The plots show
the rfi from the system with the
cash register on and off (.ps) (
.pdf):
- Pages 1,2:
- each 100 Mhz band is plotted in a different color
- 0-3000 Mhz was split into 3 1000 GHz sections.
- For each pair of frames, the top frame is cash register
on and the lower frame is cash register off.
- For some freq ranges, there was more rfi in the off than
the on .
- Page 3: 100 Mhz blowups of 200-300,300-400,400-500 Mhz
- 200-300
- There is a 6.181Mhz comb that peaks at 245.83 Mhz.
- the strong birdie at 237.821 had harmonics at
475.9,713.385,951... 1426.77 Mhz
- has a harmonic at:k
A table of the strongest birdies:
freq
Mhz
|
amp
dbm
|
notes
|
237.821
|
-84
|
probably part of a
39.6457Mhz comb that is seen up to 1427.1651
|
245.83
|
-90
|
part of a 6.182 Mhz comb
|
327
receiver
|
317.06
|
-100
|
part of 39.6457 comb
|
|
475.825
|
-91
|
part of 39.6457 comb
|
1427.1651
|
-113
|
part of 39.6457 comb
|
1500
|
-97
|
|
processing: x101/rfi/miscdevice/eloCashReg_130306/cashdata.pro
22mar13: Emissions seen on the
telescope.
On 22mar13 the the emissions from the cash
register was measured on the telescope using the 327 receiver.
The setup was:
- 327 receiver used with center frequency at 317 Mhz.
- The cash register was placed in the middle of the patio in
front of the control room (where the scribe marks in the
concrete cross). It sat on top a small table (about 3 feet
off the ground).
- The telescope was positioned to az=333.2, za=17. Previous
az swings
showed this to be the peak azimuth for this position
(and the dome at za=17).
- The interim correlator was used with 1024 channels,
12.5Mhz bw, on second integrations, 9 level sampling, and
hanning smoothing.
- Data was taken for 300 seconds.
- The first 160 seconds had the cash register on, the
final 140 seconds had the power off to the cash register
After the datataking with the telescope, the
Rhode&Schwartz spectrum analyzer was used to measure the
field strength at the cash register. The setup was:
- preamp on, rms detector, 2 Mhz bandwidth, rbw=10Khz,
vbw=100 Khz (avg 10 sweeps), attenuation=0
- a 3 meter bnc cable connected the 904 Efield probe to the
spectrum analyzer.
- The probe was placed next to the strongest emissions from
the cash register (by the power cable connection to the
device).
A
dynamic spectra of the
300 seconds of data on the telescope was made (.gif):
- The dashed horizontal line shows where the power plug was
pulled from the cash register
- The birdie at 317.155 MHz disappeared at this point.
Average
plots of the cash
register on and off were also made (.ps) (
.pdf):
- Top Frame: Black: average (160 secs) cashReg on,
Red: average cash register off(140 secs). the dashed green
line is the birdie at 317.155
- 2nd Frame: On/off -1. This shows the birdie strength in
units of Tsys (about .008 Tsys).
- Bottom: Strength of the cash register emissions using the
Spectrum Analyzer and the 904 Efield probe.
- The probe was placed write next to where the power cord
connected to the device.
- The peak was -97dbm. It corresponds to the birdie seen
in the telescope.
- When the probe was moved away from the cash register,
the birdies disappeared (so it was not coming from some
other source).
processing:
x101/130322/rfitest.pro
Summary:
- Cash reg has very large rfi in 200-300 Mhz range.
- There are birdies seen up to sband.
- In our receiver bands the strongest birdies are:
- 327 = 317.155
- lband 1500 Mhz
- With the cash register sitting on the patio in front of
the control room, the 317.155 birdie was seen in a
24Khz bw, 1 second integration.
- A -97dbm birdie (10Khz rbw) seen with the 904 Efield probe
adjacent to the device can be seen in the telescope with a 1
sec, 24Khz bw when placed on the patio of the control room.
- This device can probably be used in the cafeteria (since
there is extra path loss).
- More tests should be done before this device is allowed at
the visitor center.