[amsat-bb] Antenna better when NOT pointing directly at TX source?
scott23192 at gmail.com
Thu Mar 9 00:09:42 UTC 2017
While my question is not directly satellite related, I hope that it's a
general antenna question that might be of benefit for satellite reception
I have developed an interest in tracking the 400 MHz radiosonde
transmitters used by the (U.S.) National Weather Service office on the
other side of the state for their twice-daily weather balloon launches.
When the wind carries one anywhere in my general direction, it's a lot of
fun to try to receive & decode the position & altitude telemetry being sent
by the thing. Maybe one day I'll even hit the road and track one down!
Anyway, my question is in regard to the pointing of my antenna, which is a
70cm X-Quad connected for RHCP. The elevation is fixed at 45°.
I have confirmed that my antenna is pointing in the compass direction
indicated by the indoor control box. The radiosonde is telling me via
telemetry what its location is. From that, it's easy enough to plot on
Google Earth and see exactly what the compass heading is from my location
to the balloon at any given time.
The catch, even considering the ~ 10° declination at my location, is that
it's very common for me to receive a MUCH stronger signal with my antenna
pointing 45 or 90 degrees away from what should be the correct heading! I
sweep back and forth and it varies... and also depends on how close the
balloon is to my location. But for much of a flight, especially at greater
distance, it's quite common to receive a huge signal off-heading... where
if I point directly at the transmitter, it's barely out of the noise.
I don't know if this is a polarity issue, an issue caused by the
transmitter wildly swinging around under the balloon (much like a tumbling
satellite?), or an issue caused by the characteristics of my particular
So that's my dilemma; I can't tell you anything about the TX side because
for this particular aspect of the hobby, I'm only concerned with
reception. But is there any legitimate reason for me to be seeing these
massive differences in receive SNR when I am turned so far away from the
transmit source? Anyone ever seen this in other situations?
Montpelier, VA USA
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