[amsat-bb] Re: P3E transponder and launch

Robert McGwier rwmcgwier at gmail.com
Sat Mar 24 07:54:26 PST 2007

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.


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

AMSAT Director and VP Engineering. Member: ARRL, AMSAT-DL,
"Taking fun as simply fun and earnestness in earnest shows
how thoroughly thou none of the two discernest." - Piet Hine

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