K4XS wrote:
>What exactly does swing wildly mean? On a frequency range from 1.8-7.0 what
should one expect? My situation is a little different in that I use 75 ohm
hardline buried to the beverages and use the MFJ 259 which is designed for 50
ohms. Most of the band from 1.8 to 7.0 measures around close to 1:1 to around
2:1 which I assume is not too bad.
Bill, I'm not sure what you are measuring at the
end of your 75 ohm feedline using a 50 ohm analyzer. I
use 75 ohm feedlines also, but this is how I use 50 ohm
analyzers to check my Beverages (without adding the
complexity of measuring at the end of a mismatched
coax):
1. I made a portable transformer for my analyzers with
wing-nut connectors for the Beverage hot and ground wires.
This transformer is matched for 50 ohms which matches both
my MFJ and AEA CIA-HF (which is great for swept measurements).
2. I adjust termination R for a flat swept response. You
can see a swept display of the HF-CIA from 1.5-6.5 MHz in the
talk I referenced previously (slide #16). That one varies
from about 1.2-1.4 over the range. I have some that are
better and some that are worse, but 1.0-2.0 would cause me
to keep working on it (when measured without any 75/50 ohm
measurement issues). Some of my worst are about 1.2-1.8,
but they are generally in non-critical directions and on my
"when I get around to it" list for the future.
3. Once the response looks good at the Beverage itself, I
then connect my 75 ohm coax using a permanent transformer,
which is also matched to 75 ohms. If I suspect problems, I
never check at the end of the coax but at the feed point
directly as in #2.
4. BTW, one advantage of the Autek VA-1 is that you can
set its measurement impedance to any of several common
feedline impedances (e.g. 50, 75, 93, etc). This would
avoid the 50/75 measurement issues mentioned above.
73, Bill W4ZV
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