[amsat-bb] Re: XW-1 QSO and packet attempt

Andrew Glasbrenner glasbrenner at mindspring.com
Sun Dec 20 19:37:47 PST 2009

Sebastian wrote:
> I think Drew (KO4MA) and I had the pleasure of completing the first QSO on the FM repeater of XW-1 tonight from North America.  Signals were extremely strong, yet unfortunately very few stations were heard on the downlink.
> Just seconds after Drew and I chatted, we heard/worked Jay (AA4FL), Rick (WA4NVM) and John (K8YSE).  Luc (VE2DWE) has some magic in his antennas, as I consistently heard him pretty much all through the pass.
> I heard Drew mention that perhaps due to the PL tone and the large number of stations trying to use the repeater, very few stations were able to make a QSO. 
It was really reminiscent of the first week or so on AO-51. Signals were 
great, especially considering the altitude/slant range. However, and no 
offense to the designers, the sheer number of folks trying to access the 
satellite illustrates the fatal flaw with this sort of PL system. Two or 
more signals of nearly the same strength at the same time, and no one 
gets through, which leads to some users holding the mike down until they 
do. I also wonder how many unattended packet beacons there are out there 
on 145.825, with no tone. We might take a listen sometime with AO-51 to 
get an idea. What we did with AO-51, although we haven't implemented it 
yet for other reasons, is to use the PL decoder output to tell the 
flight computer to turn the transmitter on for n minutes, and pass all 
audio regardless of tone. This will let us use the PL to conserve power 
when no users are there, but mitigates this logjam effect somewhat. This 
is where full duplex really becomes worthwhile, to prevent QRMing other 

I of course have no idea if the hardware on XW-1, or SO-67 for that 
matter, would support this sort of system if reprogrammed, but it would 
be nice to see it designed into future spacecraft. This was part of the 
lessons learned paper I presented at symposium this year.

After the newness wears off and the crowd thins, the problem won't be so 

Congratulations and thanks again to Alan and the AMSAT-China group for a 
fine spacecraft, with a really fine orbit.

73, Drew KO4MA

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