[amsat-bb] Re: AO-07 healthy CW

[Sil - ZL2CIA]

Hi,

Firstly, thanks to Mineo Wakita (JE9PEL), Gary Halstead (K8KFJ) and
Martin Gillen (VA3SIE) for the reception, copying, and decoding the data
from AO-07.

I remember some of the discussion posted here, when AO-07 started
working again. The consensus seemed to be that the satellite had failed
25 years previously because too many of the NiCd cells in the battery
had become short circuited (as NiCd do with time). This had caused the
battery voltage to fall to a level too low to operate the transponder.
Time,(and perhaps corrosion caused by the battery chemicals) had
eventually created an open circuit and the satellite was now operating
directly from the solar panels. Certainly, it goes very dead once it is
in darkness which rather supports this idea.

However, channel 2D of the telemetry shows a Battery Charge/Discharge
current of 80 ma. Since this is positive, I assume that it represents a
"charge" current. I see too that the "half battery voltage" is 2.4
volts, while the full battery voltage is 8.8 volts. So the dead battery
is behaving like a 110 ohm resistive load and consuming 0.704 watts.

This doubtless explains why the battery is at a toasty 60 C and most of
the rest of the satellite is at -46 C.

Also freezing is the 10m PA (channel 4B). This is not surprising since
it was "off" when JE9PEL recorded the CW. Yet this PA is drawing almost
0.8 amps of emitter current and producing nearly 6 watts of RF. It's
consumming 7 watts (8.8V * 0.8A)making the PA about 86% efficient). Does
this mean that the telementry is unreliable (fair enough, it a very old
satellite)?

The 2m PA (channel 5A) is a whole bunch warmer at -5 C. This makes sense
since the 2m transmitter was the one sending the data (or perhaps it's
installed next to the battery!) I presume that the 2m beacon signal is
simply injected into the 2m PA. Is this correct?

The battery voltages (and half battery voltages) give some indication of
where the remaining short circuit cells might be (in case anybody wants
to go up and fix them - actually, I will do that if someone can give me
a lift). I wondered about this in a sort of hypothetical way. I'm
curious for its own sake (and clearly have too much time on my hands).

I tried to find some details of the satellites design via google, but
didn't (I'm sure others will succeed in this).

I also looked in my own humble Ham library for details of the design,
but didn't find any.

I guess that the satellite battery consisted of cells in series and
batteries in parallel, or perhaps of cells in parallel then in series to
make a battery. Does anybody know exactly? Can anybody point me in the
right direction?

Sil - ZL2CIA