encoder  Combs in 327 receiver.

11oct16: New encoder comb measured in screen room.
31jul09: az encoder combs. enc1,enc2 spacing is different.
03oct06 Initial report of comb: comb spacing, dynamic spectra.
04oct06 az, za and time dependence of comb
05oct06: compare comb with old and new encoders.

Note06: the comb was coming from the azimuth 2 encoder (on the ch side). A new encoder had been installed on 02aug06. The old type encoder also has this comb (but a lot weaker). The old style encoder was reinstalled 05oct06 around 1pm.

31jul09: Az encoder combs

    The 614 khz combs were seen in the 327 receiver. Data was taken on 31jul09 with the 327 receiver and the mock  spectrometer to test the rfi.

The setup:

    The power to the encoders/vertex shelter were then switched on /off while the data was being taken. The sequence was:

The processing:

A dynamic spectra was made for the 1500 seconds of data while the power was turned on,off (.gif):
Overplotting the spectra showing the birdie strength (.ps) (.pdf):


processing: x101/090731/azencbirdie.pro

03oct06 Initial report of comb  (top)

    A comb was seen in the 327 MHz receiver with a 614 Khz spacing. On 03oct06 data was taken with a 25 MHz bw, 2048 channels (24 kHz channel width after hanning smoothing), and one second dumps while the telescope was sitting at  az=229.25, za=10 degrees. One 25 MHz band was centered at 322 MHz while the second band was centered at 332 MHz.

    Dynamic spectra while sitting (.gif).

    Average spectra (.ps) (.pdf): The largest spike in this freq. range is at 316.418 MHz. The birdie at 313.5 is not part of the comb
processing: x101/061003/doit.pro

04oct06 az, za and time dependence of comb  (top)

    On 04oct06  the azimuth, zenith angle, and time dependence of the 614 Khz comb in the 327 receiver was measured. The comb element at 316.416 was used. A 395 Khz band with 2048 channels (385 hz resolution after hanning smoothing) was centered on the 316.416 MHz comb element. One second sampling was done. 3.8 khz about the center of the comb birdie was averaged and then plotted.
    The plots show the  az, , and time variation of the birdie (.ps) (.pdf):
processing: x101/061004/doit.pro

05oct06 compare comb from old and new encoder.  (top)

The new az encoder was replaced with the old version on 05oct06. On 05oct06 data was taken with the old encoder back in. The az/za was 270/10 (it would have been better to do this at za=18 where the birdie is stronger but i didn't have control of the az/za). 382 seconds of data was taken in the same format as 04oct06.  The plots show the comparison of the new and old encoders (.ps) (.pdf).
    Most of the comb elements are no longer seen with the old encoder back in. There are a few that show up in the 25 MHz band (with low resolution). We should see if these really belong to the encoder by monitoring them (with high resolution) while the encoders are shut off.
processing: x101/061005/doit.pro

Summary06:  (top)

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