"Owen Duffy" wrote in message
...
On Thu, 29 Dec 2005 00:53:44 -0700, Wes Stewart
wrote:


You're making this way too complex (pun intended).. Why not just
connect the coax to the bridge and put your open-short-load standards
on the far end and do the calibration?

Or move the instrument out in the field?

Wes, I have been guessing that Dan wants to measure the antenna over a
band of frequencies, and doesn't want to be popping up to the
feedpoint for every frequency cal.

No doubt, the process you propose Wes is simpler and more accurate, if
it is physically convenient.

Would calibration against a single s/c standard be accurate enough for
the purpose at hand. Perhaps a coax relay at the antenna feedpoint to
switch between a s/c port and the real load might be accurate enough
for calibration, and a whole lot more convenient. IIRC there is only
around 0.4dB of line loss from the shack (ie the desired VVM location)
to the feedpoint.

Dan, I think you have gotten on a sidetrack about building the
transmission line out to a tuned length. It is not necessary, or even
desirable as far as I can see, but it has the downside of complicating
the calcs and increasing scope for errors when you build out with a
different line type.

Owen

Wes, and Owen, This problem of how to resolve the terminating impedance
seems so simple that I realize that I (again) must be missing something.
Wouldnt it be accurate enough for Dan to record the impedance at his coupler
for two conditions, 1) short circuit at the antenna end of the coax, and 2)
the antenna connected. Plot both impedances on a Smith Chart. Since the
impedance associated with the short is known to be zero, he needs only to
rotate *both* impedances thru the same angle needed to place the short ckt
impedance at zero on the smith Chart.

Jerry