[amsat-bb] Antenna better when NOT pointing directly at TX source?

Andrew Glasbrenner glasbrenner at mindspring.com
Thu Mar 9 00:28:12 UTC 2017

I recall in the Mode K and A days, yagis tuned for the low end of 10m would often display very skewed patterns on 29.4 MHz.

Given your antenna is presumably tuned/designed for 435, it's pattern at 400 is likely very different.

Also, 45 degrees seems excessive for satellites unless you live in a hole, and certainly for balloons close to the horizon. I'd try 15-20 degrees.

73, Drew KO4MA

> On Mar 8, 2017, at 7:09 PM, Scott <scott23192 at gmail.com> wrote:
> Hello everyone.
> 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
> as well.
> 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
> antenna.
> 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?
> Thanks!
> -Scott,  K4KDR
> Montpelier, VA  USA
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