�� . �� : http://www.naic.edu/~phil/rfi/miscdevice/compressorMon/compressorMon.html
�� : Fri Jun 10 22:55:04 2011
�� : Tue Feb 5 17:21:03 2013
��:
�� : � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �

Compressor monitor

Compressor monitor system (CMS)

Links :
06jun11: testing the compressor monitor system on the telescope.
14apr11: testing the compressor monitor system in the lab

06jun11: on telescope testing of CMS. (top)

The 327 vlbi run on 05jun11 reported a 1 Mhz comb in the data. On 06jun11 we did some tests to see if the problem was coming from the compressor monitor system (which had been turned on during the 05jun11).
The setup was:

327 receiver, center freq 327 Mhz, 302=352 filter installed
mock spectrometer: 43 Mhz bandwidth, 8192 channels (5Khz resolution), cfr 327 Mhz, 1 second dumps.
Since the compressor monitor is on the dome, the az,za position should not make much difference.
Data was taken for about 750 seconds.

Around second 400 to 500 seconds, willie iguina openned the huffman box of the compressor monitor to get access to turn off the device.
At 542 seconds the compressor monitor system was turned off.

Processing the data:

a bandpass to flatten the spectrum was computed by:

average the 750 seconds of data
do a robust fit (throwing out outliers) using a first order polynomial and a 43 order harmonic function.
divide each of the 1 second integrations by the bandpass generated by the fitting (then remove 1.)
For each 1 second record remove the median value (to get rid of continuum source drifting through the beam).

I used a fit for the bandpass correction instead of a median bandpass so that contstant rfi would not get removed.

The image shows the dynamic spectra for the 750 seconds of data (.gif):

the image was made using polB.
the horizontal dashed line at 542 seconds is where the compressor monitor system was turned off.
The image has been smoothed and decimated by 6 so that the image will fit on the computer screen. This changes the resolution bandwidth from 5 khz to 30khz.
There are no obvious lines that stop at this point.

The plot shows average spectrum with the compressor monitor on and off (.ps) (.pdf):

Top frame: polA, bottom frame polB.
The black line is the average (500 seconds) with the compressor monitor on.
The red line is the average (250 seconds) with the compressor monitor off.
A birdie from the compressor monitor would have a black spike with no corresponding red spike. I don't see any of these.

Summary:

No birdies were seen from the compressor monitor dynamic spectra using 1 second and 30 Khz resolution.
An average spectra of 250 seconds and 5 Khz resolution also showed no birdies from the compressor monitor.

processing: x101/110606/chkcompressormon.pro

14/15apr11:Compressor monitoring system in the lab (top)

The Compressor monitoring system was tested for rfi by luis Quintero 14apr11 in the screened room. It was retested 15apr11 after some added shielding.The setup was:

Compressor monitor system inside huffman box.
agilent E4445A spectrum analyzer, 601 channels, and preamp on.
1 MHz to 10 Ghz. I've included the data from DC to 6gHz.
Probes used:

ETS model 7405 902 probe: magnetic field. upper resonance > 1.5 Ghz
ETS model 7405 904 probe: E-field probe upper resonance > 1Ghz
A separate set of plots was made for each of the 2 probles used.

Move the probe around the device looking for maximum value (spectrum analzyer set to max hold).

Do the tests with the huffman box open and repeat it with the huffman box closed.

The plots show rfi from the compressor monitor system:

Page 1-2: scan 0 to 1500 MHz H,E probes
Page 3-4: scan 1500 to 6000MHz H,Eprobes
Page 5-6:higher resolution scans for 327,430,750, and sband narrow receivers. H,Eprobes
14apr11: rfi with huffman box open (.ps) (.pdf)

the 902 probes measures the H field, the 904 probe measures the Efield
lots of rfi 0 to 500 MHz..
62.4964 MHz comb continues to 3 Ghz.
Wide bump around 1070.
Some of the wider rfi in the hi-res spectra move in freq between the 902 and 904 measurements. The might not be associated with the device.

14apr11: rfi with huffman box closed (.ps) (.pdf)

Below 100 MHz lots of rfi.

Luis mentioned that the below 400 MHz the problem is the switching power supply.

Comb not visible.

15apr11:rfi with huffman box closed after luis did some shielding (.ps) (.pdf):

luis added some shielding to the devices in the huffman box (.pdf) and then remeasured the rfi on 15apr11.
data was only measured up to 2500 MHz on this data with the huffman box closed.
902 probe: rfi below 100 MHz way down
904 probe: rif below 100 MHz actually got stronger.

either the probes looked at different spots between 14,15 closed or ??

Summary:

The Compressor monitor has a 62.4964 MHz comb

With the box open this extends up to 3GhZ.
With the box closed it is not seen.

With the box closed there is strong rfi 0 to 125 MHz probably coming from the switching power supply.

After some additional shielding of the device, the H field rfi belwo 125 MHz went way down while the E field measurement went up.

processing: x101/110415/docms.pro

home_~phil