I recently replaced my two main 190-foot feedlines to the tower with
LDF4-50A hardline. On the shack end, there is about 50 feet of fairly old
RG-213 (12 years or so). Today I used my 259B to measure the combined loss
at 30 MHz, with the far end open-circuited. I got 1.3 dB on one cable and
1.4 on the other, which correlates very nicely with the rated attenuation
of the cables. However, there was one strange thing - strange to me,
anyway. with the 259B in coax loss mode, I found that relatively small
frequency excursions would cause a relatively large change in the reported
loss - going, for example, from 1.3 dB at 30 MHz to 1.6 at 29.6 MHz - and
of course, if anything, you'd expect the attenuation to go down with
decreasiong frequency. The variation in reported loss is also cyclical as
I tune further down.
The manual for the 259B doesn't say anything about this sort of frequency
sensitivity, but I remember that with my old Autek it was necessary to tune
for minimum R and then apply a formula to determine loss. Is this just an
omission in the MFJ manual, or something I don't understand, or maybe a
problem with the unit itself?
73, Pete N4ZR
The World HF Contest Station Database
Full details on 3300 contest stations
Updated 5/5/07 http://www.pvrc.org/WCSD/WCSDsearch.htm
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