Summary of 74 MHz Test with Power Down at Parkes Site 20030129

1

• Summary of 74 MHz Test with Power Down at
  Parkes Site (2003-01-29)
• New Data file 2003-01-29_1120_z20s.rpf
  (apparently no matched load data taken this time)
• Matched Load Data for passband comparison was
  taken at an earlier session (2003-01-09)
• OVERVIEW CONCERNS
• Still pretty cluttered up with indications of
  spurious intermods being cycled in
• frequency with 25 minute cycle
• Strongest RFI spikes at 2048, 4096, 6144 (and
  some intermediate at N1024). Is
• correlator in good health?
• Total power passband on sky is much different
  than the passband with matched load
• (is the feed working right? We have been
  using the MITEC amps, and maybe Bills
• amps did more in the way of matching?)
• Description of Plots (that follow)
• 1. Comparison of spectra for one 5 second
  integration with scan average passband shape
• for a long integration on a previous date.
• 2. Total power versus time. Black lines are
  straight averages over frequency red lines

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Description of Plots (continued) 4. Dynamic
spectra First 50 minutes. Upper image is the
low frequency half of the band 72-74 MHz
lower image is upper half 74-76 MHz. A passband
shape was divided out the passband was
constructed by (1) median filtering each spectrum
in frequency, (2) skipping those that
jumped by 3 in total power, (3) averaging the
spectra from the time step range 20 to 6000
(during which they appear to be well
behaved in total power). 5. Dynamic
spectra 50 minutes near center of the
recording. 6. Dynamic spectra the entire range
of the recording. Only 1 in 20 spectra are
included. Note sawtooths gentle arcs. The
total power doubles during the recording
so that a smoothly varying total power level was
subtracted to keep the image values within
a useful grey scale But the noise level
increases with time through the image, and
the passband calibration becomes inaccurate,
since the sky power experiences a different
passband than the amplifier/ground-pickup
noise power (causing the white patches in the
extreme freq channels at late times). 7. Example
spectrum Normalized to Tsys1.0. Strongest
spikes at N2048 at 35 Tsys 8. Example
spectrum Normalized to Tsys1.0. Different
gains and zooms. Lower panels show channels
20494096 (left) and 40976144 (right). Looks
like N1024 and possibly some N512 coming
through.
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• Description of Plots (continued)
• Comparison Total Power vs. Time for site-powered
  (2003-01-09) and site-unpowered
• (2003-01-20).
• 10. 11. Dynamic spectra comparison of
  Site-Powered and Site-Unpowered on
• same stretch (normalized to unity Tsys).
  The other possibly important influence on the
• appearance of the dynamic spectra is whether
  the Parkes dish is allowed to move or
• not. When it changes its position with
  respect to the 74MHz feed (which is sitting
• on the ground), the reflected ground/sky
  radiation changes, and the total power and
• passband shape changes. This is probably the
  cause of the bright and dark bands in the
• image for 2003-01-09. The other possibility
  could be a time-variable source of
• broadband noise.
• 12. Comparison of Spectra from averages Time
  Steps 15002099 (Galactic Pole) and
• 50005599 (elevated total power as creep into
  Plane) Galactic Center transited during
• the daytime, and RFI levels became
  prohibitive.
• Difference between spectra in Fig 12. This is
  the Gain(f) curve.
• Quotient of spectra in Fig 12 Flatness of curve
  again implies that the
• sinusoidal power level in spectrum is a gain
  of the feed effect.

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Comparison of Passbands measured with Matched
Loads Green and Red
with one 5 second integration on Sky
Blue and White
5
Total Power vs. Time Avg of entire band
Black Median filtered band Red
6
Total Power vs. Time Step _at_ 100 sec/step
alternate approach based on avg of
frequency channels 32803350 from band of 8192
channels
7
Dynamic Spectra first 50 min (time increases
upward)
72 MHz
74 MHz
76 MHz
74 MHz
8
Dynamic Spectra 50 min (1700-1750UT - time
increasing upward)
72 MHz
74 MHz
76 MHz
74 MHz
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Dynamic Spectra entire dataset (1120-2300 UT
- time increasing upward) passband
determined from average of median-filtered
spectra from 1123-2000 UT plots show 1 in
20 spectra all dynamic spectra are
Polarization 1
72 MHz
74 MHz
76 MHz
74 MHz
10
Time 1206 UT
11
Time 1725 UT
5120
3584
3072
2560
12
Powered UP
Powered DOWN
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Powered UP telescope movement (2003-01-09)
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Powered Down NO telescope movement (2003-01-29)
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Comparison of Galactic Pole with low
Galactic Latitude
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Difference between Galactic Pole and
low Galactic Latitude
17
Quotient low Galactic Latitude divided by
Galactic Pole