[amsat-bb] Antenna better when NOT pointing directly at TX source?
normanlizeth at gmail.com
Thu Mar 9 04:02:42 UTC 2017
The receiver is overloaded pointing near the source (and the rx
target). Farther to the side of the pattern, the signal to noise seen
by the receiver is better.
I set up 9 times in Suriname for mode B. Heard the satellite 3 times,
myself twice. Some interference on UHF, just enough to make 3 degrees
was my horizon. El sucko if you're trying to bag EU on FO-29.
Spent most of my free ish time troubleshooting this.
First checked the VHF cavity I brought. It was OK. Then the cables.
Then the antenna. Then swapped radios. Then tried something weird:
Normally the gear looks like this:
With nothing to lose, I tried setting the VHF antennas up like this.
The UHF antenna was, of course pointing downrange.
The antenna pattern went from cardoid to cloverleaf. DEEP nulls at the
sides. Found an RFI source in 5 minutes. Heard AO-7 mode B clearly
for most of the pass I set up for. EXCEPT where the antenna was
capturing more noise than signal.
There was an RFI source within 100' that was broadband and s9+. Point
away? Hear satellite. Point in the direction of the noise? Nothing.
The noise went down to 29MHz. Tried AO-7 mode A. Could hear the beacon
off of the rear corners of the Mosley at 90'.
Of course it was time to leave.
Will attempt activation again in the fall.
pz5yk (or n3ykf) or Norm
On Wed, Mar 8, 2017 at 7:28 PM, Andrew Glasbrenner
<glasbrenner at mindspring.com> wrote:
> 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
>> 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?
>> -Scott, K4KDR
>> Montpelier, VA USA
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> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
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> Not an AMSAT-NA member? Join now to support the amateur satellite program!
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