Owen,

Thanks for the example. I do not have an impedance meter. I do have a vector
voltmeter that will read the phase and value of the reflected signal.

The core problem is: How to measure and improve the performance of a loaded
vertical. The unknowns are the value of ground and antenna resonance.

Setting the coax to a 1/4 wave multiple was a way to remove its phase altering
characteristics from the reflected signal at a frequency of interest. That seems
to be working and is predictable to measure the 1/4 wave odd, open circuit,
resonant points, etc. This simply proves consistent measurement and correct
identification of the electrical cable length.

I am pretty confident about the coax measurements at this time. Now on the to
antenna. I am not what the reflected angle is from the antenna. The coaxpair
program predicts it can vary 180 degrees for a purely resistive load.

Thanks for your help - Dan



Owen Duffy wrote:
On Wed, 28 Dec 2005 08:00:51 -0800, dansawyeror
wrote:



After making an error here between the effects of odd versus even quarter waves
at the source I am getting closer to being able to measure the impedance of a
loaded vertical 'in the shack'. At the moment this is limited to a single
frequency 'close' to a frequency of interest. But even that is a triumph.


Is that as hard as it looks?

Take an example:

You have an impedance meter to measure complex impedance at the
frequency of interest, being 3.6MHz for the sake of the example.

(This technique depends on the behaviour of the tranmission lines, you
would want to be sure that the transmission lines are in good
condition and work as characterised.)

You measure the impedance 40-j15 for example looking into a cascade of
5m of RG58 and 50m of 9913 connected to the unknown load.

The Z at the load end of the RG58 is 60.42-j20.13. That is the Z
looking into the 9913.

The Z at the load end of the 9913 is 41.94+j18.03.

Is this the kind of thing you are trying to do?

Bear in mind that you cannot know the characteristics of the lines etc
to support the precision shown above. You also need to keep in mind
the sensitivity of the results to changes in parameters to form a view
of the confidence limits of your measurements.

This took more time to write about than it did to find the results.

Owen
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