Birdies with 1 minute period in 430 and 327.
last updated 02jun06
29may/12feb06: 430 yagi/linefeed have 1 minute
02dec05: birdies at 430 Mhz with 1 minute
28oct05: azimuth swings at 327 Mhz show
birdies with 1 minute periodicity.
Time varying birdies are seen at 430 and 327 Mhz. At 430 they are
seen in the dome, carriage house, and the 430 Mhz yagi. It was 5 times
stronger in the 430 yagi than the 430 linefeed.
At 1 frequency the birdie repeats every 60 seconds.
The duration of the birides is 2.31 seconds.
At 430 Mhz there is a pattern of 4 frequencies that are staggered in time.
This pattern of 4 frequencies is repeated about every 7 Mhz. At 327
Mhz it looks like there is a single set of 4 frequencies staggered in time.
At 430 MHz the 4 birdies occur at : 7.5, 20.5, 33.6, and 41.1 seconds after
the minute. Measurements taken in 12feb06 and 29may06 showed the 20.5 second
birdie at the same phase of the minute. Whatever is creating the birdie
is locked to some clock.
The frequency separation of the 4 frequencies at 430 differs from that
The 327 birdies show an azimuth dependence. (no azimuth swings were done
at 430 ). They appear at azimuths 80 thru 180. They are strongest around
azimuths 113 and 147 in the dome 327 receiver. Azimuth dependence
means the birdies are coming from outside the dome.
The birdie power gets up to 5*Tsys in a single 24 Khz channel.
Crosses were done on continuum sources with the 430
Mhz yagi for calibration. The data was taken on 12feb06 and 29may06.
On both dates, positive jumps were seen on the total power output.
29may06/12feb06 430 yagi
has large 1 minute glitches
The data was taken in continuum mode with a 1 Mhz
bandwidth centered at 430 Mhz. A time constant of 20 milliseconds was used
with a sampling rate of 100 Hz. Each leg of the cross lasted for 90 seconds
(1 in az, 1 in za). It took 30 seconds to move between the az and za leg.
Crosses were also taken with the linefeed for calibration cross reference.
At first we thought the jumps were a problem with
water in the hybrid that converts linear to circular. After plotting the
data versus wall time (rather than position along the strip) a 1 minute
periodicity was seen. The plots how the results of the measurements:
yagi glitches (.ps) (.pdf):
linefeed glitches (.ps) (.pdf):
Top: Total power for a single cross versus wall time (from start
of observation). The first set is the az strip, the second is the za strip.
The red dotted line flags a jump that occurs every 60 seconds.
Bottom: (Total Power - beam fit) vs AstTime module 60 seconds for
all 24 yagi crosses. There is a jump that starts at 20.5 seconds after
the minute and lasts for 2.31 seconds. The horizontal scale was blown up
to 10-30 seconds, but there were no other visible jumps in the 60 second
time span. The jumps are about 15 kelvins.
yagi glitches (.ps) (.pdf):
Cross #2 for the line feed. The top is versus seconds from start
of observation and the bottom is AST time modulo 60 seconds. You can see
the jump at 20.5 seconds after the minute in the linefeed data. It is about
linefeed glitches (.ps) (.pdf):
The top plot has two crosses plotted versus time from the start of the
observation. There are 4 colored dashed lines then align with the first
4 jumps. They are then repeated every 60 seconds. All of the other glitches
line up with one of these 4 combs. The bottom plot is power-fit vs ASTseconds
modulo 60 seconds. All 10 yagi crosses are shown. There are 4 separate
jumps that align with : 7.5, 20.5, 33.6, and 41.1 seconds after
the AST minute. The jumps are 20 to 25 kelvins.
The second cross is plotted vs start of observation (top) , and versus
AST seconds modulo 60 (bottom). The 4 60 second combs found in the yagi
data are over plotted in the linefeed data. You can see the jumps at 7
seconds and 20 seconds (the other two are on the slopes of the beam and
are hard to see). The size of the jump is about 5 kelvins.
The 430 yagi has strong 1 minute glitches.
On 12feb06 there are 4 separate phases for the 1 minute glitches. The 1
Mhz bandwidth taken about 430 Mhz includes 4 of the 1 minute glitch frequencies
found in the dome: 429.89, 430.31, 430.39, 430.48. Each of these had a
The glitches are also seen in the line feed but they are about 5 times
The phase of the 1 minute glitches are: 7.5, 20.5, 33.6, and 41.1 seconds
after the start of each minute. The phase for the 20.5 glitch was the same
on 12feb06 and 29may06 (a span of 3.5 months). Whatever is causing the
rfi is stable in time.
The rfi glitch lasts for 2.31 seconds.
02dec05: birdies at 430 Mhz with 1
minute periods. (top)
Project A2125 was doing mapping at 430 Mhz. The data
showed some time dependent birdies. On 02dec05 i took some data with the
interim correlator and the 430 dome receiver. The setup was:
The plots show the birdies seen during this session:
25 Mhz bw, 2048 channels, 1 sec dumps, cfr of 430.
Data was taken for about 2 hours while sitting at az=270, za=10.
spectra for 300 seconds, polA (.gif): This image is spectral density
(time vs freq). The small dots are the time variable rfi. The short lines
at the bottom of the plot are added to show where these birdies occur (some
of the weaker periodic birdies were not flagged).
and frequency extent of birdies (.ps) (.pdf):
The top plot shows the power in the 429.89 Mhz birdie vs time. It lasts
for 3 samples so the time duration of the signal is about 2 seconds. The
bottom plot shows a spectral blowup of this same birdie. The freq. resolution
(after hanning smoothing) is 24 Khz. The fwhm is about 3.5 channels so
the birdie is about 30 khz wide.
periodicity of channels over 1500 seconds (.gif): The spectra from
the first 1500 seconds of data was interpolated in time and then
fft'd along the time direction. The image shows periodicity vs Rf frequency.
The vertical scale is in milliHz. The horizontal dashed lines are plotted
ever 16.66 milliHz (1/60. seconds). You can see strong periodic combs
around 422-423 Mhz, 430 Mhz, and 432.5 Mhz. These channels have birdies
that have a 1 minute period. There are also some channels that have a weaker
1 minute periodicity (but do not show up well in this image).
power vs time for 140 minutes (.ps) (.pdf):
Thirteen freq. channels with 1 minute periodicity were selected. The power
in the channels were averaged over 7 freq. channels and then plotted versus
Fig 1: all 140 minutes. Each color is a different birdie. The top plot
is polA while the bottom plot is polB. This data taking session started
at about 9 am. You can see that the birdies were stronger at the beginning
of the run. Looking at the data toward the end of the run, the periodic
birdies were still seen at some of the frequencies. The gaps in the data
are where no data was taken (between scans).
Fig 2: This is a blowup in time of fig 1 showing the first 5 minutes of
data. The dotted lines in polA (top) show how the birdies are aligned in
time. You can see two groups. The first starts at 422.72 (lower black trace)
while the second group starts at 429.89 (light blue middle trace). The
nth birdie of each group occurs at the same time.
Fig 3: (power in periodicity) vs period: For each birdie, 8500 seconds
of data was interpolated and then fft'd. The plot shows the power vs periodicity.
There is a comb with 16.6 millihz spacing (1/60 seconds). The width of
the comb was 1 channel (about .1 millihz) so the 60 second period is relatively
Summary of 430 birdies:
||about 30 Khz
||about 2 seconds
||4 birdies per group
rf spacing: .45,.1 .1 .1 Mhz
tm spacing in group: 13,7,26 seconds
each group repeats every 60 seconds.
|group rf spacing
||7.2 Mhz between groups.
|422.72, 423.18, 423.25, 423.35 grp1
429.89, 430.31, 430.39, 430.48 grp2
||looking at the x111 data for oct/nov05 we had:
18oct05 : 2 scans worth of birdies
26nov05: birdies started to appear more regularly
On 30nov05 A2125 also saw a group of birdies
at 432 Mhz. The 7.2 Mhz spacing looks close to the comb that is generated
by the alfa motor controller. The 1 minute birdies are also seen
at 327 Mhz (see 327
dynamic spectra of 3rd az swing). The dots around 318.6 are spaced
by 1 minute (20 deg azimuth = 1 minute in the plots).These were done with
the alfa motor controller turned of.
On 28oct05 5 azimuth swings were done with the 327 receiver
to check the azimuth dependence of the birdies in the 327 receiver (see
327 azimuth spins).
28oct05 327 Mhz rcvr
azimuth swings show 1 min periods. (top)
The az swing dynamic spectra showed some birdies
that were coming and going with time. They were centered around 318.6 Mhz
and azimuth near 120 degrees (see the
az swing dynamic spectra 2,3,4,5). These dynamic spectra were made
with polA. The last 3 azimuth swings in polB turned out to have the
strongest ence of these birdies.
The plots show that there are 4 birdies with a time
variability of 1 minute. Plotting versus azimuth shows that the birdies
also have an azimuth dependence. This implies that they are coming
from outside the dome/azimuth arm. The spacing between the 4 frequencies
is different from that found at 430. The signal to noise and number of
groups is less than the 430 measuremnets (probably because we were swinging
the azimuth). Having 4 frequencies and a time dependence of 1 minute probably
says that the 327 birdies are coming from the same source as the 430 birdies.
spectra of the last 3 az swings (.gif): These are from polB. 2.5 Mhz
was taken from the larger 25 Mhz band. The spectra show:
The dots appear for azimuths 80 to 180. The repeatability shows a real
They tend to jump in frequency like the 430 Mhz birdies.
of the 4 birdie frequencies (.ps) (.pdf)
: The power in a single spectral channel was extracted and plotted.
The 4 birdie frequencies are: 318.41, 318.47, 318.56, and 318.74
Fig 1: 60 second periodicity of the birdies. The time of
each birdies is plotted modulo 60 seconds. The 3 plots are az swings
3,4,5 (polB). The 4 colors code the 4 frequencies. All of the birdies of
the same color line up modulo 60 seconds for the duration of all of the
az swings. For each az swing there are only one or two birdies of each
frequency that stick up (so it only lasts for 1 or two minutes while the
azimuth is moving).
Fig 2 top: 4 birdies versus time for the last azimuth swing.
The colors show the 4 birdies. The dotted lines are spaced by 1 minutes.
Fig 2 bottom: 4 birdies versus azimuth for the last 3 azswings.
There are peaks at az 113 and az 147. The birdies do not appear when we
move away from these azimuths.
Summary of the 327 birdies:
||about 30 khz
||peaks at az 113 and 147 degrees.
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