28may13
27may13: azswings
28may13: birdie strength vs za
Updates:
- 28may13: source of
rfi:
- Using a helix and the
anritsu spectrum analyzer, we went through the platform
and dome looking for the birdies.
- the 1419.963675 and 1667.957345 MHz birdies were coming from the
"dust bin collector controller". This is next to the large
green dust bin collector at the center (bottom chord) of
the azimuth arm. The collector is used to suck up
the grit during the blasting (prior to the painting).
- There were a large
number of other narrow band birdies coming from this
device. the 1419 and 1667 were obvious because a2767 was
doing narrow band work at HI and OH.
- Maintenance had not
been turning this off when then finished painting/blasting
each day.
- Looking at data taken
on the telescope, the controller was left on :
- fri 24may13 till tues
27may13 (when i turned it off)
- tues: 21may13
probably on 22may13.. not sure how long it was left on
since no x111 data on 23may13
Intro:
Project a2767 reported
narrow band rfi near 1419.963 and 1667.957 MHz. Their setup used
a 1.5 Khz resolution channels. The 1419 MHz birdie was stronger
than the 1667 MHz birdie.
27may13:
azswings:
On 27may13 azimuth swings were done
to see if there was any azimuth dependence to the birdies. The
setup was:
- za=18 deg. az 270->640 at .4 degs/sec. CCW then CW spins
were done.
- lbw was used with the 1360-1470 and 1550-1820 MHz filters in
- The mock spectrometer was used. 3 boxes were used. The
setup for the 3 were:
- box 1:
- cfr=1419.90 MHz
- bw=.24576 MHz
- channel width: 30Hz
- box 2:
- cfr=1424.00 MHz
- bw=8.6015 MHz
- channel width:1.05Khz
- box 3:
- cfr=1667.9
- bw=.24576 MHz
- channel width: 30 Hz
- 1 second dumps were done. The pfb shift was set to noise
(instead of radar).
The dynamic spectra show the rfi as
a function of azimuth:
Dynamic
spectrum notes:
- The dynamic spectra were normalized by fitting at 31 order
harmonic to the median bandpass.
- The bump at the center each band is from DC.
- 4 of the birdies in each spectra come from baseband
birdies at the input to the a/d's in the mocks.
The plots show
the average
spectra as well as the azimuth dependence of the birdies:
(.ps) (
.pdf)
- Page 1: average spectra.
- The average spectra for each swing was computed.
- Black in the CCw swing, red is the CW swing
- polA,polB for the 1419.9 band is followed by polA,polB
of the 1667.9 band
- The dashed green lines are located the same distance
from the center of the band for each frequency.
These birdies are generated in the mock boxes at baseband. (39
and 78 Khz from DC).
- The birdies that are not a the same offset in the 1419
and 1667 band come from outside.
- Page 2: birdies strength vs azimuth
- PolA and polB have been averaged.
- Black is the CCW swing, Red is the CW spin
- top: 1419.963675 strength vs azimuth
- Bottom: 1667.957345 rfi vs azimuth
Summary:
- rfi was seen at:
- 1419.963675 MHz
- 1667.957345 MHz
- Using the anritsu spectrum analyzer with 3 Hz
resolution,
- the birdies were not resolved.
- the birdies move around by 20-50 Hz.
- There is not any obvious azimuth dependence of either
birdie
- The must be on the azimuth arm.
processing:
x101/130509/lbw1200.pro, lbwa2761.pro
28may13: 1419 birdie vs za
On 28may13 the 1419.963 MHz birdie
strength was measured vs za. the setup and processing
was:
- az=285, za 2.0 -> 19.0 at .02 deg/sec followed by
19->2.deg at -.02 deg/sec
- interim correlator with 190 hz resolution
- The peak value for the 3 channels about 1419.9638
was taken for each 1 second sample
- the median value of +/- 20 channels about the birdie were
subtracted
- The median value for all the baseline was used to
normalize to Tsys.
The plots show
the birdie
strength vs za (for az=285) (.ps) (
.pdf):
- black is moving up in za, red is moving down in za.
- The up and down passes overlay one another.
- The azimuth swings showed little az dependence
- This birdie was coming from the center of the bottom chord
of the azimuth arm
- The birdie got much stronger at high za.
- Another azimuth may have a different za dependence.
processing:
x101/130528/lbwbirdie.pro
