[amsat-bb] Re: BBsat Call for ideas

Greg D. ko6th_greg at hotmail.com
Mon Nov 24 23:14:37 PST 2008

Interesting idea.  But, there are really two fundamental ways to go here.

We can go low-tech; your idea.  Simple analog transponder.  Keep the housekeeping logic to a minimum to conserve power, maximize reliability, and minimize cost.  Clone AO-07, in effect, but with modern components.

The other direction would be to go the other way - high tech.  I for one would love to see a testbed for Eagle's ACP running in a LEO satellite, focusing, say, on the low bandwidth instant messaging application.  I know we can do this with APRS today, but only inefficiently.  We need a testbed to prove out both the modulation schemes necessary for improving the link budget, and the protocols for supporting the many multiple communications connections that this application demands.  

I have no idea if this is even possible in a Cubesat format satellite.  My only visibility into Eagle was at last year's AMSAT conference in Foster City (San Francisco area), but what I saw in the presentation really underscored the tag line on the AMSAT banner hanging over the conference hall entrance.  "We are rocket scientists!" (or words to that effect..)

Greg  KO6TH

> Date: Tue, 25 Nov 2008 13:38:03 +1100
> To: glasbrenner at mindspring.com; k9jkm at comcast.net; AMSAT-BB at amsat.org
> From: vk3jed at gmail.com
> Subject: [amsat-bb] Re: BBsat Call for ideas
> At 01:01 PM 11/25/2008, Andrew Glasbrenner wrote:
> >On the drive home from the symposium in Atlanta, I was thinking about a
> >cubesat with a "hybrid" voice repeater. My idea would use a 435 FM uplink
> >because it's easy to generate power enough on the ground, and the Doppler
> >shift moves QRM out of the uplink fast, it's FM and not picky about tuning,
> >and there aren't any illegal telephones that work on the uplink AFAIK. We'd
> >use a 2m SSB downlink, for a few reasons. 2m path loss is less, so given
> >similar antennas we'll get a better downlink. SSB is more efficient than FM,
> >and we also save power by not transmitting unless there is audio on the
> >uplink, a squelch of sorts.
> Interesting idea, except I do have one quibble - normally when there 
> is no signal on FM, there would be the background noise at high 
> level.  You would need to have squelch on the bird to cut the Tx power to zero.
> >No computer on my satellite either! We'd have some sort of hardware timer
> >that has to be reset every few days to keep the repeater running, so we
> >could meet FCC rules on control. Maybe PL or DTMF?
> >
> >Wouldn't it be neat to have one of these sitting on the shelf in case a
> >empty spot on a PPOD became available?
> Could be neat to have a simple bird to throw up at the drop of a 
> hat.  Also there are more 2m SSB radios than 70cm ones in service 
> down this way, so this is a goer in my book. :)
> 73 de VK3JED
> http://vkradio.com
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