Hello robert- thank you for a very well written explanation of the SDX system. I understand it better now. I'm still of the opinion that the satellites should be kept as simple as possible to increase reliability and life but I also believe in democracy and it sounds like it works well here. I dont agree with your "outdated" label of the old technology. Then again, I dont buy a new car every 5 years. Oscar 7 is a good example of the ruggedness of the old technology. You're a very good tech writer, thanks for taking the time to explain, pat n2oeq

------- Original Message -------

From : Robert McGwier[mailto:rwmcgwier@gmail.com]

Sent : 3/24/2007 11:54:26 AM To : vk3jed@gmail.com Cc : k8ocl@arrl.net; Patrick.McGrane@aceweb.com; amsat-bb@amsat.org Subject : RE: [amsat-bb] Re: P3E transponder and launch

Thanks to everyone for the comments, concerns, and thoughtful remarks.

SDX is no magic bullet. It cannot perform any better than the analog hardware around it and our careful work on doing the mixed signal work and even more careful work to make sure it survives the rigors of traveling through Van Allan radiation belts four times a day!

That said, it provides us with several things. The DESIGN of the SDX will allow us to use a high dynamic range receiver in comparison to those we have flown before and to actually realize the potential presented to us by this receiver.

If we have this high dynamic range receiver, we can use a much lower noise floor and wider dynamic range transmitter to provide cleaner signals. This will be evidenced, if we do it right, by us no longer hearing the noise floor of the transponder. Next, if we have sufficient DSP horse power, we will be able to mitigate PAVE PAWS pulses by doing pulse detection and subtraction. THIS IS A LINEAR OPERATION. It will be much nicer than clipping. If the pulses get so large that we are clipping then all bets are off but with an 80 dB dynamic range receiver, this will be much less likely to happen. Stephensen has done a detailed analysis of this and this is available on Eaglepedia.

Next we are designing in the ability to provide the most capable HELAPS we have ever done. HELAPS is high efficiency linear amplification by parametric synthesis. Technical papers by Karl are on both the AMSAT and AMSAT-DL web sites. It is envelope elimination and restoration amplification. It allows us to use very high efficiency nonlinear amplifiers in the transmit chain and then have the "envelope" of the hard limited signals from the transponder imposed on the signal just before it hits the antenna by modulating the voltage on the last or last few stages. If we do the final transistors and the driver, we can get VERY high efficiency compared to what we have achieved in the past WITHOUT all of the poor IMD we lived with to get the efficiency. SDX is THE enabler in this.

SDX provides us with the ability to easily find all alligators and impose our will on them. There will simply be no benefit to running an EIRP that is larger than we decide to allow because YOUR INDIVIDUAL signal will be suppressed!

Juan Rivera, WA6HTP, and his team are building the fancy receiver which has been designed by KD6OZH and peer reviewed to death by others. Parts are being purchased NOW and the goal is to have four soon. We are building at least one to fit the P3E box shape.

Marc Franco, N2UO, has designed, using modern parts that are very difficult to get without connections, a serious 2 meter final stage. It will provide the highest efficiency 2 meter transmitter we have ever flown for HELAPS.

Steve Hendricksen, a TCNJ engineering student, design a S band amplifier in a senior engineering project directed study for Marc, Al Katz (K2UYH), and I. He submitted this for competition in an amplifier efficiency contest. He received an honorable mention and came in very high in the rankings. However, his amplifier was the only one well in excess of the minimum power, at 2.4 GHz rather than 1.0 GHz (the contest minimum).

As always there is the balance between "new with great promise but untried" and "the old, standard but somewhat outdated". We can have this argument all year and it will never be easily resolved.

AMSAT-UK has agreed to provide SDX software working with P3E and Eagle teams. They have agreed to copy the AO-13 RF if none of these fancier elements shows up and works. AMSAT-DL is planning for these contingencies.

So we have arranged for a small trial: Suisat-2 will carry a low power SDX with a few of these capabilities. We are planning a very large AMSAT engineering activity for this coming summer which you will hear more about in the coming weeks.

I could go on but what I want to promise is this: I have been extremely busy both professionally, personally, and with AMSAT things and I have not done an Engineering Notebook in a while. I will do a detailed paper on this for the next journal and it will be in my engineering notebook. Following publication I will put the document with more backing material on Eaglepeda as well and give it to AMSAT-DL for both our sites.

Bob N4H

Tony Langdon wrote:

At 10:46 AM 3/24/2007, John Champa wrote:

...

Guys,

The reports I have seen is that the SDX sounded BETTER than the traditional analog transponder. Bob, N4HY, can confirm that fact?

I wouldn't be surprised at this one at all.

...

Anything other than SDX would be a step-backward for AMSAT.

That's my viewpoint as well.

73 de VK3JED http://vkradio.com