of antenna design could I switch to when I get to close range that
would have a narrower beam so I could pinpint my target? It would be nice
to have something smaller than my 35" x 21" yagi for close in work, but the
beam width is the primary concern.

Yagicad doesn't let me design solely on beam width (at least I haven't
figured out how) so is there another way to go on this??

Thanks
Jim



Jim,

Assuming your transmitters are NOT super well filtered I would build a
yagi for 3 times the frequency (498-501MHz) and listen on that frequency
when very close. Very few transmitters will be so clean as to not be
able to hear the 3rd harmonic. I DF and do running ARDF very often and
if you don't mind the small second antenna and you have a receiver that
can tune to the 3rd harmonic this will get you both the needed
attenuation for being close and the ability to pinpoint the source.

73,
Larry, W0QE