327 band RFI measurements.
last updated 08feb16
01jun17: rfi from
sband console in dome.
11oct16: az encoder rfi
measured in screen room.
turning the sband console on,off after removing external ups, power
4Mhz comb from sband console coming from ups outside of cabinet
29jan16: cleaning up the
327mhz band.. jan16
turning the sband console (upstairs) on,off after the cabinet
28jan16: turning the sband
console (upstairs) on and off.. before repairs.
fixing the shielding gasket on the turret control box (in the dome)
27jan16: probing the sband
console (upstairs) with the anritsu
25jan16: hi frequency
resolution azimuth swings
anritsu spectrum analyzer in the if/lo rack in the dome.
04mar14: 327 rfi from meteor camera on antenna
320-325 Mhz drifting birdie seen feb14
rfi seen in the p1693 pulsar search
P2717 327 incoherent search with puppi show avg spectra, rms, and
3rd harmonic of 102.9,104.1 with a dipole.
harmonics and intermods of fm 102.9,104.1 from route 10
screen room birdie strength to detectability on the telescope
elo touch screen cash register. Emissions in screen room and on
spectrum analyzer at building 2 a/c unit shows rfi.
24jan13: 327 rfi
when building 2 power cycled.
harmonics of fm stations 104.1,102.9 from route 10.
03nov11: possible 2 Mhz comb in 327 Mhz band.
03nov11: check alfa motor controller rfi after
shutdown of visitors center.
10aug11: short duration
broadband rfi seen by p2558 in the 327 rcvr.
salters list of rfi at 327,430 using telescope data.
tested compressor monitor on telescope 06jun11 using 327
02mar11: alfa motor, cameras, and distomat rfi.
09aug09: rfi from
11jun09: rfi from sband console/alfa motor.
created by axis 212 web camera.
and 40 Khz 327 combs come from the sband console in the dome.
39.45 Khz combs in 327 receiver
13apr06: testing the trenddata gigabit
switch for rfi.
ac units in dome. Compare with comb from old unit.
show birdies with 1 min periodicity
at Dome ac birdies in 327 Mhz rcvr.
fm stations appearing in band
filters before the 1st amp
327 Mhz band.
and their azimuth dependence.
21oct05: 327 Mhz spectral density
at output of 1st amplifier (before the rf filter)
in 327 receiver from both dome AC units
327 receiver from alfa motor.
03dec03 327 Mhz comb
from sband Tx Rack in dome
24nov03 comb at 327 Mhz.
24jul02 2 MHz comb in 327 Mhz
01dec03 327 Mhz comb coming from sb Tx
room in dome.
04mar14: meteor camera rfi
The meteor camera atop the old antenna test shack
was found to make rfi at 324 Mhz.
We turned the camera off around 16:07 04mar14.
p1693 was taking 327 drift data when we did this:
The dynamic spectra shows the
data during the turn off (.gif)
- 327 Mhz receiver, mock spectrometer, 55 Khz channel width,
- az=332.0831, za=11.0675 (during the cable repair)
You can also see this in
the 04mar14 dynamic spectra for p1693. (in this image it
occurs at 16.75)
- The spectra were averaged to 1 second
- I removed the median baseline, and gain corrected each spectra
by averaging over 343.128 to 348.728.
03nov11: possible 2Mhz comb in
A 110 second median spectra was taken with the
327 Mhz receiver. The setup and processing was:
The plots show the spectra for
the 110 second integration (.ps) (.pdf):
- 327 rcvr centered at 327 Mhz with the 302 to 352 Mhz filter
- mock spectrometer with 6.9 Khz resolution was used.
- alfa motor contoller off. dome cameras on.
- a 50 term harmonic was fit to the average spectra and then
used to bandpass correct it. 1. was then subtracted.
- PolA and polB were then averaged.
- The plots were split up into 10 Mhz sections with .5 Mhz
- The solid red lines at the bottom of each plot are
spaced every 2 Mhz on the even Mhz.
- The solid green lines are birdies close to 2 Mhz multiples
that show an azimuth dependence, measured
- Each of the green flagged birdies has a different azimuth
dependence, so they are not coming from the same source.
- They are located at:
- There are still a number of 2 Mhz multiples that have a red
flagged birdie present. It is also possible that the green
flagged birdies are hiding a weaker 2 Mhz birdie
that could be part of the comb.
03nov11: alfamotor (top)
The alfa motor cables had extra shielding added
when alfa was in the lab during sep11. on 03nov11 an rfi
test was done with the 327 rcvr to check the rfi being emitted by
the alfa motor controller. The setup was:
The dynamic spectra show the spectral density vs time:
- The 327 receiver was centered at 327 MHz with the 302 to 352
Mhz filter installed.
- The mock spectrometer was used with a 57 Mhz bw and 8192
channels (6.9 Khz resolution). Data was dumped at 1 second
- The on,off sequence for the alfa motor controller was:
- 0 to 65 seconds - motor on
- 65 to 158 seconds - motor off
- 158 to 213 seconds - motor on
- 213 to end motor off
- The horizontal dashed lines show where the motor was turned
- PolA entire band
- This has been smoothed,decimated to 43 khz channel
- 300.538 Mhz: solid rfi from 0 to 65 seconds. Goes away when
motor turned off
- 302.85 to 301.62 . Drifting birdie that occurs at 158
seconds when motor turned back on. Disappears when motor
- PolB entire band
(.gif) . Smoothed decimated to 64 Khz channel resolution.
- No obvious rfi from motor controller in polB.
- PolA blowup
around rfi with 6.9 Khz resolution.
- You can more clearly see the 300.538 Mhz birdie as well as
the drifting birdie when it was turned back on.
- Shielding the alfa motor controller has gotten rid of many of
the birdies seen back in 02mar11.
- A birdie is still present near 300 Mhz.
- This is probably part of the 10 Mhz comb seen back on
- When the controller is turned on a birdie appears at 302.85
Mhz and drifts down toward 300 Mhz.
- Since rfi is still seen from the alfa motor controller it
should still be left off during 327 and probably 430 Mhz
02mar11: alfamotor,cameras, distomat
On 02mar11 test were made to check the rfi from
the alfa motor controller as well as the dome cameras.
The setup was:
The dynamic spectra
shows the rfi vs time (.gif)
- 327 rcvr centered at 327 Mhz and the 302 to 352 Mhz filter
(this may actually be a straight thru connection).
- mock spectrometer with 57 Mhz bandwidth, 1 second dumps.
- Data was taken for about 400 seconds.During this time the alfa
motor controller was turned off, on a few times. The dome
cameras were also turned off and then on.
The plots show the
average spectra for the on and offs (.ps) (.pdf):
- The image has been bandpass corrected with the median value
for the 410 seconds.
- Any constant birdies will not show up.
- The horizontal dashed lines show where the devices were turned
on and off
|alfa motor on
|alfa motor off
|alfa motor on
|alfa motor off
- there is a 10 Mhz comb: 300,310,320,330 coming from the alfa
- There is a 7.5 Mhz comb that drifts to lower frequency when
the alfa motor controller turned on.
- the cameras have a comb at 14.3 Mhz spacing
- the 315 Mhz rfi at 200 and 320 seconds
- has pair of rfi spaced by 70 Khz
- spaced in time by 120 seconds
- This is coming from the distomats
- Each plot has been normalized by a harmonic fit to the median
bandpass during the off.
- Constant birdies (in the on and off) will remain).
- The vertical scale is tsys units.
- Page 1: alfa motor off (black) and alfa motor on (red)
- Top is polA, bottom is polB
- The off has been shifted left by -.05 Mhz so you can see if
the on and off's overlay each other.
- Page 2: cameras off (black) and cameras on (red)
- top polA, bottom PolB
- The green lines show the 3 camera birdies at 315.0, 329.30
(weaker), and 343.64
- The alfa motor controller is making rfi at 327 Mhz
- There is a 10 MHz comb: 300, 310... 350.
- There is a 7.5 Mhz comb that drifts to lower frequency when
the device is powered up
- The dome cameras are making rfi at: 315,329.30,343.64 (343.64
is the strongest) (14.3 Mhz comb)
- The distomats are make rfi at 315. Mhz.
11jun09: rfi from sband console, alfa
A strong comb was seen in the 327 rcvr around the
end of may09. It had a 750 Khz spacing which pointed to the sband
console. Data was taken on 01jun09 while various equipment was
turned on/off. The setup was:
The sequence of equipment on off was (by record
- 327 receiver
- interim correlator with 25 Mhz Bw centered at 320 Mhz with
- 1 second dumps for 1350 seconds.
- az,za set at :285,11.
The dynamic spectra for the
sequence is shown in the img (.gif) :
- 0 all on
- 155: cameras in dome turned off
- 318: alfa motor turned off
- 421: sband console breaker turned off
- 483: sband console breaker back on
- 1150: sband breaker off
- 1196: cameras back on
- 1277: alfa motor back on.
The next plot shows a spectral
average of the sband console on and off (.ps) (.pdf) :
- It looks like cameras off make a big difference at rec 155,
but the rfi did not come back when the cameras were turned on at
rec 1187 so it was probably just a coincidence
- at 318 the alfa motor was turned off and the drifting
birdie at 324.5 disappeared. When the motor was turned back on
at rec 1277, a 7 Mhz comb appeared at 315. It drifted rapidly.
- 421-483: turning off the sband console breaker got rid of the
750 Khz comb.
- Top: spectral average of records 532-1132 with the sband
console on. The vertical scale is tsys units.
- Bottom: blow up of spectral average with sb console on (black)
and sb console off (red). The green vertical lines show the
location of the sband console comb.
- The 320 Mhz birdie was still there when the console was
turned off so it was not coming from the sband console.
- The strongest comb element was 312 Mhz. It had a strength of
4*Tsys in a channel width of 24Khz (after hanning smoothing).
11jun09: after shielding the console:
Victor and rey worked on shielding the sband
console after this data was taken. A second test was done on 11jun09
to see the results. The setup was:
The image shows the 327 dynamic
spectra while the sb console was turned on/off (.gif):
- az,za set to 190,11.
- mock spectrometer used with a bw of 34 Mhz centered at 327
using 8K channels and .1 second dumps.
- the sband breaker was switched on/off. the record numbers
- rec 0: off
- rec 50: on
- rec 102:off
- rec 150: on
- rec 205: off
- rec 254: on
- The data processing averaged to 1 second and decimated the
spectra to 1024 take a peak hold within the 8 decimated
- There is no obvious on/off seen when the sband breaker is
thrown.. So the shielding must have corrected the problem.
- The 750 Khz comb from the sband console was removed after the
shielding of the cabinet was upgraded.
- The alfa motor controller is still generating birdies at 327
13apr06: testing the trenddata
gigabit switch for rfi. (top)
A trend data gigabit Ethernet switch (teg-s41sx)
was tested for rfi. This switch has 1 fiber port and 4 copper ports.
During the testing there was nothing connected to the switch (except
the power). In the screened room rfi was seen from the switch beyond
2 Ghz. The strongest birdie was at 476 Mhz. It was stronger than 50
db above the noise floor of thesbt250
spectrum analyzer (the resolution bandwidth was about 300 hz).
On 13apr06 data was taken with the 327 receiver
on the telescope and the interim correlator. The switch was located
in the parking lot next to the control room inside the rfi van. It
had a clear shot to the telescope through the front window or the
van. The azimuth was positioned to az=242, za=18 (the 1400
Mhz birdie from the wapps is a maximum here). The correlator
was set to 390 Khz bandwidth and 2048 channels. After hanning
smoothing the resolution bandwidth was 380 hz. 180 1 second
integrations were made.
The data taking started with the switch on. It
was turned off at second 80. It was turned back on at second 125. It
was shut off again at second 166.
- The first image (polA) shows the
for the 180 seconds (.gif).
- The birdie is at 335.9367 hz. You can see it come and go as
we switched the switch on and off.
- The majority of the other birdies are a comb with a
spacing of 39.5 Khz
- The second image is a 50
on the birdie (.gif):
- A plot of the
second spectra as well as the total power of the birdie
channel (.ps) (.pdf):
- The top frame overplays the 180 1 second spectra (with an
offset for plotting). There is a drift of about 1 channel (380
hz) in the spectra. It is probably a thermal shift when the
switch is off and then turned back on.
- The bottom frame plots the birdie channel (average of 2
channels about the peak). The black plot is polA while the red
plot is polB. The times when the switch was turned on and off
are flagged. Pol A is stronger than polB. The strongest is
about 11 times Tsys in an 380 hz channel width. Tsys for the
327 receiver is about 120 K.
- The gigabit switch with no link active makes rfi through
- The majority of the rfi is coming from the fiber to copper
- The strongest rfi is at 476 Mhz. It is 50 db above a 700 K
noise floor in 300 Hz resolution bandwidth when a probe is set
on the device.
- When the switch is placed in the parking lot next to the
control room, a birdie at 335.9367 Mhz can be seen in the 327
receiver. It is 11 times tsys in a 380 Hz channel. It was
stronger in polA than in polB. This was the strongest birdie in
the 327 Mhz band when looking at the switch in the screened
21oct05: 327 Mhz spectral
density at output of 1st amplifier (before the rf filter). (top)
The output of the 327 Mhz receiver after the
first amplifier was measured with the Tektronix ybt250 portable
spectrum analyzer. The signal was taken after the first amp
and before the rf filter (the filter limits the band to 30 Mhz about
325 Mhz). The telescope was at an az of 270 and a za of 8.46
degrees. Data was taken covering 0 to 1000 Mhz and then 0 to 500
Mhz. At each band a regular sweep and a peak hold of about 1 minute
were recorded. This was done for polA and polB. The plots show that
largest signals in the receiver band (.ps) (.pdf):
On 20oct05 we saw intermittent
intermods/harmonics in the 327 Mhz band that included the fm station
107.3 (3rd harmonic at 322) and intermods with a tv station
and 107.3 (we heard the fm station in the IF signal). The
power levels measured above do not look like they should be driving
the first amp into compression.
- Top: this covers 30 Mhz to 1000 Mhz. The black and red are the
single sweeps for polA and polB. The green and blue are the one
minute peak holds for polA and polB. The largest birdie in the
band is 471.25. This is the video carrier for tv channel 14. The
next two largest birdies are 519.25 (tv channel 22) and 187.25
(tv channel 9).
- Bottom: the 30 Mhz to 500 Mhz measurements.
The 1 minute peak hold has values that are up to
10 db stronger than the single sweep values so the levels are time
variable. There is most likely an azimuth dependence to the birdies.
It still looks like a good idea to put an rf filter before the first
amplifier (since the receiver isn't cooled).
327 Mhz comb from sband Tx Rack in dome. (top)
The 327 Mhz comb
(with 372 kHz spacing) is coming from the sband transmitter cabinet
in the dome. Rey velez noted that the fingers for making contact
between the door and the cabinet were not working. Data was taken
with the correlator while the sband rack was on and off. 1 second
dumps were done using a 24 kHz resolution and a 190 Hz resolution
(after hanning smoothing). A bandpass correction was fit to an
average of the band passes when the rack was powered off. The plots
show the 327
comb when the sband rack was power on and off. The door from
the sband transmitter room to the stairwell was open during these
- Fig 1 . A 30 second average with the rack on. The top plot has
24 kHz resolution while the bottom plot has 190 Hz. The vertical
units are Tsys.
- Fig 2. The 30 second average with the rack on (black) followed
by a 30 second integration when the rack was off (red). The top
plot has 24 kHz resolution while the bottom plot has 190 Hz. You
can see that turning the rack on created many birdies and it
raised the entire continuum level by about 10%.
24nov03 comb at 327 Mhz.
(note: this comb is coming from the sb tx console in the dome)
A comb appeared at 327 Mhz sometime in oct or nov03. Data was taken
on 24nov03 with the interim correlator using a 25 Mhz bw, 2048
channels, 1 second sampling, and centered at 327 MHz. An az swing
was done from az=290 (za=10) clockwise to an az at 660 using a rate
of .4 deg/sec. The az was then swung counter clockwise from 660 to
about 540 (where is stopped because the cable car was in use). The
plots show the
comb at 327 Mhz:
The comb spacing is 372 kHz with the strongest values at 745
Khz (actually 371.97Khz generates the comb at 327 MHz). There is
variation in the power for each element vs azimuth but it does not
look like something that would be coming from a tower far away. The
dropouts and increases do not repeat with azimuth implying that they
are a time variation rather than an azimuth dependence. The birdie
is probably on the platform or even in the dome. It would be
interesting to take some data with the doors to the turret room open
and then closed.
- Fig 1 Top is the average of the clockwise spin. Black
is polA, Red is polB. The units are Tsys (about)...Bottom:
This is the average of the counter clockwise spin. The vertical
scale is blown up to show the smaller birdies.
- Fig 2 This shows the spacing between the birdies. A
baseline was fit to the non-comb values and then removed. All
measurements above 1.5 Tsys were flagged as comb members. Combs
in adjacent freq channels were collapsed to the channel with the
largest value. The frequency difference was then computed
between all of the adjacent comb members. The data was plotted
with the comb intensity versus the comb frequency step. The
points clustered at multiples of 372 Khz with the largest number
occurring at 327*2=745 Khz. Black is polA, Red is polB, and
green lines are multiples of 372 kHz. The top plot is the
clockwise spin, the bottom plot is the counter clockwise spin.
- Fig 3: This is the strength of each comb element vs
azimuth position for all of the comb members found. The top plot
is the clockwise spin, the bottom plot is the counter clockwise
spin. Colors differentiate different comb members (note that the
colors on the top plot do not necessarily correspond to the same
frequency for that color on the bottom plot).
24jul02 2 MHz comb in 327
Mhz receiver (resolved). (top)
A 2 Mhz comb was found in the 327 Mhz receiver. It is at the
odd Mhz 327,329,331,.. Mhz. It is offset from the Mhz by
+3.737Khz. Looking more carefully you can also see a birdie offset
by the same amount at 326,328,330,.... The comb must be a 1 Mhz
square wave with the even harmonics non-zero because of
imperfections in the square wave. The birdie goes away when the
receiver is put on load so it is coming in through the front end.
The first lo was shifted and the comb remained at the same rf
frequency so it is not coming in after the first mixer.
Data was taken with the correlator in
195Khz/2048 channels (with hanning smoothing). This has a 190 hz
resolution. Band passes were centered at 327,329,331,and 333
Mhz. 1200 records were then taken while various devices were
turned on/off and doors opened, closed.
The 327 MHz birdie was then mixed down close to
base band and sampled with the radar interface at 10 Khz. This
measured the width and drift rate of the signal.
The plots show the results of these measurements (note.. the plots
call it a 2 MHz comb since the odd harmonics were so much
and 333 MHz The comb is offset 3.737 Khz
above 327,329,331,333, etc. The spacing is 2 Mhz within the
at 327 Mhz. The for the 157 seconds of the
measurement the signal drifted at .041 hz/second. At 327 Mhz
this is a stability of .041/327e6= 1.25e-10 fractional
change/second. 3.2 seconds of data were taken for each spectra
giving a resolution of .3 hz. It has still not been resolved
in the last spectra.
- Data was taken for 1200 seconds using the correlator. During
this time the doors going out to the stairwell were opened and
closed a few times. The doors to the iflo racks were also
opened and closed. The plot shows the birdie
-Tsys versus time for the 1200 seconds. The only
thing that correlates is the opening and closing of the outer
doors. Opening and closing the iflo racks did not make a large
Conducting gasket in huffman box degrades with time.
After turning off a number of equipment it was
found that the birdie was coming from the power meter that is used
to measure the power in the 430 Mhz wave guide. It is located on the
ceiling of the turret room inside a huffman box. It has an rf cable
going to it from the wave guide, a fiber optic cable sending the
signal downstairs, and an ac power code that goes through an ac
power filter at the input. Inside the box is a pc card with a
VtoF converter on it. This card uses a 1 Mhz crystal. There is
another of these boxes in the carriage house measuring the 430
Mhz output power. At first the ac power filter was suspected as the
culprit. The box in the carriage house was brought down and tested.
The main problem was the conducting gasket around the inside top of
the huffman box. It was supposed to improve the contact between the
top and the box when the top was closed. The gasket was a rubber
(neoprene?) material with a conductive coating. Where the gasket was
in contact with the box (top or bottom) the gasket was still
conducting. The edge of the gasket had a dark strip which was no
longer conducting so the top of the gasket was no longer
electrically in contact with the bottom. When the box was closed the
gasket was acting as an insulator for the top. The guess is that the
part of the gasket in contact with the air oxidized the conducting
material. This is a serious problem since most of the huffman boxes
we have use this gasket material. It is probably why the color
camera birdie was not there when the cameras were installed in their
new shielded boxes and then reappeared 6 months later.
01dec03 327 Mhz comb coming from
sb Tx room in dome.
On 01dec03 data was taken with the 327
receiver while tracking blank sky. The correlator was set for 2048
channels over 25 MHz (centered at 327 MHz) and 2048 channels over
195 kHz (centered at 321.7 Mhz. The data was dumped at 1 second
intervals and hanning smoothed to give resolutions of 24 kHz and 190
Hz. While the data was being taken, the doors to the sband
transmitter room was opened and closed as well as the door to the
turret room. Data was taken for 2200 seconds.
We knew that the signal was coming in through the
horn (since it went away when put on load). The doors should give
some shielding to birdies generated inside the rooms. If the birdie
strength increased when the door was opened, then it was probably
coming from inside the room. The plots shows the
327 comb data while the room doors where opened and closed.
- Fig 1 This is the average of the 2200 seconds of data. Black
is polA and red is polB (polB has been offset in frequency by a
few channels for display). The top plot is the 25 MHz band (24
kHz resolution while the bottom plot is the 195 kHz band (190 Hz
resolution). The 190 hz resolution data did not resolve the
- Fig 2. This is the time series for the 321.75 Mhz, 190 Hz wide
channel. The top plot is the entire 2200 seconds (it took me
awhile to get up to the dome to open/close the doors). The
bottom plot is a blowup of 300 seconds when the transmitter room
doors were opened/closed twice. The dashed green line is when
the transmitter door was opened. The blue line is when the door
was closed. (these times could have been off by a few seconds.
You can see that the power in the channel went up by almost a
factor of 7. This shows that the comb is coming from inside the
The dip at 1250 seconds is when i opened the
door rapidly and then closed it to get into the room for the first
time. When I closed the door, it must have made better contact