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R: Satellite Downlink Power Combiners?




----- Original Message -----
From: Bob Bruninga <bruninga@usna.edu>
To: <amsat-bb@AMSAT.Org>
Sent: Monday, September 23, 2002 7:27 PM
Subject: [amsat-bb] Satellite Downlink Power Combiners?


> Question for the Experts:
>
> How does one combine four 2m satellilte transmitters to a common antenna?
> A Wilkenson power combiner comes to mind...
>
> But if the transmitters are NOT all phase coherent and are on seperate
> in-band frequencies, isn't half the power from each transmitter lost in
> the loads?  The text books always seem to use the example of combining
> multiple parallel amps (all with the objective of combining them all in
> phase...)...
>
> We want to have 4 separate 5W 2m XMTRS connected to a common downlink
> antenna. These XMTRS will be on different in-band frequencies so are not
> coherent or in phase.  A four-way wilkenson combiner is what we are
> considering, but not if we end up only getting 1.2W ultimately delivered
> to the antenna from each one's class C final.
>
> The text books say the power lost in the resistors is zero if all
> impedances are balanced, but when XMTRS are non phase coherent, then
> who knows what their impedance looks like on the other's design frequency.
>
> If not a wilkenson power combiner, then what do you use so that with four
> 5W xmtrs, each one gets its own 5W's delivered to the antenna
> independently?  I fear the answer may be a multicoupler where you have to
> have very High Q cavities such that each one only sees the antenna at its
> own frequency.  But then this is impossible to put into a small satellite,
> and besides all the freqs are within 200 KHz of each other....  Too close
> to get any isolation with cavities or helical resonators....
>
> Or combine at low level and then use a very linear amp?  ANd pay a big
> penalty in DC power?
>
> Expert opinions solicited...
>
> de WB4APR@amsat.org, Bob
>

Bob,

For the solution of your problem look please at the following articles:

1) "Linear Translators" by James Eagleson WB6JNN ,Ham Radio Magazine
     September 1983, pages 14 to 31

2) A new Transponder for Amateur Satellites by Piero Moroni i5TDJ, AMSAT
     Newsletter Nr2 June 1978 pages 6 to 9

Martha should have the reference Nr 2 in the AMSAT-NA archive

All the above circuits combines at low level and than uses a very linear
amplifier.

The reference Nr 2 has been succesfully used in four experimental ARTOB
italian Amateur Radio Transponder On Balloon  Linear Transponder flying
at an altitude of about 40 km from Sicily to  Huelva in south of  Spain
beginning from early 1984

73" de i8CVS Domenico

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