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@mindspring.com; k9jkm@comcast.net; AMSAT-BB@amsat.org From: vk3jed@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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