On Tue, 11 Oct 2005 01:03:34 -0400, "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


You already got two good suggestions from others. Here's a third.
Build a MOXON square, less gain than yagi but if built right the MOXON
has a very distinct readward null, you exploit the null. Another
small advantage is it's smaller than a 2 element yagi for the same
band.

Allison

wrote in message
...
On Tue, 11 Oct 2005 01:03:34 -0400, "Jim" wrote:

...
You already got two good suggestions from others. Here's a third.
Build a MOXON square, less gain than yagi but if built right the MOXON
has a very distinct readward null, you exploit the null. Another
small advantage is it's smaller than a 2 element yagi for the same
band.

Allison
Look up the "Tape Measure Yagi" It is designed to have a null off the back,
but you'll have to adjust the center freq.
73, Steve, K,9.D.C'I

On Wed, 12 Oct 2005 15:11:29 -0500, "Steve Nosko"
wrote:


wrote in message
.. .
On Tue, 11 Oct 2005 01:03:34 -0400, "Jim" wrote:

...
You already got two good suggestions from others. Here's a third.
Build a MOXON square, less gain than yagi but if built right the MOXON
has a very distinct readward null, you exploit the null. Another
small advantage is it's smaller than a 2 element yagi for the same
band.

Allison
Look up the "Tape Measure Yagi" It is designed to have a null off the back,
but you'll have to adjust the center freq.
73, Steve, K,9.D.C'I

I've built both. The Tape measure yagi is not nearly as good off the
back and a bit larger. Moxon well done is an easy 35+ db null off
the back and sharper.



Allison