[amsat-bb] Re: BBsat Call for ideas
bruninga at usna.edu
Wed Nov 26 19:18:50 PST 2008
> One idea that hasn't been floated yet,
> is a 10m or 15m transmitter aboard bbSat.
We looked at that, but the problem is the order of magnitude fewer hams that have SSB transceivers. We went with a 10m uplink to an FM downlink so that any technician with nothing but an HT could hear it.
But then, you have gained nothing over the typical FM satellite b ecause of single-use. So that is why we went with PSK-31 on the 10m uplink so that the single 2m FM downlink would have as many as 30 ussers simultaneously (all sharing the 10 m PSK-31 3 KHz wide uplink.
> I therefore think a transponder that
> downlinked on these bands would be
> likely to 'broaden our base',
> I recognize that transmitting on
> such a long wavelength from a 10cm
> cube represents a technical challenge
Yes, the 4 foot whip deployment on our RAFT cubesat is what failed, not due to the antenna deployment but due to an ejection anomoly that spun the spacecraft out of contorl (80 RPM) from which the 4' whip antenna deployment could not work.
Receiving 10 meters on a terribly small and inefficient antenna is no big deal, because users on the ground would be uplinking with 25 watts, and being on 10m is 14 dB better link too, so uplink on 10m is easy.
So that is my preference, 3 KHz of PSK uplink on 10 meters with a single FM downlink with up to 30 users at a time... full duples too!
We flew this on PCSAT2 and on RAFT (though both had other problems leading to a lack of any meaningful success).
>challenge of mechanical engineering, not something that would run up
>against the limited power budget. I also vaguely have the impression
>that amplifiers, etc. are more efficient in the lower frequencies, so
>that might be a plus. (Not to mention reduced path loss.) Perhaps the
>effective power out would be so low that a directional antenna would
>be required on the ground. In which case, I'd say it was a no-go,
>since that would preclude too many of the new experimenters that we'd
>be hoping to snare on these bands.
>Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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