01/08aug06 4-6 ghz amp,cbh noise/gain
mmic amp, noise src, cbh using square law detectors.
28jul06 test 4-6 ghz amp in test dewar sample
Setup/processing of 08aug06 data: cbh
using the wapps.
Plotting the data: 1 second averages,
allen deviation, acfs.
Plotting the data: spectra.
The noise/gain stability of the various devices was
tested by fast sampling of the total power and then computing the allen
variance and the power series spectra. These tests are to see what the
switching speeds need to by for the continuum reciever where the switch
will be after the dewar.
01/08aug06 4-6 ghz amp,cbh
On 01aug06 the 4-6 Ghz mmic amp was tested as well
as a noise source and the cbh receiver (with the shutter closed).
This used a 500 Mhz bandwidths and square law detectors. This data showed
lots of 60 Hz.
On 08aug06 the cbh receiver was tested by
itself using the wapps and a 100 Mhz bandwidth.
mmic amp, noise src, cbh using square law detectors. (top)
The 4-6 Ghz mmic amplifier was set
in a dewar in the cryo lab. A 500 Mhz band was mixed down to a cfr of 500
Mhz and then sent to the control room where it was square law detected
with a 50 Usec time constant and then sampled at 25 usec. Data was taken
for about 42 minutes using the RI. 3 other bands were sampled simultaneously:
Setup/processing of 08aug06
data: cbh using the wapps.
The cbh with the shutter closed was used.
The wapps ran at 32 usec sampling, 3 levels, and 100 Mhz bw. Data
was taken for about 45 minutes. The 0 lag was 3 level corrected and then
used as the total power. The processing was the same as the 01aug05 data
(except that the maximum sample rate was 32 usecs rather than 25 usecs).
Plotting the 1 sec avgs, allen deviation, and acfs. (top)
1 sec averages, the allen deviation, acfs, no filtering (.ps)
1 sec averages, the allen deviation, acfs, with 60 hz removal (.ps)
1 sec averages, the allen deviation, acfs, using the wapps (.ps) (.pdf)
Top plot: 1 second averaged time series:
01aug06: cbhPolA (blue) had a jump around 100 seconds of .5%
Tsys and a glitch around 1900 seconds. The noise src had a negative drop
around 1900 seconds. I wonder if someone was moving the cables that went
to the ri?? The filtered and unfiltered data sets are the same.
08aug06 : The data shows a 512 second cycle of about 1% of Tsys.
This was not present on 01aug06. The turret room temperature was monotonically
increasing during the time period so it is not coming from the gregorian
dome. This data used the same amps in the downstairs IF/LO as the 01aug06
data (where the cycle was not seen). The analog unit of the wapps in the
clock room was different. Either the ac cycle was different on 01aug06
or the gain variation with temperature is in the wapp analog chassis.
Center plot: the allen deviation:
01aug06: The integrations times were 25 usecs to 50 secs. The purple
diagonal line is the expected rms for 2*integration times (since we subtracted
two points). The allen deviation shows:
The measured differences start out below the expected deviation. The difference
value for an average of 5 to10 agrees with the expected rms.
The unfiltered data has a maximum around 8 milliseconds (1/2 of a 60 hz
The unfiltered data again agrees with the expected rms when the integration
time is 50 milliseconds. The difference time is 100 milliseconds. This
is a multiple of 60 hz so the 60 hz component should cancel.
The filtered data agrees with the expected value up to about 50 milliseconds.
This shows that the bump at 8 milliseconds was from the 60 hz.
The test dewar has a peak around 250 milliseconds
and then drops off. This is probably from the strong .8 second cycle from
the cross head. The noise source (with no refrigerator) remains flat.
The cbh dewar rises but does not peak (it's thermal mass probably damps
out the refrigerator cycle).
cbhPolB rises slowly starting at .1 seconds. cbhPolA starts rising at 50
milliseconds and then remains flat. cbhpolB was taken with the square law
detectors in the left rack. They seem to work better than the ones in the
right (that cbhPolA used).
08aug06: The integration times are 32 useconds to 64 seconds. The
allen deviation shows:
The allen deviation is decreasing linearly (1/sqrt(time)) from 32 usecs
to about .16 seconds where it flattens out. At about 10 seconds it starts
to increase. There is little 60 hz nor 1.2 hz from the crosshead.
The measured rms is 1.47 times (about sqrt(2)) times larger than the expected
rms. I've included the factor of 1.23 for the 3 level sampling when computing
the expected rms. I'm not sure why the measured value is not closer to
the expected one. The counts in the 0 lag were close to the optimum values.
Bottom plot: acf of time series difference:
01aug06: The acf is non zero until about lag 5 (see the filtered
data). This explains why the first 3 allen variance measurements (1 deltaT,
2 deltaT, 5 deltaT) are lower than the longer integrations. The time
constant ( 50 usecs) rolled off slower than the sampling (25 usecs) leaving
adjacent samples with some correlation. The actual allen variance is probably
linear down to the 25 usecs differences.
08aug06: The time series from the wapps have no correlation all
the way down to lag1.
spectra of the time series no filtering (.ps) (.pdf):
plotting the spectra: (top)
spectra of the time series with 60 hz removal (.ps) (.pdf):
spectra of the time series using the wapps (.ps) (.pdf):
Top plot: 1 hz resolution. full bandwidth: The spectra have been
offset for plotting.
01aug06: 20 khz bandwidth, 64K length xforms. The filtered data
have negative going spikes at the 60 hz harmonics since this power was
removed. There is a spike around 8435 hz (118.5 usecs). It is not in cbhPolB
(which used the leftmost square law chassis) so the birdie is probably
coming from the square law chassis on the right. The power falls off with
frequency. This is probably being caused by the square law time constant.
The acf showed that the first few lags were non zero.
08aug06: 15.5 Khz bandwidth, 32K length xforms. The spectra is clean
except for a spike at 60hz. The spectra is also flat with frequency. It
does not fall with frequency like the 01aug05. The level is also higher.
It should be a factor of 2 higher since the transform length was 32K rather
2nd plot: 1 hz resolution blowup (0-2500 hz):
01aug06:The 60 hz on the test dewar has more harmonics than the
others. cbhPolB has the least 60 hz (it used the left square law chassis).
The filtered plots show the negative going spikes at 60 hz harmonics. The
test dewar has a few harmonics above the 960 hz filter cutoff. We looked
at the 60 hz on the scope and it is a square wave rather than a sine wave.
08aug06: There is 1 spike at 60 hz and 1 at 180 hz. This 60 hz is coming
from a sine wave rather than a square wave.
3rd plot: 1 hz resolution blowup ( 0-500 hz):
01aug06: The harmonics of 60 hz are flagged. cbhpolb has the
least 60 hz (square law detectors from left rack). The filtered version
is plotted on the same scale. It has very little 60 hz.
08aug06: There is a 60 hz and a 180 hz spike. Pol A is a little
stronger than polB.
bottom plot .05 hz resolution:
01aug06: 50 points were averaged and then a 16384 length xform
was done. You can see the strong 1.2 hz birdie from the cross head for
the test dewar. cbhPolA (blue) has a lot of junk from 0 to 1 hz with a
peak at .5 hz. This is also evident when you look at the 1 second average
time series. There is a lot stronger high frequency (.5 hz) noise in cbhPolA
than the other data sets. This is probably why the allen deviation for
chbpolA flattens out around .5 seconds.
08aug06: 75 points were averaged and then a 8192 length xform was
done. You don't see the 1.2 hz birdie from the crosshead. There is more
low frequency power caused by the gain cycling from the AC.
processing: x101/060801/ see Readme file for processing steps.
Square law detector data:
The 8 millisecond peak in the unfiltered allen deviation is coming
from 60 hz in the square law detectors.
The square law detector chassis on the right has more 60 hz hum than the
one on the left. It also has an 8.5 khz birdie. The 60 hz is a square
wave giving many harmonics. It's power supply should be looked at.
The second bump in the allen deviation around .25 seconds in the filtered
data set is coming from the 1.2 hz crosshead cycle.
The time constant in the square law detector has correlation's up to 4
times the nyquist sample frequency. This causes the allen deviation to
be smaller than expected for short integrations.
The allen deviation decreases as 1/sqrt(integTime) up to about 25
milliseconds integration time (looking at the filtered data).
The wapp data:
there is very little 60 hz.
The gain is changing by about 1% tsys on a 511 second cycle. This is probably
coming from the analog units of the wapps. A lot of on/off position switching
does a 5 minute on, 5 minute off, followed by a single cal. The cal assumes
that the gain has remained constant for the on and the off. It woud be
good to slow down the AC cycle some.
The allen deviation decreases as 1/sqrt(integTime) up to .1 second
integrations. The measured rms is about sqrt(2) larger than the expected
28jul06 test 4-6 ghz amp in test dewar. (top)
A new wide band mmic amplifier was tested on 28jul06.
A test dewar was running in the cryo lab. A 600 Mhz band of the amp was
mixed down to 500 Mhz and sent to the control room where it was detected
with a 20 usec time constant and then sampled at 10 usec with the ri.
The first plots show the
data samples and the allen deviation of the 28 minute data set (.ps)
The 2nd plots show the
spectra of the total power time series for the 1600 seconds of data (.ps)
Top: total power vs time. The total power samples were avg.
to 1 second and then plotted. They have been normalized to the average
total power value. The red dashed lines are the expected rms for a 600
Mhz 1 second integration. Looks like the total power jumped a bit
around 1200 and 1500 seconds.
Bottom: The black plot is the allen deviation. To compute this we:
Made n passes thru the data.
On each pass avg. a different number of adjacent points (1,2,5,10,50,100,200,500,1000,...)
After averaging, compute the difference of adjacent points and then compute
the rms of these differences. This is what is plotted in black
The green * are averages that are integral multiples of 60 hz.
The red line is the expected rms for a data set with 600 Mhz bandwidth
and avg*2 seconds (*2 since the subtraction of the adjacent points is the
same as averaging by a factor of two more).
top: The detected power was sampled at 10 useconds. This shows the
full 50 Khz averages over the 1600 seconds with about 1 second resolution.
2nd: Blowup of 0 to 3 Khz. Multiples of 60 hz have been flagged in red.
3rd: further blow of 0 to 500 hz. showing the first few multiples of 60
bottom: .064 hz resolution data 0 to 10 Hz. Multiples of 1.2 hz have been
flagged (the refrigerator cycle).
The allen deviation starts at the expected value but
diverges rapidly. This is probably from the 60 Hz. The points that are
integral multiples of 60 hz remain above the expected rms. This may be
the 1.2 hz refrigerator or some other drift.
The spectra shows lots of 60 Hz. This is probably
not too surprising since we ran a long cable from the cryo lab to the receiver
room. We probably should have ac coupled the system.