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Transponder noise detectable



Hello dear all!

Yes! There are stations detecting the transponder noise floor with
available equipement. With my 60 cm dish (old X-band TV), a
"quick-hack" 2 1/2 turn feed described by G3RUH, an 1.5 dB NF (20 dB
G) preamp, 6 m coax and the downconverter of 2.5 dB NF (20 dB G) I can
hear at least the spin swoosh-swoosh of the S2-Downlink. As I'm not
satisfied with this (I want to hear the passband noise at all - not
only in the ups), the new preamp with 0.7 dB NF and 30 dB G is ready
to be mounted soon.  This will give another few dBs in S/N. All
electronic components are standard devices available on the market (at
least in DL) for less money than the low-noise pre-amp I used for mode
B on AO-10 and AO-13.

When comparing predicted equipement (e.g. in an article I wrote prior
to launch) with the actual situation please keep in mind what has been
mentioned by others on the bb beforehand:
- The apogee height has increased by several
  thousand kilometers.
- The S2-TX antenna has 8 dB less gain than S1, for
  which the predictions were made.
- As AO-40 isn't yet 3-axis stabilized, we have times
  with off-pointing antennas.

The downlink signals of AO-40 are already much better as what I got
from AO-13 and that with the restrictions above. As we know S1 is
working, we'll get at least that improvement in later operations.
Assuming 3-axis stabilization will work in the future the off-pointing
problem will dissapear as well. On a rough calcutlation we could see
the S2-TX with squints below 20 deg from MA 15 to 240 (87% of the
orbit) then. And near apogee, where it is needed, we could have
several hours (40% of an orbit) of S1-operation with useful squints
below 7 deg.

Another word to the U-uplink. One morning I noticed me all alone with
the MB on the transponder and could do some tests with AGC and LEILA.
Squint was around 8 deg, the satellite was near apogee 60 000 kms
away. The results are:
- With 400 W eirpc (the maximum my rig produces) I drove the U-AGC
  between 4.5 and 6 dB, but didn't reach the MB strength at all.
- Reducing power down to 100 W eirpc (8 W out, -2 dB cable loss,
  13 dBi antenna gain) gave an AGC-reading of -0.3 to 1 dB.
- Even the 100 W signal was readable without any problems
  with the RX above.
- LEILA neither marked nor notched my signal.

This uplink power of 100 W eirpc is exactly what pre-launch
calculations said. Please note that there were already SSB-QSOs on
AO-40 with stations running only 20 W eirpc!

73 and good luck with AO-40.
Amateur-radio isn't plug'n'play - it's experimental!

Frank
DL6DBN/AA9KJ

* eirpc = Effective Isotropic Radiated Power Circular

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