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RX setups for AO-40



All,

I'd like to make some general SWL comments about RX setups.  Most of this
comes from the SWLing that I've done on AO40 over the last couple of passes.

General observations
 - Squint is important and will effect the signal quality
 - Spin is also import as the Spin modulation can be seen and heard and the
sat is running at about 7RPM
 - Distance.... If you don't have a GOOD RX setup, you aren't going to hear
anything at apogee or really beyond about 40K Km
 - Distance to the bird is measured in two lengths - The distance from your
station and the distance directly above the earth, don't get the two mixed
up in your head


RX observations
 - if you can't hear the MB on 2401.323 +- doppler, you are no way going to
hear stations from the sat.
 - most of the stations that I've listened too are at least 2S units down
from the Beacon in strength (relative to my S meter)
 - when the transponder is on, you have 2 and sometimes 3 frequencies to
check.  a) the S2 MB at 2401.323; b) the S1 MB at (check the table +- a
bunch as I don't have a qualified reference; c) the GB on S1 (see S1 MB
notes previous).  You can also check the RUDAK freq.  it's around .750 on
both S1 and S2.  RUDAK is on S2 when the transponder is off and on S1 when
the transponder is on.  Remember this is 9k6 and FM for RUDAK.
 - if you have a noise floor on your S meter when you have no signal...
please reference that as S0 and indicate all signals as positive reference
from that.  Telling someone that you are S7 when you are running an S5 NF is
very misleading.

My last comment and this is going to sound preachy... Sorry about that.
 - The NF of your first stage sets the overall system NF for your RX system.
So if you are using a Drake with 3.x NF, you will give away almost 3db to
those of us running the SSB or other .5-1db Downconverters
 - If you are one of those that are running the converted MMDS
downconverters.. Please think about the following.  If your RX system is
artificially desensed, for sensitivity, with the NF of your RX system.
Please don't "turn up the TX power" to overcome it.
 - Please help those that are trying to setup and test with equipment
reports when you give signal reports.  I tried to be heard on a converted
MMDS today and I kept getting "we can barely hear you" reports... I then had
a fellow ham tune up on his 1db NF converter with a good antenna and I was
S7 (against an s1 noise floor)... I was able to drop the power to 5W and
still be heard above the noise
- Just because you can be heard does *NOT* mean you can hear!  While the sat
if probably very linear in input to output, your RX system complicates this
equation a bunch

Couple of tips.
 - find someone that has "pretty good" hearing ability and use them to
reference your uplink power.  Then reference that to your hearing ability
and make improvements.
 - improvements can be made in the following areas. a) Downconverter - the
lower the noise floor the better; b) coax between the DC and you - this is
where you'll pickup local noise from leaky cable systems, RFI, etc. -
shielding and more of it are better.
 - Antenna gain - it's becoming pretty apparent that you need 15db or
greater to work beyond 40K and to go to apogee you need 20 or better.  The
short Helix's are in the lower range, not higher

Hope this helps... they are just general observations, but some that I've
seen in action.

For reference, I run the following on 2.4 Down.
52 Element loop yagi from directivesystems.com - 21dbi linear (mounted for
horizontal), on an 8' boom
SSB UEK3000SAT with 432 IF (this is why I can't get on the bird right now...
made the wrong choice unless the command teams let's the V uplink work
sometime soon??) it's .7db NF and 30db of gain

Actual reference.
 - At apogee at 65K km (away from me), I copy the beacon about S2-3 and
about 30% effec on the CRC telem
 - tonight will be a good test of what I can hear at apogee on this setup.
At AOS, the sat will be 65K out and the transponder will have just turned
on.

We'll see :).
Alan

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