John S Inscribed thus:

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

The easiest way to get the characteristics of the line is to look up the
manufacturers data. Somehow I don't think that this is really what you
are looking for !

Irrespective of line length if its terminated in its characteristic
impedance then you will only measure unity vswr. Open or short circuit
terminations are easy enough to obtain. Having a known input quantity
and measuring the return value will give you the line loss for that
particular line length.

I suspect that its actually the antenna characteristics that you are
seeking to measure ! In which case I would use a line, accurately cut,
to be number of half waves long, then the impedance presented at the
far end would be repeated at the near end. Of course you would need to
have an accurately cut quarter wave length in order to determine
whether the load was inductive or capacitive in nature.

I'm sure that if I'm mistaken some of the more knowledgeable will
correct my errors.

HTH
--
Best Regards:
Baron.