[amsat-bb] Re: P3E transponder and launch

Bruce Robertson broberts at mta.ca
Fri Mar 23 05:29:54 PST 2007

Quoting Patrick McGrane <N2OEQ at aceweb.com>:

> Greetings from pat n2oeq
> I have been looking forward to the launch of P3E which I thought was
> going to be this year.
> I am concerned about the germans use of the SDR technology over william
> Liejanier's transponder design.
> I am of the belief that signal processing presents a loss in the path,
> please correct me if I'm wrong.
> Williams Hamsat transponder is excellant and made me very interested in
> P3E.
> Besides making the voice unnatural, are other modes allowed through the
> SDR transponder?
> Does the Helaps system compensate for the loss?
> I'm of the Keep it simple discipline as once its up there nothing can be
> done to fix it.
> If amsat-dl is monitoring , please update your website and provide a
> direct Paypal donation utility.
> Thanks to amsat-na for the donation to P3E recently. 73, pat

The amsat-dl article "Launches Speak Louder Than Words", published in May 2006
noted that Nov. 2008 was the first relatively secure date. I believe more
recent sources have suggested that the bird will be ready in Spring or
Summer of this year. Perhaps there is some hope that a more recent launch
opportunity will arise.

>From my reading, and I'm not an expert, SDX technology is predicted to be
indistinguishable from a linear xponder to the ground station: I have read
no account of entailed losses. What it *does* aim to provide is a newly
flexible and configurable bent pipe. One obvious application is to limit
the amount of output power in a given portion of the passband, thereby
reducing the impact of alligator stations. The audio files posted on this
list indicate no unnatural artifacts to my ear, and such transponders are
routinely built to operate with varying modulation schemes. 

As this technology matures, one could imagine groundstations developing
'applets' for the SDX. For instance, imagine an bit of SDX code that
listens on a certain very small passband and responds to any CW signal with
a report that indicates that signal's average power in dBm or dB above
noise, or what have you. This would be an invaluable tool for calibrating a
station! What if the report were sent three times, each signal 10 dB lower
than the previous (something like the IARU beacons); then you'd have some
hard numbers on how your Field Day station was performing on both uplink
and downlink.

My point is that SDX allows us to dream of these things, and potentially to
implement them even after the bird is up. Yes, it entails a risk. We're
fortunate to be able to mitigate this risk: SuitSatII will fly with SDX
on-board so that we can test this technology. To my mind, the  satellite
service/hobby is a branch of the hobby that continues to fulfill the
experimental origins of amateur radio. We need to do so prudently, given
the cost of launching the hardware into space, but I think the SDX concept
fits nicely within that curve.

73, Bruce

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