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SSPB Problem

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Posts: 5
May 13th, 2012 at 8:52am  
Hi Guys,

I have strange prob. with my 1+1 redundant SSPB system, the SSPB is transmitting a very week carrier for a while and then it gets stopped. it is a 25W redundant SSPB used for iDirect service. could any one advice me what I should do to solve the prob?
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Eric Johnston
Senior Member

Posts: 2109
Reply #1 - May 13th, 2012 at 10:09am  
Insert an L band splitter in the transmit cable from the iDirect modem and monitor the transmit carrier at L band.

Insert a very high loss cross-waveguide coupler in the waveguide to the antenna.  Monitor the transmit carrier. Tell the NOC what you are doing first.

Is the modem TX carrier at the expected level, the same as what the modem screen says ?

If the modem TX carrier disappears then the "fault" is probably in the iDirect modem or the software controlling it.  Was the modem told to turn off the carrier by the hub ?

Does the SSPB output carrier disappear when you see loss of signal ?

If the TX carrier continues normally from the iDirect modem and the signal out of the SSPB disappears then reduce the modem output level to a very low level and try using the other half of the redundant system.  The reason for reducing the level is to be certain that you are not overdriving the SSPB and potentially damaging it. Do you have any monitoring of the SSPB to say what input/output levels, power supply volts, currents, temperature etc ?

Always do initial tests at very low level and increase cautiously.  A "weak" signal may not be weak at all but extremely powerful and you are getting a false indication - e.g. a high error rate due to distortion or leakage via a muting system which has panicked and cutdown the carrier to save the SSPB from burn out.

Investigate to see if the redudancy switch system is working correctly. Both input and output should change over together. The spare waveguide switch output port should go to a suitably rated dummy load.  There is the possibility that the weak carrier you are seeing is switch leakage from a 25W carrier being put into a dummy load instead of the feed waveguide.  Is the load hot ?  Is there excessive VSWR and is the on-line SSPB muting itself ?

After getting approval from the NOC, use CW carriers for testing.  Ther are much easier to measure accurately, are less likely to damage the SSPA than a modulated carrier, BUT do cause interference to the other polarisation and to the adjacent satellites - so you need approval first.

Best regards, Eric.
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