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Entry  Wed May 18 07:13:00 2011, Suresh, Update, RF System, Demod board measurements Demod_Board_measurements.pngDemod_Board_measurements.png
    Reply  Fri May 20 05:41:22 2011, Suresh, Update, RF System, Demod board measurements 
Message ID: 4755     Entry time: Fri May 20 05:41:22 2011     In reply to: 4736
Author: Suresh 
Type: Update 
Category: RF System 
Subject: Demod board measurements 

The POP110 board which had the large Amplitude and Phase unbalances was examined today.  It turned out that there was some stray solder which had connected the Sum port of the PSCQ-2-120 splitter to its body (ground).  After I removed that the amplitude unbalance was 0.3dB however the phase was 105deg.  The phase reduced to 90 deg only if the power on the splitter is around 19 dBm.  So removed the AT1 (10dB attenuator) and the phase unbalance dropped to 91 deg.  However this is not a sustainable solution as the ERA-5 max output is about 19.5 dBm.

As this is a side band power monitor (and not a length sensing RFPD), we can make do with a poorer phase.  I will therefore replace the AT1 and adjust the residual phase with cable delay lines.  

Quote:

I measured the amplitude and phase imbalances of the demod boards which have been modified.  This is just a basic health check.  We hope to use the script that Kiwamu is developing for a more accurate test.  The script can also use these measurements as a sanity check.  POP110  requires some further attention. 

Demod_Board_measurements.png

 

The RF distribution box outputs corresponding to the demod board (eg. AS55_LO --> AS55_demod) were used as LO sources.  The RF signal was generated with a Marconi and held a kHz away from the LO frequency.  The amplitude and phase unbalance were measured with SR785.  The RF Power meter was used to check the LO power in each case.

 

 

 

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