A friend of mine, K7HP, recently related to me some of his experiences
several years ago working on a large phased array of antennas for the
purpose of studying signal arrival angles in real time. That kind of
thing has always intrigued me, since that subject seems to be one of the
least understood and characterized among those affecting HF
propagation. Even the author of VOACAP, the de facto engine for most
amateur radio propagation software, has stated that optimum
takeoff/arrival angle (TANGLE) is by far the least dependable of all 20
parameters included in its predictions. K7HP indicated that some of the
data he saw showed significant changes in arrival angle within literally
fractions of a second.
So I was wondering ... if I mount two dipoles (non-resonant in order to
minimize coupling) at different heights on my tower and feed their
signals into my Elecraft K3 with its identical phase locked receivers,
is the relative phase angle of the two RF signals preserved in the
transition to audio? In other words, if the two antennas are receiving
the same RF carrier and the signal from the upper dipole leads the
signal from the lower dipole by 20 degrees due to arrival angle, and if
I tune both phase locked receivers to get a 1 KHz output, will those two
1 KHz tones have the same 20 degree relative phase difference? I
believe so based upon the existence of digital modes like PSK31, but
would like verification from someone who knows for sure.
If the phase angle is indeed preserved, I could feed both audio signals
into the X-Y inputs of an oscilloscope and watch the line rotate as the
arrival angle changed. Or I could record the audio to a stereo .wav
file and try to learn how to write an application that actually
calculated and tabulated the changes.
73,
Dave AB7E
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