Lbn cal values measured 28jan02
The cal values for lband narrow were measured
on 28jan02 in the early morning using the sky/absorber
technique. The only difference was that the telescope was not tracking
blank sky. The cal on/off times were 10 seconds (drift time for about 1
beam) so the on /offs were contaminated by sources drifting
through the beam. This data was taken with the radar blanker on for both
the sky and absorber (the absorber data looks better than the dec01 absorber
data without the blanker on).
The cals were computed separately by myself and
karen O'neil. The values computed by karen were installed 11jul02
retroactively to 01sep01.
Phil's computation of the
and karen's cal values.
The temperatures used in the computation were:
of the cals:
Each frequency band was measured 9 separate times on the absorber and
21 separate times on the sky. For each measurement the calon/off-1 spectrum
was computed and then the 9 or 21 separate measurements were cumfiltered
to remove rfi. The calValue
versus frequency plots show the results.
of calOn/Caloff-1 for the 21 sky measurements also shows the jumps
do to the sources. Each colored line should be continuous. The vertical
jumps at 100 Mhz boundaries are the sources in the on or the off. You can
also see the rfi (before filtering) in the 1200 to 1300 Mhz band and the
1500 to 1600 Mhz band. The plot is calon/caloff-1 so the rfi can be in
the on, or the off, or both.
Fig 1 is the cal value in deg K versus frequency. The * are the measurements
and the lines are the cumfiltered values at each frequency. The colors
are: Blue is measured using the sky and absorber ratio. Black is using
just the absorber and red is using just the sky. The Top plot is polA and
the bottom plot is polB. The purple line is the current cal value (with
the 6% error). The light blue line is the current cal value after correcting
for the 6% error. The cal value from the sky does not agree very well with
the values from the absorber and absorber, sky ratio.
Fig 2 and 3 show the cal values for each measurement (polA, polB). The
top plot has the 9 measurements on the absorber. The center plot shows
the 21 measurements on the sky. The bottom plot is the absorber, sky ratio.
The center there has jumps in the 1300 to 1400 range. These are source
drifting through the beam (4*25Mhz=100 Mhz is measured at each step).
The final plot
has the power levels during the measurements.
Fig 1 top is the power at the upstairs fiber optic transmitter for all
of the measurements. Each green vertical line delimits a single pass through
1200 to 1600 Mhz (there were 9+21=30 in total). This averages over 500
Mhz and is taken before the start of each 100 Mhz band.
Fig 1 center is the power at the downstairs if power meter.
Fig 2 plots the 50 Mhz band (via the power counters) that is input to the
correlator 8 bit a/d converter. Top to bottom is correlator board 1 (first
25 MHz of 100 MHz section) through board 4 (last 25 MHz of the 100 Mhz
section). The level has been divided by the median value (the scale is
linear in power). Up to sample 600 it is relatively clean (we are on the
absorber). After this we move to sky and you can see the radar's pop up.
Fig 3 plots the 25 Mhz 9 level total power measured via the 0 lag of the
correlator. A 25 MHz digital filter sits between the power counter of figure
2 and this measurement. The rfi does not look as bad. Unfortunately some
of the spikes at the 50 MHz stage that are outside the 25 MHz band have
probably saturated the a/d converter so the 25 MHz values may be corrupted
were there is large rfi in the 50 MHz band.
Karen O'neil separately computed the cal values from
the 28jan02 using different rfi excision techniques. The first figure
compares the old cals, karen's cals, and phil's cals:
phil's and karen's cal values: (top)
The second set of plots compares
the gain and Tsys of lbw to lbn using karen's and phil's cal values.
All of the calibration scans for lbw and lbn between sep01 and may02 were
used. The common frequencies for the two receivers were used: 1300, 1375,
and 1415 Mhz. The sources for the two receivers were different so any flux
density error do not cancel.
fig top: The cal values in kelvins. black:karen, red:phil, green: old cal
values (after correcting for 6%error).
fig middle: ratio of "new" cal to old cal. black:karen's computations,
fig bottom: Ratio of phil's cal values/ karen's cal values.
Karen's cal values were installed as the current cal values on 11jul02.
They will be used for data taken after 01sep01 (to match the new gain curves).
Fig 1. Gain versus za. black:lbw gain, green:lbn gain using phil's cals,
red: lbn gain using karen's cals. The lbn gain is lower than that of lbw.
At 1300 and 1375 Mhz phil's values lie closer to lbw than karen's.
at 1415 both karen's and phil's cal values give the same gain.
Fig 2. Tsys for lbw and lbn using karen's and phil's cals. A third order
polynomial is also fit to the data.
Fig 3. The SEFD (system equivalent flux density) for lbn and lbw. This
is Jy per Tsys and is independent of the cal values.
Fig 4. If the gains of the lbw and lbn are the same, then the ratio of
the LBWsefd/LBNsefd should be determined by the ratio of the system temperatures
(which are determined by the cals). This plot compares the SEFD ratio to
the Tsys ratio. Black:SEFDLBW/SEFDLBN, red:TsysLbw/TsysLbn using karen's
cals. green: TsysLbw/TsysLbn using phil's cal values. The Tsys measurements
do not match the sefd ratios. They differ by up to 13 %. For 1300 and 1375
Mhz,Phil's cal values are closer to the sefd ratio than karen's.