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May 8th 06, 06:07 PM posted to rec.radio.amateur.homebrew,sci.electronics.design

On 8 May 2006 09:01:51 -0700,
wrote:

Well I can understand how it might appear that way, but in truth I
certainly *do* read *all* the answers. Understanding them is another
thing, however. :-(

Okay. It's just that in an earlier post you asked, "What exactly is a
"through"?"

I said, among other things:

"A through is a direct connection of the two test ports (cables). If
all devices under test (DUTs) were "insertable", i.e. had one male and
one female connector (or GR or 7mm sexless connectors) then the test
port cables could be joined directly, thus forming a through ("thru")

Unfortunately, a lot of DUTs have the same sex connector on both
sides, thus a calibration thru must be a double, same sex adapter
(barrel). Using such an adapter during calibration adds some
unavoidable length (and loss and mismatch) to the test path length.
One method of removing (some of) the effects of the barrel is to
replace it after calibration with a matched length male-female adapter
that remains in the test path."

Now maybe I didn't make it clear enough, but if nothing else, I
inferred that extra length, even in an adapter, is a bad thing.

You then ask, "...The obvious question now is: in respect of throughs
and open and shorted terminations, is the coax length of these
relevant?..."

Sorry to have been short, but it appeared that you didn't read, or
believe anyway, my answer.

Unless you know otherwise, as you would with fully characterized
reference standards, the open-short-load-thru's are assumed to be
"perfect". A perfect short or open terminating a piece of coax,
regardless of length, is no longer "perfect". A non-zero length thru
isn't perfect either.

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