Need short range RDF antenna

[Jim]

I need some help in building a very short range antenna for use in
telemetry.

I do Box turtle research using 166mhz transmitters, and have gotten pretty
good at finding each turtle quickly even starting from a distance. I start
with a 3 element Yagi, and as I get closer, I use a passive attenuator with
bnc-bnc connectors for quick insertion between antenna and radio.

Using this simple equipment and lots of practice, I can easily pin down a
turtle within a couple feet of his location, then just search by eye.

What I would like is some sort of coil antenna or the like, that will
further pinpoint each turtle when they go underground for hibernation. Even
at 24 inch depth or so, I have still been successful at getting a good
signal and consequently, a location, but in this case, only with a 5 or 6
foot accuracy (as proved by there emergence holes in the spring).

I need to only work at this short distance, but be able to basicly point
accurately at the transmitter from 2 to 5 feet (soil depth plus air). I
used to work some in cave induction "radio" communications, which used good
sized wound coil receiver "antennas" placed flat on the ground above the
in-cave transmitter, and I know this problem is completely different, but I
envision I would like to do the same basic thing.

Any thoughts on what might work for me?

Thanks
Jim

[dave]

Post by Jim
I need some help in building a very short range antenna for use in
telemetry.
I do Box turtle research using 166mhz transmitters, and have gotten pretty
good at finding each turtle quickly even starting from a distance. I start
with a 3 element Yagi, and as I get closer, I use a passive attenuator with
bnc-bnc connectors for quick insertion between antenna and radio.
Using this simple equipment and lots of practice, I can easily pin down a
turtle within a couple feet of his location, then just search by eye.
What I would like is some sort of coil antenna or the like, that will
further pinpoint each turtle when they go underground for hibernation. Even
at 24 inch depth or so, I have still been successful at getting a good
signal and consequently, a location, but in this case, only with a 5 or 6
foot accuracy (as proved by there emergence holes in the spring).
I need to only work at this short distance, but be able to basicly point
accurately at the transmitter from 2 to 5 feet (soil depth plus air). I
used to work some in cave induction "radio" communications, which used good
sized wound coil receiver "antennas" placed flat on the ground above the
in-cave transmitter, and I know this problem is completely different, but I
envision I would like to do the same basic thing.
Any thoughts on what might work for me?
Thanks
Jim

The FCC says to use a 2 element Yagi (cardioid pattern) and aim the NULL
on the back of the antenna to pinpoint the antenna. I'll bet you won't
need the attenuator so much.

[dave]

Post by dave

Post by Jim
I need some help in building a very short range antenna for use in
telemetry.
I do Box turtle research using 166mhz transmitters, and have gotten pretty
good at finding each turtle quickly even starting from a distance. I start
with a 3 element Yagi, and as I get closer, I use a passive attenuator with
bnc-bnc connectors for quick insertion between antenna and radio.
Using this simple equipment and lots of practice, I can easily pin down a
turtle within a couple feet of his location, then just search by eye.
What I would like is some sort of coil antenna or the like, that will
further pinpoint each turtle when they go underground for
hibernation. Even
at 24 inch depth or so, I have still been successful at getting a good
signal and consequently, a location, but in this case, only with a 5 or 6
foot accuracy (as proved by there emergence holes in the spring).
I need to only work at this short distance, but be able to basicly point
accurately at the transmitter from 2 to 5 feet (soil depth plus air). I
used to work some in cave induction "radio" communications, which used good
sized wound coil receiver "antennas" placed flat on the ground above the
in-cave transmitter, and I know this problem is completely different, but I
envision I would like to do the same basic thing.
Any thoughts on what might work for me?
Thanks
Jim

The FCC says to use a 2 element Yagi (cardioid pattern) and aim the NULL
on the back of the antenna to pinpoint the antenna. I'll bet you won't
need the attenuator so much.

To pinpoint the turtle's transmitter...

[Jim]

The FCC? When did they get into instructing on receiving antennas? Of
course I know this method, but I will assure you that using an attenuator is
much more accurate than the null method, and MUCH faster. I have a 2
element Yagi for use on the same frequency, and it is inferior to the 3
element Yagi except that it is easier to carry folded in my pack. Both are
tape measure Yagi's.

......but do you have a possible antenna design solution to my stated
problem?

Thanks
Jim

Post by dave

Post by Jim
I need some help in building a very short range antenna for use in
telemetry.
I do Box turtle research using 166mhz transmitters, and have gotten pretty
good at finding each turtle quickly even starting from a distance. I start
with a 3 element Yagi, and as I get closer, I use a passive attenuator with
bnc-bnc connectors for quick insertion between antenna and radio.
Using this simple equipment and lots of practice, I can easily pin down a
turtle within a couple feet of his location, then just search by eye.
What I would like is some sort of coil antenna or the like, that will
further pinpoint each turtle when they go underground for hibernation.

Even

Post by dave

Post by Jim
at 24 inch depth or so, I have still been successful at getting a good
signal and consequently, a location, but in this case, only with a 5 or 6
foot accuracy (as proved by there emergence holes in the spring).
I need to only work at this short distance, but be able to basicly point
accurately at the transmitter from 2 to 5 feet (soil depth plus air). I
used to work some in cave induction "radio" communications, which used good
sized wound coil receiver "antennas" placed flat on the ground above the
in-cave transmitter, and I know this problem is completely different, but I
envision I would like to do the same basic thing.
Any thoughts on what might work for me?
Thanks
Jim

The FCC says to use a 2 element Yagi (cardioid pattern) and aim the NULL
on the back of the antenna to pinpoint the antenna. I'll bet you won't
need the attenuator so much.

[dave]

Post by Jim
The FCC? When did they get into instructing on receiving antennas? Of
course I know this method, but I will assure you that using an attenuator is
much more accurate than the null method, and MUCH faster. I have a 2
element Yagi for use on the same frequency, and it is inferior to the 3
element Yagi except that it is easier to carry folded in my pack. Both are
tape measure Yagi's.
......but do you have a possible antenna design solution to my stated
problem?
Thanks
Jim

All the way to the bottom:

http://www.qsl.net/wx9j/extrae9.html

No help with the underground issue. A couple feet of damp earth will
block a lot of VHF.