[amsat-bb] Just Checking... (AO-85)

Burns Fisher burns at fisher.cc
Mon Oct 12 15:19:29 UTC 2015

I'm sorry you did not like some of the replies on FB, but I would truly say
that this is a new bird, and the suggestion that you try multiple things
was not in jest, especially the bandwidth.  At some point as the bandwidth
you are transmitting gets wider, I'd guess that the voltage incoming from
the Rx to the A/D converter in the satellite exceeds its capabilities and
it clips.  But on the other hand if the B/W is too narrow, the gain will be
low.  I used 'narrow' in pre-flight testing from my HT but there is not
guarantee that the flight board will work exactly the same way.

A few other thoughts but no certain answers:

1) You said you heard other stations.  How much power do you have?  You
said HT, so I assume 5W or less.  Remember that FM is only single-channel
and usually the strongest signal wins.  (But also remember the standard
rule to use as little power as you can successfully use).  Some people have
managed with 5W HTs.  Others have not.

2) The bird seems to be tumbling quite a lot now.  The 70cm Rx antenna may
be even more subject to fading than the Tx antenna since the Rx is only on
one side, while the Tx uses both sides and the satellite itself to radiate
from.  (The thought about fading is somewhat informed speculation).

3) The 67Hz tone may take a second to kick on the transmitter but once it
is on it will stay on for the duration of the hang timer, which is one
minute.  So if you have have to kick the hang timer with low power it will
be harder due to fades.

4) When the hang timer is hanging (during that 60 seconds) if there is
nothing being received, the transponder is going to resend the noise that
it hears from the Rx.  When listening, I can tell the difference between
"no carrier from the satellite" and "satellite is transmitting the output
of a receiver that is receiving nothing".  The latter has fewer high
frequencies and fewer low frequencies, i.e. it is duller.  If you can hear
that difference, the latter case would be a good time to try to get in.  No
one is blocking you, and the hang timer is already running.

Seriously, detailed reports you make of both success and failure will be
helpful to others!


Burns W2BFJ
Fox-1 Flight Software

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