[amsat-bb] FUNcube telemetry performance?

Mark Spencer wa8sme at comcast.net
Sat Apr 19 15:17:32 PDT 2014



I have been monitoring the FC telemetry pretty closely and have some
observations for what it is worth:


1.        The last update to the Dashboard produced marked improvement in
decoding the telemetry.

2.        Using an IC910, M^2 14-element RHCP yagi with antenna mounted
preamp, I typically decode around 120 frames and lose around 10 frames.

3.        Using the FCD with a simple turn-style RHCP with antenna mounted
preamp, I will get approximately one third the performance of the main
station setup.  Using a simple antenna with no preamp I get dismal
performance with the FCD.

4.        Of course I have more success decoding the telemetry when the bird
is in the daylight mode than when operating in the night/transponder mode.

5.        I have not noticed any significant fading of the signal with the
M^2 setup except some minor fading at AOS/LOS.  I will get fading using the
turn-style however the fades appear to be due to the nulls in that antenna
pattern more than due to fades from the satellite.  However, the reduced
signal strength helps to emphasize the fades with the turn-style.

6.        I estimate that it takes a minimum of 50 decoded frames to capture
a full set of whole orbit data.  It requires a significant number of
additional frames to capture usable high resolution data during a pass (I
define a usable data set as being able to determine the rotation rate of the
satellite from the high resolution data).

7.        There is significant frequency drift in the downlink frequency
that tracks the temperature of the satellite internals.  I also notice
significant FMing of the downlink frequency when the transponder is being
used (appears to track with the power used by the transponder).  The
Dashboard does a pretty good job of compensating for these frequency
deviations, I haven't noticed any significant loss of data due to this
FMing.  The frequency drifting needs some attention when using a traditional
rig under computer control (the drift is beyond Doppler).  When using the
FCD, the Dashboard takes care of the temperature drift issue.


One of the many interesting things that I am monitoring on this bird is the
rotation rate.  The bird started out with a rotation rate of .4 RPM, then
something happened on or about December 28th and the rotation abruptly
started to slow down to a minimum rate of .12 RPM (or 8.5 minutes per
revolution) around the end of January, then it started to spool up again to
a maximum rate of 1.16 RPM around the end of March, and then it started
slowing down again.today at .65 RPM (1.54 minutes per revolution) with the
curve trending down.  I have taken many mind trips trying to rationalize
what I am observing.but all those roads are leading somewhere near
Albuquerque and I have no reason to go there (nice place though hihi). 


Let me know off line if you would like the graphics of my rotation study.


Mark Spencer, WA8SME

mspencer at arrl.org


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