Intro
The Boston University (BU) all sky imager
is installed in the antenna test building (SE corner). It
consists of:
- A laptop
- A control module
- camera (mounted right beneath the ceiling)
- filter wheel
- tube, lenses going through the ceiling.
- tube going through the ceiling.
The imager has been installed and
running for some time (actual dates?). In jul16 one of the GPS
system users complained of interference at GPS (L2
1227.6). It was found that the BU imager was interfering with
it.
160809: measure rfi from imager in ant.
test building
On 160809 around 20:00 we went to the antenna
test shack to check the rfi from the BU imager.
T
he setup was:
- Anritsu spectrum analyzer with large loop antenna
- 3 mhz rbw, sweep from 0 to 2 GHz, preamp on, record in
peak hold mode. For each measurement we usually had at
least 10 sweeps across the band.
- We positioned the loop antenna perpendicular to the bottom
side of the camera body.
Measurement sequence:
- file 103: camera on
- file 104: camera off but power applied
- file 105: camera off , power removed
- We then turned the camera back on and moved the filter
wheel.
- file 106: camera off, but powered.
The plots show the measured
signal (.ps) (.pdf):
- Black traces: the 3 peak holds with the camera off.
- There was not a large difference between the camera off
and the camera powered off
- Red trace: Peak hold for camera on.
Summary:
- the spikes 480 to 700 MHz are tv stations.
- lots of Imager emissions from 600 to 1600 MHz (above that
the antenna my be dropping off).
- When the filter wheel was active, i occasionally saw large
narrow spikes between 500 and 1500 mhz.
- no record was made of this.. it was difficult to
separate this from the other junk going on.
- The datataking sequence they used has the camera making
rfi for 5 to 10 seconds, then it goes quite for a few
seconds.
- We should probably bring the entire device (controller,
camera, filter wheel, tube and lenses down to the screen
room so we can do a more thorough job of measuring the rfi.
- I'm not sure why this device was installed without first
being checked for rfi....
processing:
x101/160809/rfibuimager.pro