[amsat-bb] AO-73 telemetry reception

Patrick STODDARD (WD9EWK/VA7EWK) amsat-bb at wd9ewk.net
Sun Mar 29 19:50:22 UTC 2015


Thanks for the SO-50 contact last night. Nice to finally work you!  I read
this e-mail last night when I was still on the road, but wanted to wait until
I was back home - and awake - to scribble a response.

There is a difference between hearing the AO-73 telemetry and actually
copying data from it, especially when it is in the low-power (30mW) mode.
As ON4HF mentioned earlier, it can be tough. With AMSAT-UK trying to
keep the transponder active throughout the weekends, the times you
would be able to hear the high-power (300mW) telemetry would be
weekday mornings. If you're not able to be at home, maybe you could
set up your station to do that automatically.

With the high-power mode, I can regularly copy 60 to 80 packets when
using my Elk log periodic and FUNcube Dongle Pro+ in my back yard.
Using AMSAT-UK's VHF crossed dipole instead of the Elk, that number
easily goes to 100 or more on all but the most shallow of passes. At low
power, no matter which antenna I use, I have never copied more than 10
packets on any pass - even when I can clearly hear the signal. ON4HF
mentioned his antenna, which is a bit larger than my Elk, and the lower
signal strength he observes.

When the beacon is in low-power mode, I think a directional antenna is
a must. A 5/8-wave ground plane is not optimized for satellite work. Even
a simple 1/4-wave ground plane might work better than the 5/8-wave, but
the 30mW beacon would still be tough to get enough to decode. A preamp
may also help, along with higher-quality coax. If you have a chance, try
copying the telemetry on a weekday morning when it is on at higher power,
to see the difference.

The ISS is not necessarily a good example to judge how your station copies
signals from space. Its transmitters usually operate at anywhere between 5
and 25 watts, compared to lower power levels used by AO-73's beacon, or
satellites like SO-50 (250mW). With the higher power level, the ISS can be
heard on omnidirectional antennas that would probably be


Twitter: @WD9EWK

On Sat, Mar 28, 2015 at 10:45 PM, Steve Kristoff <skristof at etczone.com> wrote:
> I would like to receive the telemetry from AO-73. I have the FUN-Cube Dashboard running. I can hear the telemetry signal on my Yaesu FT290RII set on USB and run through a Signalink USB to my computer. The antenna is a 5/8 wave ground plane on top of my 2 story house.
> I can get ground based APRS. I can receive ISS APRS and packet. Occasionally I can even hit AO-07 in mode A.
> I have received the AO-73 telemetry once, but nothing since.
> Do I need to use a directional antenna? Maybe it's because I'm only home at night and weekends and the telemetry is at 30 mW during those times? Would a pre-amp help?
> All helpful thoughts and ideas are very welcome!
> Steve Kristoff AI9IN
> EM79ji
> Oldenburg IN
> skristof at etczone.com

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