On Mon,8/18/2014 4:53 AM, Tom W8JI wrote:
A live comparison of S/N ratio or relative level over time is with
very few exceptions an excellent comparative test. It is much more
accurate than S meters or absolute levels without a comparison
reference. As such, the RBN is a great tool for evaluating systems.
Yes. BUT -- my experience has been that I must average hundreds of data
points to get meaningful data. The reasons are simple -- we must contend
with QSB, and as Tom noted in another post, nulls in the patterns of
antennas at both ends. A few years ago, I tried to compare two 160M
antennas using JT65 and W6CQZ's JT65 RBN. On a good night, I would see
reports from 3-4 stations east of the Mississippi. I alternated between
the two antennas for hours, putting the reports in a spreadsheet, and
studying the data. Modelling predicted differences of a few dB, and I
never found that the data was good enough to confirm the models. The
antennas are passive arrays of fairly tall verticals of a quarter wave
or less, so there are no vertical nulls in their pattern. I can clearly
hear their directivity on RX, but their gain is what I was trying to
confirm.
73, Jim K9YC
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