[amsat-bb] Re: VO-52, Linear transponders and FM

Tony Langdon vk3jed at gmail.com
Mon Apr 23 16:04:39 PDT 2007

At 03:40 AM 4/24/2007, Bruce Robertson wrote:

>I can't speak for the rest of the world, but I'd say that in this neck of
>the woods, this approach has worked very well. I've only once or twice
>heard an FM signal on VO-52, no more often than other birds, and rare
>enough that I can assume it was by accident or ignorance.

I haven't checked this bird myself, because I lack 70cm SSB 
gear.  Australia is in probably a more unusual situation.  We have a 
relatively high penetration of VHF SSB gear, and a smaller, but 
significant amount of 70cm SSB radios out there.  However, we also 
have a very low population density, compared to the US or Europe.  I 
know when I was working RS-12/13, the only QSOs I had were those I 
had pre-arranged with local operators.  It's much easier to find 
someone on FM.  I believe there are some working Hamsat on SSB, from 
time to time, so it might be getting use here in SSB.  I doubt 
there's much, if any FM activity on this bird, I think the convention 
for this part of the world is SSB.

>Given VO-52 success in this score, I wonder:
>a) if the operators of other, future, LEO linear birds should likewise
>permit their use in FM over appropriate regions of the globe. Since FM is
>such a high duty cycle mode, I suspect usage and battery load statistics
>from Hamsat might be helpful in guiding others' choices in this matter.

Looks like there will be some useful lessons in here.

>b) what advantage there is in launching a FM-only bird when a linear one
>can be used in both modes. I assume there must be reasons of efficiency,
>etc. since the designers of KiwiSat, for example, are making circuitry for
>both modes.

Indeed, though we would need to formalise arrangements a bit more 
then.  For this part of the world, FM birds do serve a purpose, and 
that would need to be reflected in the local bandplan for any future 
linear satellites, if FM was going to be phased out.  In other words, 
a CW/SSB/FM transponder bandplan in a 40-50 kHz bandwidth might be 
needed here.  I'm sure a single FM QSO, 2 or 3 SSB QSOs and one or 2 
in CW would happily coexist at the same time down here.  Might also 
be room to experiment with managing the power sharing on a SDX as well.

Just thinking out loud...

73 de VK3JED

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