John S wrote in :

....

The manual for the Fluke generator says it is 50 ohms output Z. I used

Ok, be aware that sometimes that impedance is gauranteed to less than
full output.

If it is 50+j0, then your Vf reading should not change in magnitude with
load variation. If it does change, you have to factor it into the calcs
as in the AN.

your Line Loss Calculator to find that my 2.4m coax is 50-j0.1 and
0.671dB loss.

Since it seems you are applying the cal short at the load end of that
line section, then its loss is not so important (so long as it is
stable).


Nice numbers, but I don't know what to do with them.

....
The Fluke gen feeds the Narda dual directional coupler. The coupler
output has the 94 inches of RG-142B/U attached. The coax has all the
ferrite cores in my possession slipped onto it to moderate common mode
current. The vector voltmeter A input is attached to the forward
coupler sampling port and the voltmeter B input is attached to the
reverse coupler sampling port.

I put the best short circuit I can muster on the far end of the coax
and set the vector voltmeter to read 180 degrees. I record the A and B
voltage inputs.

Ok, that sounds fine. If find it helps to measure something that is
known. Do you have a pair of 50 ohm terms and a T that you can measure
and convince yourself that it is working.


I put the antenna on the far end of the coax. I read the A and B
voltages and the angle between them. I use Excel to calculate the
results as indicated in the HP AN-77 app note.

Sounds fine.


I am aware of the common mode current problems and I do everything I
can to minimize them. I don't know if I am successful, but I test the
effectiveness of my efforts by running my hand up and down the coax
and watching the voltmeter. I haven't been able to get all variation
out, but some of the variation is due to my hand proximity to the
antenna itself.

Ok, but it remains a potential problem.

Owen