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SO-50 and AO-27



Yesterday I tried an experiment, to see how well (or poorly) I could copy
SO-50 with a half-wave whip (MFJ-1717) as compared with the Arrow, and also
with AO-27.

The results went like this: A long history of operating AO-27 with the whip
taught me that I need an elevation angle of at least 9 degrees to hear the
bird well enough to work it.  That corresponds to a slant range of about
2500 km.  My trials with SO-50 showed that I need an elevation angle of
approximately 30 degrees to get a comparable signal with the whip, and
approximately 10 degrees with the Arrow.  With the Arrow and AO-27, my
access was basically limited only by terrain, not by free-space path loss.
>From good locations, I've worked AO-27 down to 1-2 degrees using the Arrow.
At 30 degrees elevation, the slant range is about 1400 km.

AO-27 puts out about 500 mW, SO-50 about 140 mW, or so I'm told (haven't
checked the telemetry myself).  If those figures are correct, the difference
is about 5.5 dB.  Keith, W5IU, took an Arrow to the CSVHFS test range, and
it measured 10.5 dBd forward gain at 70 cm.  At 70 cm, the MFJ-1717 is
basically equivalent to a dipole.  Ground-reflection gain, properly used,
can add 5-6 dB to its performance, so my test results essentially conform to
theory: SO-50 is 5-6 dB weaker than AO-27, so SO-50 with an Arrow works
about as well as AO-27 with an MFJ-1717 plus ground gain.

In both cases, the downlink is the limiting factor, since my uplink power of
5 W is an order of magnitude stronger than either satellite's transmitter.
(The radio I used is an FT-50RD.)

73,

Ray


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