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RE: Satellite Power Combiners?

How do you keep signals in phase, if they are at different frequencies?

Not trying to make trouble, this just seems to be a problem.


At 08:51 AM 9/24/02 +0930, you wrote:
>Im trying to think why this *cant* be done with 6 2-way combiners, with
>theoretically no loss.
>(Using four-port type combiner).
>(It would be much easier with a pic, but Im no good at ascii pics, so please
>bear an explanation in words.)
>The way I undersand these combiners is that if each port is (imagined) at
>the corner of a square, then there is hi isolation between the diagonal
>opposed ports, and ~3 dB split to the 2 adjacent ports, UNLESS the signal on
>the diagonal port is identical and in phase, in which case it all goes to
>one adjacent port, and none to the other adjacent port. (imagine a splitter
>working in reverse)
>That said, heres how my idea works.. we put 2 of the 4 signals we want to a
>combine, into 2 (oppososite) ports of 1 combiner....now we get the 2
>(identical but mis-phased?) outputs of its 2 'output' ports, and phase them
>correctly so they are in phase, such that when we feed them into a second
>combiner, they combine to only appear at one of the 2 output ports.
>Now we do the same with the other 2 signals (combine to one), THEN we should
>now have 2 physically separate signals, each one a linear combination of 2
>signals. If we appaly the same theory to THESE 2 signals (ie combine with 2
>combiners) , we can be left with 1 signal being a combination of 4 parts.
>Im not saying this is the most efficient way of doing this, I suspect a
>simpler circuit could acheive the same goal.
>Realisation could possibly be done in stripline on high Er board.
>anyway..back to work.
>DAve M. (VK5DSM)
>-----Original Message-----
>From: Bob Bruninga [mailto:bruninga@usna.edu]
>Sent: Tuesday, 24 September 2002 02:57
>To: amsat-bb@AMSAT.Org
>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
>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
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