On Tue, 15 Nov 2005 15:38:28 -0700, Tod wrote:
>Those values look like they are within about 2% of expected values for the R
>and within 20% or so on the X. Is the analyzer accuracy any better than that
>if there is NO coax between the load and the analyzer?
What Jim Lux has shown by cranking the numbers is that when the VSWR is small,
the effect of the transmission line is small. That would be true whether the
line was a half wave or not. But when it's a half wave length, it has almost
the effect of moving the analyzer to the antenna terminals AT THAT FREQUENCY.
I say "almost" because the loss in the line will reduce the VSWR slightly (but
VERY little on topband).
Tom can tell you a lot more about analyzer errors. But consider this -- it
isn't really possible to stick the analyzer at the antenna and read it without
a very tall ladder, and your presence next to the analyzer will detune it a
bit. There's also the interaction of the antenna with the coax. Other errors
-- the analyzer has some finite input R and C. For small VSWR, neither mean
much, especially at 2 MHz, but they sure do at higher frequencies and high
VSWR. As I recall, W4EF said that the AEA CIA-HF has input Z on the order of
10-12K in parallel with 12 pF. That's an older box, and the new one may or may
not be better.
Jim K9YC
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