I just took some cable loss measurements with my AEA CIA HF Analyst and got
some odd results. The net one-way losses for my 260-foot run of LMR0400UF
are:
Frequency Measured Computed
Loss Loss
3.750 MHz .95 dB .70 dB
7.150 1.65 1.00
14.150 1.85 1.40
21.225 1.60 1.70
28.250 2.20 2.00
As you can see, the measurements for 80M, 15M and 10M are quite close to the
computed losses, and the differences could easily be accounted for by the 8
PL-259's and one set of relay contacts in the run. But the measurements for
40M and 20M are significantly higher than the computed values. The antenna
SWR curves, as measured from both the CIA HF and the transceiver are normal.
Does anyone know what might be causing the discrepancy? Could it be
broadcast interference? I've heard about that happening to these analyzers
on 7.0 MHz and I've had odd readings at this QTH on 40M antennas and phasing
lines with the AEA, MFJ and Autek analyzers. Never had problems at 20M,
though. It is interesting that the discrepancy on 20M is half that on 40M.
Does that imply an interfering signal that drops to about half power at the
first harmonic? There's an AM station about 6 miles from here (1340 KHz),
but I believe they run low power. Could that be the problem? Why doesn't it
show up on 80M, too?
Any light would be appreciated. Thanks.
73, Dick, WC1M
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|