yes, this is a common problem. try checking out the arrl's radio direction
finding book for more specific techniques. but a couple simple ones are
1. a small loop, use the sharp nulls off the ends of the loop instead of the
big wide lobes.
2. a doppler system that electronically rotates antennas to give direction.
there is a very simple one on my web site at:
http://www.k1ttt.net/technote/doppler.html
3. a pair of phased verticals set up to give a cardioid pattern, again use
the sharp null not the fat lobe.

"Jim" wrote in message
...
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 wrote:
"What kind of antenna design could I switch to when I get to close range
that would have a narrower beam so I could pinpoint my target?"

J. Roy Smith, W6YA described what he called "the simplest of DF loops,
with no ambiguity of direction" in CQ magazine`s 1963 "Antenna Roundup".
Roy also called ot the "Nobaloop".

Roy said it was designed for locating signals on the 10-meter band but
has been used with reasonable success on the lower frequency bands. Roy
used the loop on 80 transmitter hunts winning first place 15 times when
many of his competitors were using identical loops.

The loop is about a 1-meter length of 1/4-in. dia.copper tubing (gas
line) bent into a neat circle. The two ends are flattened for about half
an inch in a plane perpendicular to the radius. Number 28 holes are
drilled through the flattened tubing about 1/4-inch from the ends. The
loop is attached to a coax receptacle such as Amphenol 83-IR or military
type SO 239. One loop end is attached to the outer conductor by a 6-32
screw through one of the four holes. The other loop end is placed over
the receptacle`s center conductor lug and soldered well.

The small loop gives a figure-8 response in the plane of the loop. The
attached coax distorts this pattern, adding its vertical response, like
a sense antenna. The resulting pattern is a cardiod.

Nearby vertical objects may need detuning to avoid interference with the
vertical loop.

The maximum lobe is about 30-degrees wide.

The null is about 5-degrees wide, according to the author.

I have not built it but it seems simple, small, and easy to duplicate.

Best regards, Richard Harrison, KB5WZI