Quoting Patrick McGrane N2OEQ@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 http://www.amsat-dl.org//index.php?option=com_content&task=view&id=6... 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 VE9QRP