Thanks,

I went back through the calibration procedure.

1. The meter appears to be performing as it is supposed to. The 'static readings
work repeatably and predictably. With a balanced configuration shorts and
opens read correctly.

2. The pad I was using appears to have a frequency shift. With the 'legs
balanced for length' the measurement would change with frequency. This really
confused the measurement process. I put it aside.

3. I have some 23 Ohm couplers. These of course confuse readings when used as
normal couplers. However if they are used in a truly balanced configuration -
that is the legs are configured as close to identical as possible then they
appear to work.

I am going to shelve this until I find or make a 50 Ohm bi-directional coupler.

Thanks again - Dan


Owen Duffy wrote:
On Mon, 02 Jan 2006 16:10:02 -0800, dansawyeror
wrote:


The coupler measures
about -14 dbm.


What does this mean? Are you trying to tell us that the power on the
coupler port is 14dB less than the through power? What has dBm got to
do with it?

You didn't report the power in the coupler port with a s/c and / or
o/c at the measurement plane. Did you perform this cal?


(The phase angle and reflected ware very touchy. It was almost impossible to
adjust by changing frequency. It was easier to 'adjust' it by sitting very still
and moving my arm.)


That is understandable. How much coax between the A probe and the
load, and the B probe and the load... how many degress does this total
electrical length change for a 1% change in frequency? Does that
explain some of the phase sensitivity?


The antenna is a copy from the ARRL handbook. It is a 4 inch segment, a 1 inch
long by 3/4 inch diameter 5 turn coil, and a 4 inch tip. It is mounted over a 2
foot square aluminum plate. This antenna should have an input impedance less
then 20 Ohms.


Don't you need to measure some "known" loads. Why not try a 50 ohm
load tee'd to a s/c stub (quarter wave at a known frequency) and see
if you get the predictable results at different frequencies around
resonance. Then try two 50 ohm loads in parallel with the stub. (339mm
of RG58C/U should have a Z of around 6000+j0 ohms at around 146MHz, at
half that frequency it should be 0.85+j50, etc...


How can it measure very close to 50 Ohms? Is there something wrong with this
analysis?


See if you can trust your measurements on known loads before wondering
why the unknown load isn't what you expect when using unknown
measurement technology... too many unknowns.

Owen
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