Determining antenna resonance with a grid dip meter
 

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

The length of the driving element is not critical and may not resonate by
itsself depending on the matching device used.

W5DXP wrote:
Tom Coates wrote:

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?


Usually a couple of loops of coil are fastened to the end of the
transmission
line and the grid dip coil is inserted into the loops. Seems I had more fun
with that old grid dip meter than I now do with an antenna analyzer. It
contains
a 6C4 and still works.

I have an AN/PRM-10 GDO and I will not part with it.

I have a MFJ 259B and I will not part with it, either.

Follow the instructions above with a GDO. For more detailed analysis the
MFJ 259B or equivalent Analyzer will do a FB job.

Deacon Dave, W1MCE

Tom I don't have an answer for you.

I came across your message because I tried to use the MFJ Antenna Analyzer
to tune a 20 meter quad, and could not figure out how to get the "grid dip"
function to work.

So I will follow your thread with interest.

Terry - W6LMJ

On 8/26/03 10:00 AM, in article , "Tom
Coates" wrote:

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 ...
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

Terrence R. Redding Ph.D. wrote:
Tom I don't have an answer for you.

I came across your message because I tried to use the MFJ Antenna Analyzer
to tune a 20 meter quad, and could not figure out how to get the "grid dip"
function to work.

So I will follow your thread with interest.

Terry - W6LMJ


Terry, If you use the MFJ 259B version you can go to Advanced Mode by
depressing 'Gate' and 'Mode' simultaneously. Press the 'Mode' switch to
cycle through the options. Select 'Resonance' Mode. You now can sweep
across your system, starting at the lowest frequency range [1.8 MHz] and
determine resonance at the Zero reactance frequency. Be advised, that
the load may not be 50 ohms though!!

Deacon Dave, W1MCE

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