Try http://w1.859.telia.com/~u85920178/use/gdo.htm

BR from Ivan

"Tom Coates" wrote in message ...
I recall reading about this many years ago but can't find it in any of the
books I have now.

How do I couple the meter to the antenna?

The project is a 3-element 2 meter yagi and I'm trying to set the length of
the driven element. I can't find a dip within the band using the rig and an
swr bridge.

Tom, N3IJ

Try http://w1.859.telia.com/~u85920178/use/gdo.htm

BR from Ivan

"Tom Coates" wrote in message
...

How do I couple the meter to the antenna?

Tom, N3

Ivan & Tom-

I've had a couple of old Heath GDOs over the years. I was never able to find a
dip by coupling into the antenna's co-ax. I see that Ivan's article above
contains the "secret" method I finally found that works - you have to
short-circuit the feedpoint of the antenna and couple directly to the element.

The article above suggests that you can form a loop in the antenna wire to
couple more tightly to the GDO. However, that would tend to introduce
inductance which would interfere with the measurement. What I do is lay the
coil next to the antenna element so the antenna wire is parallel with the GDO
coil wire tangent.

For example, take a one meter wire or un-bent coat hanger. A GDO coupled to it
should have a dip at 150 MHz. I expect there will also be a dip around 450
MHz, et cetera (odd harmonics).

73, Fred, K4DII

What I always did, and I'm sure it was in the manual, was to wind a
few turns of hook-up wire and solder the ends to a coax connector. I
then plugged in the coil at the end of the coax, stuck the GDO coil
through the coil on the connector, and took a reading. I can't recall
that using that method ever mislead me. I think I even have that
little coil on a BNC out in the junkbox.

I sold the Eico GDO that I had for years. In 1999 I acquired a Millen
GDO in mint condition from an estate sale. I sold it on Ebay, but now
wish I had kept it.

Dick - W6CCD

On 31 Aug 2003 16:48:47 GMT, (Fred McKenzie) wrote:


Try http://w1.859.telia.com/~u85920178/use/gdo.htm

BR from Ivan

"Tom Coates" wrote in message
...

How do I couple the meter to the antenna?

Tom, N3

Ivan & Tom-

I've had a couple of old Heath GDOs over the years. I was never able to find a
dip by coupling into the antenna's co-ax. I see that Ivan's article above
contains the "secret" method I finally found that works - you have to
short-circuit the feedpoint of the antenna and couple directly to the element.

The article above suggests that you can form a loop in the antenna wire to
couple more tightly to the GDO. However, that would tend to introduce
inductance which would interfere with the measurement. What I do is lay the
coil next to the antenna element so the antenna wire is parallel with the GDO
coil wire tangent.

For example, take a one meter wire or un-bent coat hanger. A GDO coupled to it
should have a dip at 150 MHz. I expect there will also be a dip around 450
MHz, et cetera (odd harmonics).

73, Fred, K4DII

Of course, the two basic methods of coupling a grid dipper to an antenna are
capacative and inductive. For capacative, couple one side of the dipper coil
to the end of the antenna by 2 to 5 pf. You may be changing the resonant
frequency by stray coupling.
For inductive, make a coil shaped like a wire coathanger, size or more than
one turn to get to the right frequency. couple the long side of this "coil"
to the center of the element.
bob w4mb

Of course, the two basic methods of coupling a grid dipper to an antenna are
capacative and inductive. For capacative, couple one side of the dipper coil
to the end of the antenna by 2 to 5 pf. You may be changing the resonant
frequency by stray coupling.
For inductive, make a coil shaped like a wire coathanger, size or more than
one turn to get to the right frequency. couple the long side of this "coil"
to the center of the element.
bob w4mb