I am not a Skimmer expert, and am just asking. Question: Are all the
Skimmers individually(and collectively) calibrated in concert? Can one rely
on them for comparing scientific data and conclusion to prove or ascertain a
point?Val>>>>
Val,
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.
The problems are:
1.) For determining small differences, less than around 5 dB, you have to
know the performance level of the reference antenna or station. (For that
reason, I use a simple dipole reference.)
2.) The reference and AUT (antenna under test) have to be reasonably close
together to eliminate propagation variances, but not so close as to
interact, and they have to be in the clear. For example, it would be foolish
for me to plant a dipole in the middle of a bunch of Yagi antennas and call
it a reference, or put the antenna being evaluated in an obstructed area.
3.) On skywave, there has to be some time involved with readings averaged
over time. This is somewhat true if there is more than a few wavelengths
distance between antennas, and especially true (almost critical) when
comparing different polarization antennas.
4.) Ideally the reference and AUT should be the same polarization, unless we
simply want to know which is louder overall.
5.) Antennas have sweet and sour heights for a given set of conditions. We
have to be very careful of this. This is especially true when antennas are
more than a half wavelength high above ground, because the antenna pattern
will be a series of deep nulls that selectively "notch out" a given wave
angle.
The RBN is an excellent tool. It does not need to be calibrated in absolute
level, only in dB, and dB to noise is just fine provided the noise level of
the receive site is steady.
One thing I hope we all can do is stop acting so "American" (we are now
what, 30th or 40th in math and science?) and get back to constructive
exchanges of information. If we stop learning and just pick a position and
fight, which is our trend today, this becomes a useless hobby and there is
no reason to communicate.
73 Tom
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