Only one pretty picture this time, folks. Take a walk outside to the
high bay and see the setup yourself... Beam maps were taken with
BICEP on the mount, staring across the high bay (about 50 meters) at
three different sources: chopped polarized LN2 thermal source
(a.k.a. the puppet theater), 100-GHz Gunn, and 150-GHz Gunn. All the
sources were chopped at about 2 Hz. Beam scans were taken by driving
the mount in azimuth and elevation. Encoders were working for both,
but we could only read one at a time with the daq. Thanks to Yuki,
Kiwon, and Darren for much data-taking support, and to John for
setting up the encoders.
|
Some quick notes on the organization of the plots... Most of the
files have 8 plots, corresponding to 2 source polarizations x 2 PSBs x
2 beam scans (az and el). The ordering changes between files, so read
the plot titles carefully if you want to compare signals. Unless
otherwise specified, the boresite was adjusted so that vertical source
polarization is roughly aligned with CP-b.
|
Thermal source measurements for CP (100 GHz) and
pixel A5 (150 GHz)
Bolometer signals were piped through an SRS preamp (gain 2-5, plus low
pass filtering) for these files. Thermal source wasn't properly
eccosorbed (is that a verb?) for this run, so the orthogonal PSB
response is rather high. Some of the fits aren't so great...there
seems to be some sort of time constant (thermal?) in the second half
of every beam pass. Also saw this with the Gunn sources; here's a
plot showing the signal drifts.
|
Gunn measurements for CP at 100
GHz, 96 GHz, and 104 GHz
Beam widths look fairly normal (predicted FWHM about 0.95 degrees).
We see a double lobe structure again...it appears in the bolometer
that's orthogonal to the source polarization, and is most prominent in
the 100-GHz scans. No double lobe structure in any other pixels.
|
Gunn measurements for CP,
boresite rotated 45 deg
Gunn is set for 100-GHz output. Not much else to say here.
|
Gunn measurements for pixel
A3 and pixel A5
A3 is an off-axis 100-GHz pixel; beams look good. A5 is a 150-GHz
pixel close to the center...we've confirmed that the combination of
Carlstrom oscillator + frequency doubler works for a 150-GHz source,
whee...
|
CP sidelobes (linear scale)
and log scale
Forget that low power stuff. For these measurements, we cranked up
the 100-GHz Gunn up to full power and put a horn on the end (all
previous measurements used Gunns blasting out of open-ended
rectangular waveguide). Main lobe squishing appears in copolar beams.
The bolometers that are orthogonal to the source polarization are a
better indicator of the sidelobe levels (signal ~ copolar response x
pol efficiency epsilon).
|
A5 high power Gunn measurements
We also tried high power measurements with the 150-GHz Gunn source,
but we didn't have a horn at our disposal. So alas, no sidelobes...
|
Some 100-GHz Gunn leakage, even at
lower power levels
These plots show raw undemodulated timestreams of the central pixel
and A5, a 150-GHz neighbor. The 100-GHz Gunn appears to be putting
out power in the 150 band.
|
A raster for John
Nope it's not a children's book, it's a plot. Nothing quantitative
here... The elevation angles are very approximate -- obtained
using an official BICEP marker-and-duct-tape encoder. Sorry for the
axis scale stretch; the beams aren't actually elliptical.
|
Take a psych quiz
|
|
Az scan, | pol |
Az scan, -- pol |
El scan, | pol |
El scan, -- pol |
| Thermal, CP-b / CP-f |
0.43 / 0.45 |
0.49 / 0.44 |
0.41 / 0.66 |
0.56 / 0.42 |
| 100-GHz Gunn, CP-b / CP-f |
0.35 / - |
- / 0.39 |
0.40 / - |
0.36 / 0.38 |
| 96-GHz Gunn, CP-b / CP-f |
0.38 / 0.38 |
0.38 / 0.38 |
0.37 / 0.45 |
0.38 / 0.39 |
| 104-GHz Gunn, CP-b / CP-f |
0.37 / - |
- / 0.38 |
0.40 / - |
0.41 / 0.37 |
| Boresite 45 deg, CP-b / CP-f |
0.37 / 0.35 |
0.48 / 0.42 |
0.49 / 0.46 |
0.35 / 0.33 |
| 100-GHz Gunn, A3-b / A3-f |
0.37 / 0.38 |
0.38 / 0.37 |
0.37 / 0.43 |
0.37 / 0.38 |
| Thermal, A5-f / A5-b |
0.29 / 0.31 |
0.38 / 0.28 |
0.27 / 0.32 |
0.39 / 0.28 |
| 150-GHz Gunn, A5-f / A5-b |
0.27 / 0.31 |
0.31 / 0.28 |
0.28 / 0.24 |
- / 0.27 |
|
ZEMAX-predicted beam widths for central pixel: 100 GHz, FWHM 0.95 deg
= sigma 0.40 deg ; 150 GHz, FWHM 0.63 deg = sigma 0.27 deg
|
Only one pretty picture this time, folks. Take a walk outside to the
high bay and see the setup yourself... Beam maps were taken with
BICEP on the mount, staring across the high bay (about 50 meters) at
three different sources: chopped polarized LN2 thermal source
(a.k.a. the puppet theater), 100-GHz Gunn, and 150-GHz Gunn. All the
sources were chopped at about 2 Hz. Beam scans were taken by driving
the mount in azimuth and elevation. Encoders were working for both,
but we could only read one at a time with the daq. Thanks to Yuki,
Kiwon, and Darren for much data-taking support, and to John for
setting up the encoders.