[amsat-bb] Re: Some Elmering requested for uplinking to ARISSAT-1

DF2MZ Edgar.Kaiser at t-online.de
Wed Nov 2 15:26:01 PDT 2011


I would strongly recommend using software controlled Doppler correction. 
It should be considered state of the art to correct uplink and downlink 
in order to keep the signal at fixed frequency in the satellites passband.

Before PCs became affordable, the manual standard procedure was to keep 
the rx frequency fixed and tune the tx until you hear yourself. I find 
it quite a nightmare and too many people are still doing it that way, 
performing very badly most of the time.
With up-to-date orbital elements and precisely synchronized PC clock I 
mostly manage to keep my downlink signal within the 200 Hz passband of 
the CW filter.

Your other points:
- Circular polarization should be fine and provide a more stable signal.
- The tranponder inverts, standard is to receive USB and transmit LSB
- It is much easier to find yourself by transmitting CW, best is a 
series of dits using an automatic keyer
- CW is anyway more efficient

One probably very important point is the missing UHF antenna on Arissat. 
I am using an FT-847, 50W and a 17el cross yagi, giving more than 1 KW 
ERP. I can hear myself fairly well, but not very stable. I hear the 
transponder noise floor very well, so the uplink seems to be the bottleneck.
There are reports about successful contacts with omni antennas, but it 
is probably not easy. The bird is pretty deaf.

Did you try your setup on VO52? This is an easy one and 25W to the 
Lindenblad should work very well. I think even AO7 mode B is easier than 
Arissat and also FO29 (this one is mode J or V/U transponder).

Like you, I am pretty new to the subject. I learned a lot by writing my 
own software for automatic Doppler correction for the FT-847 and for 
Rotor control. I am using NOVA for tracking.

Good luck,

Am 02.11.2011 22:12, schrieb Burns Fisher:
> Hi everyone,
> A few months ago I asked for help receiving the beacon on ARISSAT-1 and got
> a lot of helpful suggestions.  It turns out that my biggest problem was
> trying to listen from inside the house.  Moving the antenna outside was the
> key.  Heaven only knows what my shingles are made of...I never expected a
> problem!
> So now that I got pretty comfortable with receiving, it was time to step up
> from my little HT and get a somewhat more flexible and powerful rig.  The
> only satellite rigs still on the market are the ICOM 9100 and the Kenwood
> TS-2000 family.  I know about the birdies in the TS-2000, but I could not
> really afford the ICOM...maybe should have gone for a used 910 or
> something, but I did end up with a TS-2000.
> I still have the Eggbeater omni/circularly polarized 2m antenna for the
> downlink, and it is working great!  I get a nice strong signal from the FM
> beacon, and I'm able to hear people on the transponder.  I also either
> picked up the CW beacon or someone using CW on the transponder.   So
> anyway, the downlink is working fine.
> Now for the uplink:  I built myself a 70cm Parasitic Lindenblad per the
> plans of Tony, AA2TX.  I have it outside about 10 feet up, and an SWR meter
> shows something reasonable (1.3ish) so I guess I did not totally mess
> it up.  I can also hit the local repeater 5 miles away on fairly low power,
> etc.  The Lindenblad should be circularly polarized with kind of a
> donut-shaped pattern (more gain toward the horizon where the bird is
> further away, less overhead where it is closer).  But so far I have not
> been able to hear myself trying to contact ARISSAT.
> Here is what I tried:   I set the TS2000 to satellite mode, and set it up
> so I was transmitting in the middle of the transponder uplink band on USB.
> Then I started scanning through the downlink passband while transmitting
> ("W2BFJ, tuning") using the "RIT" control so that transmit frequency was
> not changing.  I was listening with LSB.  I heard another station weakly,
> but not myself.
> Can someone comment on my method, both in terms of technical goodness and
> good operating practice?  A couple specific questions:  1) Xmitting in the
> middle of the passband and just scanning, I should be able to at least
> briefly find myself without messing with doppler, right?  I was planning to
> lock the receive and transmit frequencies (constant sum) once I found
> myself and follow the doppler by hand, but I never got to that step.  2)
> I'm right that the sidebands are inverted from receive to xmit, right?  I
> think I would hear something even if that was wrong.  3) Finally, what
> about power?  How much have you required for success on ARRISAT?   I was
> running around 25W.  I could boost up to as high as 50, but I can only
> diddle so many knobs in 5 or 10 minutes :-)  3) I know a beam would be
> better, but trying to reduce variables, and pointing is one of them.
> Besides, I'm inside in my shack!  But has anyone successfully uplinked with
> an omni/circular?  I can always remove the parasitic elements and end up
> with a center-fed dipole to remove the circularity.  (Not sure how that
> would affect the impedance match...)
> Thanks!
> Burns, W2BFJ
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