Hi Tony,
Thanks for making the recording of aircraft reflections. Yes, we also
see and hear aircraft reflections mixed with atmospheric disturbances
all the time. The aircraft reflections sound similar to what you hear on
the beacon, and you can identify those because they vary in frequency
and intensity as the airplane approaches or recedes, just like you hear.
However, what we experience on UHF over longer paths is a constant
"chopping" up of the SSB phone signal, or narrow digital signals, and
that seems to correlate with the Hepburn propagation maps, especially
when the path crosses two or more levels of ducting, when signals can be
strong, but SSB is still not very understandable. When both stations are
within the same ducting level, the only audible Doppler effect is
usually reflections from airplanes, and sounds much like your recording.
When there is no propagation enhancement showing on the Hepburn maps,
there is usually a fast, constant, "chopping up" of the SSB phone
signal, and when we switch to a relatively wide digital mode, like
Olivia or Contestia, which continues to print for a couple of seconds
after transmission has ceased (due to the interleaving and FEC, I guess)
print is perfect. The frequency of the audible chop is generally around
two to three times per second, which is less than the latency of the
digital mode. Those modes which display very little or no latency seem
to be the ones that fail to print.
Over the next few weeks, we are now going to compare Contestia
variations with different bandwidths and latency to see how print
compares to the observed period of "chop" on SSB phone.
73 - Skip KH6TY
