On Thu, 29 Dec 2005 10:15:50 GMT, Owen Duffy wrote:

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.

I've provided a spreadsheet that facilitates the calculations over a
range of frequencies.

www.qsl.net/n7ws/8405.zip

So a couple of trips to the end of the cable are all that are required
to calibrate the setup.

(I must confess, I haven't tried this program with a line much over a
few inches in length to determine whether my calibration functions can
handle it, but I think so.)

Without doubt, the chance of errors creeping in using a long cable is
increased, but the alternative of trying to "calibrate" a cable and
subtract its effects mathematically is equally suspect. In fact, the
one-step process is pretty much the same thing; the cable is being
characterized by the calibration process.




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