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Message ID: 422     Entry time: Wed Dec 8 00:15:42 2010
Author: frank, tara 
Type: DailyProgress 
Category: BEAT 
Subject: LO phase noise 

Today we

1) checked if LO phase noise dominates at high f. It turned out that it is dominate at frequency above 1kHz.

2) found out that  RFPD for current RCAV has no 35.5 resonsnce,The calibration for input range at 10kHz is 7.55 kHz/ V

3) tried to float the table, but the pressure is not enough. The gauge reads 2.5 bars.


As we are hunting down various noise sources in our setup, we have to check every components of the setup.


1) As LO phase noise for the current setup (carrier:160MHz, input range:100kHz )has never been measured,

   we tried to see if it actually the limiting source. By  reducing input range of the Marconi, we might see the change of the beat spectrum.

     The regular setting for input range is 100kHz, which was verified to produce real beat noise upto 10kHz.

we changed to 10kHz input range, and measured the beat noise at gain x5, x10, and x20. 

 Since we checked that at gain 10 and gain 20, the noise spectrum, upto 3kHz, does not change with the gain setup.

We can be sure that, at gain x20, the signal we measure up to 3 kHz represents the real beat noise, see plot 1,

the red circle shows where the noise spectrum at gain x20, still similar to that of x10..

The calibration for 10kHz input range is 7.55 kHz/VWe see that at high f from 500Hz and above, LO phase noise is dominating.

[Wed Dec 08 13:39:24 2010 ]

I measured the beat noise spectrum from 1 - 3 kHz and plotted it on top of the usual noise budget. see fig 3.


2) We measured the TF of RFPD for PMC, RCAV, and ACAV. 

 By modulating the intensity of the laser with the EAOM, we can measure the RF response at the RFPD for each cavity.

The source out is split into two paths, one to EAOM, another one is used for reference.

PMC-RFPD has a resonance peak around 18.2 MHz.

ACAV_RFPD has a resonance around 36.3 MHz,

RCAV-RFPD does not have a peak at 35.5 MHz as it should have.


We will try to switch RCAV RFPD with that of ACAV to get some extra gain. This should give FSS loop some extra gains.

I'll bring it to 40m and use Jenne's laser to test it again and measure a proper TF. Besides, EAOM might not work well at that high frequency.


2.1) Just for fun, we measure the beat noise spectrum without the PMC installed (we removed it when measuring the TF of ACAV/RCAV RFPD), there is no significant change between PMC and no PMC. see plot 2


3) we tried to float the table. Alas, the 2.5 bar pressure from the valve is not enough. Plus one of the table leg (the one that is close to the fume hood) seems to be broken.

The air suddenly leaks from that leg after we turned on the pressure for 30 mins.

Attachment 1: 10kHzspan.png  26 kB  Uploaded Wed Dec 8 01:19:57 2010  | Hide | Hide all
Attachment 2: noPMC.png  46 kB  Uploaded Wed Dec 8 01:42:59 2010  | Hide | Hide all
Attachment 3: beat_10kHz.png  44 kB  Uploaded Wed Dec 8 13:38:37 2010  | Hide | Hide all
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