Mike Dower is right about the antenna pattern and impedance
characteristics varying with frequency. An HF communications system
can use the whole 2-30MHz band, over which the antenna characteristics
can change dramatically. The gain of a resistively loaded manpack
antenna can range from -20dBi to 5dBi from 2 to 30 MHz repsectively.
However, the propagation characteristics are likely to change by at
least as much over the same frequency range. The ionospheric
propagation loss will also change with time, even at a fixed
frequency. The net result is a change in carrier level at the receiver
input which should be taken care of by the AGC, unless of course, the
level falls below the receiver threshold.
Regards,
Paul Carlier
Received on Tue Feb 15 2000 - 21:50:39 EST
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