Louis McFadin wrote:
For 43 of the Hittite devices it would take 132 w to deliver 43w of RF.  This doesn't count the circuitry needed to drive the finals or other spacecraft requirements.
This will also present a huge thermal problem with the need to dump around 100w of heat on the top of the spacecraft.
At least 250w of solar capacity would be needed to support this based on current requirements.
The only reason I have "suggested" the linear Hittite parts is that
  1. They exist
  2. They work
  3. They are cheap
I would suggest that an optimized amplifier is possible and that it will be much better on efficiency. About a year ago, we had a meeting in NJ of east-coast RF designers at Al Katz (K2UYH) shop. At that meeting we had several microwave RF power designers: Al, Marc Franco (N2UO) and Paul Drexler (W2PED). Al's business involves tweaking amplifiers for optimum performance, Marc was Al's PhD student working on the same topic, and Paul's specialty is in solid-state microwave amplifiers. On the cover of an AMSAT Journal last year was a high efficiency S-band amplifier done as a project by one of Al's undergraduate students. So I do not see the C-band PA being a show-stopper. However, even if an optimized amplifier is developed, the C-band system will still need at least 100 watts of DC power and it will create at least 50-60 watts of heat. That's still, best case, about 50% of the "huge thermal problem"!

For the rest of the group I pose a question: If we assume that we are going to modulate the downlink with BPSK, can we get away with hard limiting (i.e. Class-C) amplifier? Do we really care about occupying a spectrum about twice as wide as "best engineering practice"?

73, Tom