The standard heiles calibration scans do 4 strips across a source while the data is sampled with the correlator at a 1 hz rate. The spectra are normalized by the off source spectra and then converted to kelvins using the cal. Fits are then done to the stokes parameters (I,Q,U, and V).
Project T2212 wants to know the gain as a function of frequency (and probably angle from beam center) over a 20 Mhz bandwidth to compute the back scatter gain. The normal calibration scan processing fits 2d gaussians to the the total power (25 Mhz). This was modified to include fits by individual frequency channels.
30jan05 (.ps) (.pdf) : This data was taken after the cavity filters were installed in front of the dewar to get rid of the tv station harmonics. There were 11 patterns on B0134+329 and 18 patterns on B0340+048.
15jul06 (.ps) (.pdf) : This data was taken before the new turnstile was installed. There were 19 patterns on B0134+329 and 14 patterns on B0340+048. The data looks pretty much the same as the jan05 data.
- The total power (25 Mhz) strip data. The top plot has the 11 patterns of B0134+329 overplayed. The bottom plot has the 19 patterns of B0340+048. The dashed blue lines are the start of each of the 4 strips (60 points per strip). You can see the main beam and the sidelobes. The data is still in correlator units (Tsys is about 1.)
- BandPass and az/za coverage: The top is a typical spectral bandpass. The spectral density falloff at lower frequenceis is being caused by the 20 Mhz rf filter. The dashed red lines are the channels that were actually fit. The channels outside these lines were given the values at the dashed lines. The bump at 426 Mhz is interference. The bottom plot is the az, za position for each pattern done.
- Gain: The gain in Kelvins/Jy. The top plot is B0134+329 and the center plot is B0340+048. The gain vs frequency is plotted for each pattern. The green mask is the region that was fit. The spikes are caused by rfi. The bottom plot is the gain fit to the 25 Mhz bandwidth vs zenith angle. The gain offsets in the first two plots are being caused by the za dependence of the gain.
- Tsys: Tsys in Kelvins. The top two plots are versus frequency. The bottom plot is the 25 MHz bandwidth fit vs za. The offsets in Tsys are caused by the za dependence. B0134+329 has a Tsys that is larger than B0340+048. This is probably leakage from the source getting into the baseline. The difference is about 3 kelvins. The Temperature difference of the two sources is about 300 Kelvins so the leakage may be about 1%.
- BeamWidth: The average beam width ((az+za)/2). The offsets are being caused by the za dependence (spill over).
- Normalized gain, Beamwidth, and Tsys: The za dependent offsets were removed by normalizing each pattern to its median value (over the channels used).
- Normalized Gain:
- The normalized gains for the different patterns are repeatable. The fgain for the two sources (whose strengths differ by about a factor of 5) are also the same.
- The gain peaks around 427 Mhz and drops by about 10% as we get out to 440 Mhz. This seems like a lot. It could be that the illuminated area (probably on the tertiary) is changing with frequency.
- The ripples at about 1 Mhz spacing are real. They are the standing waves caused by the source power bouncing between the dish and the feed. They remain constant in phase as we track across the dish and between sources. For the phase to move, the reflection distance would have to change by a fraction of 70/2=35 cm. This is telling us that the reflections are coming from the dome/za rails (which remain at a fixed distance from the dish as we track in az,za) and not from the fixed platform (whose distance from the dish changes as we move in az,za)
- Normalized beam width: The beam width is falling off with the expected 1/freq dependence (the green line). It starts to deviate from this around 436 Mhz.
- Normalized Tsys: Tsys is pretty flat so the normalization by the off spectrum is working pretty good.
22jul06 (.ps) (.pdf) : This data was taken after the new turnstile was installed. It had not yet had its final tuning. There were 19 patterns on B0134+329 and 17 patterns on B0340+048. The data also looks the same as the previous data.
Comparing jan05,jul06 (.ps) (.pdf):
- Top: Gain vs frequency. Black is jan05. Blue is 15jul06 (old turnstile). Red is 22jul06 (new turnstile).
- 2nd plot: Average gain vs frequency for jan05 and jul06. The median value was taken at each frequency channel. The two jul06 datasets before and after the turnstile installation are the same. The gain above 435 Mhz was a few percent higher back in jan05 than it is now in jul06.
- 3rd plot: Beamwidth vs Frequency. The green line is 1/freq.
- Bottom plot: Average beamwidth vs frequency. The median value was taken at each frequency channel. This has remained constant for the 3 data sets.