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Transponder design and schematics


I have been working on a linear transponder 435 MHz up / 145 MHz and 2401
MHz down. I have explored a couple of different design like:

1. Downconverting to a low IF where filtering and amplification takes place
and then upconverting.
2. Using an analog I/Q demod centered at the 435 MHz band center and doing
all of the filtering and amplification at audio. The I/Q then drives an I/Q
modulator at 145 MHz.
3. Doing an all digital design based on our work at www.rfspace.com. This
design uses a digital downconverter and digital upconverter with some
processing between them.
4. A transponder with fixed gain and automatic intercept point adjustment.
That way when a big signal comes along, the current and voltage to the final
stages are adjusted to support the higher power while not attenuating the
little guys. This transponder also uses less power when not being used. I am
still working on this idea.
5. A transponder with linear input and FM output where the whole input band
is FM modulated onto a carrier. This approached can be easily AFCed at the

I want to know if anyone has access to the transponder schematics from the
Fuji, AO or RS satellites. I do not whant to reinvent the wheel. I am
looking at maybe borrowing some ideas to build a transponder that is
efficient, sensitive and very simple and does not have unnecessary bells and
whistles. The idea is to have something small that can be placed in
satellites that have unused payload space.


Pieter Ibelings

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