[amsat-bb] : Re: BY70-1 not heard

N6RFM1 gmail n6rfm1 at gmail.com
Sun Jan 8 21:00:50 UTC 2017


Hi Paul and AMSAT friends,

It's really great to hear BY70-1 getting lots of use.  Lots of familiar
calls and some new ones.  Perfect.

Indeed, Scott K4KDR and I have recently made several coordinated attempts to
collect BY70-1 telemetry and camera pictures.   This would not have been
even possible without the support of Mingchuan BG2BHC (as a project team
representative, for GNU radio support and example wav format command files),
Dani EA4GPZ (for authoring open source GNU radio blocks, and hosting a
fantastic blog which describes how much of this works), and the BY70-1
project team. 

We have made several attempts over the past few days during favorable passes
for us.  So far, we have received some good telemetry, been able to command
the satellite to take a picture and then download a few pieces of the JPG.
Unfortunately, so far we have only fragments of JPG data.  If more than a
few packets in the JPG file data stream are lost, the JPG image cannot be
reconstructed.   For reasons we do not understand, either the downlink data
stream stops, is disrupted or BY70-1 resets.  It may even be our ground
station hardware limitations.  We don't quite know.  We do hope however that
some of our experiences will guide future developments.   For example, as
Dani suggests SSDV which has error detection and correction capability.

For those interested and key point, BY70-1 will only accept a camera command
after 30 seconds of transponder non-use.  Given the popularity of BY70-1,
which is great and what we all want, Scott and I have had a few chances to
send camera commands during such "quiet times" or > 30 periods on non-use.
But again, we are delighted BY70-1 is popular and being used. 

What you may have heard was the satellite re-transmitting  my request to
"take and send" a picture.  These uplink commands are in FM and last a few
seconds.  If successful,  the satellite switches modes and starts picture
transmissions in SSB mode on the downlink.  These last for ~10 - 15 seconds.
Then we hear the transponder come right back on.  You might not even notice
between sips of coffee (or whatever!)

Once a related camera mode has been activated, there is a 10 minute
countdown before another such request will be accepted.  As a practical
matter, with the 10 minute camera watchdog, those interested in getting a
picture really have one shot/pass and only if the transponder is quiet for
the >30 second period.

It's really great to hear everyone using BY70-1.  That's what it's all
about.  And thanks to Scott K4KDR for being a great partner on this little
project!

Of course, I've made few Qs myself!  I must say the audio quality is amazing
to my ears.   One last thing Paul.  I need to work you on BY70-1!  :-)

73,

Bob





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