On 1/29/2013 9:46 AM, Paul DeWitte wrote:
I just hooked the same coax to each rig, so it was a few seconds
between each one. He was not always solid copy on the Omni VII, but
was Q5 on the Corsair II.
Several thoughts.
First, I've spent a LOT of time trying to evaluate the differences
between antennas that are predicted by NEC models to have definite, but
small (3-6 dB) differences in their directivity. My station is set up so
that I can switch instantaneously back and forth, but even with that
ability, signal fading often overwhelms the differences in the antennas.
The same thing could be affecting your evaluations. 160M has a LOT of
QSB, the peaks can be strong, the dips can be deep, and can coincide
with the switching. I've seen exactly this effect watching reverse
beacons using JT65 on 160M to the east coast from California, and
switching between two antennas on alternate transmissions. If one
antenna coincides with the timing of QSB peaks it looks better, but a
difference in that timing can make the other one look better.
Second, the setup of the radio can have a very strong effect on our
ability to copy a signal. Is the preamp on? Is anything getting
overloaded? What roofing filters? What IF bandwidth? What audio
filtering?
To do tests like what you want to accomplish, a switching system is
required that simultaneously switches the antenna from one rig to
another t the same time that headphones are also switched. And this sort
of test MUST be done with headphones -- differences in how speakers in
radios interact with the acoustic environment in the room, whether those
speakers are partly blocked by equipment stacked on top, etc. can affect
how well we copy a signal.
73, Jim K9YC
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