I have about 94 inches of RG-142B/U. I am using a Fluke 6061A signal
generator, an HP 8405A Vector Voltmeter, and a Narda dual directional
coupler. I have tried to measure the line characteristics at 434 MHz but
I am not satisfied that the results are accurate. It is very difficult
to get good short and open circuits at this frequency and I also wonder
if the 8405A accuracy suffers since a short is well away from the
nominal system impedance of 50 ohms.

What if I simply calibrate the 8405 with a short on the end of the line
(the measurement plane) then attach my antenna and accept the readings?
Will they be very far from the real value?

Thanks,
John KD5YI