47 receiver calibration.
The 47 Mhz receiver uses a set of dipoles that
are mounted around the carriage 430 Mhz line feed. The system was
built to be used with the 47 Mhz when studying meteors.
The First LO is a fixed synthesizer upstairs which is normally
set to 76.8
Mhz (46.8 + 30). When using the system you need to make sure
that the synthesizer
is on and set to the correct frequency (verify this with the
The IF comes out at 30 Mhz in the receiver room on the rightmost
the 30 Mhz racks. You need to switch the IF selector to 47A, 47B
If you cable up left to left, left to top, base band mix, and
into the Ri you will get the real signal in
the Q digitizer
(rightmost of pair), imaginary in I (leftmost). If you use
with the complex option and then compute the spectrum, the
be flipped. When looking at 30 Mhz on the spectrum analyzer the
20jan06: Receiver is off frequency by about 150 hz. About
that the 5 Mhz reference was not working. It has now been fixed
03jun14: on,off the crab nebula, gain, beamwidth.
20jan06: On, off 3C348.0 (Hercules A)
20jan06: A first look at the 47 Mhz
dynamic spectra, rfi.
03jun14: on/off the crab nebula
On 03jun14 the crab nebula was tracked with the
The setup was:
Processing the data
- Use the line feed model for tracking
- track the source, then move off by about 2 degrees, then move
back on source.
- Use 1 Mhz bandwidth about 46.8 Mhz
- sample the voltages with the radar Interface at 1 Mhz, i,q 8
The plots show the total
power vs time and offsets (.ps) (.pdf)
- input the voltages, compute power and then median filter
blocks of 1e6 .. this gave 1 second resolution.
- page 1: source deflection vs time
- top: offset (in degrees) from crab nebula vs time. The
dashed green line shows when we were on source.
- middle: total power vs time.
- red is pola, black is polB
- The total power was computed for each 1 usec sampled and
then median filters to 1 second resolution.
- You can see that polA (red) was wandering around
- Bottom: polB Temperature vs time
- With chris salters help we got:
- flux crab (The absolute spectrum of cas A. barrs,genzel,
- 26.3 Mhz, 2990 Jy
- 81.5 Mhz 1880 Jy
- 46.8 Mhz 2360 Jy (using the spectral index from the
- Tsys off crab: 9000K (408 Mhz survey et al +
salter, and spectral index of 2.4?)
- The gain was then 2.6 K/ Jy
- I didn't bother with polA
- Page 2: source deflection vs offset
- The source deflection vs position offset is plotted
- the horizontal dashed green line is at 1/2 the average
- the fwhm (dashed red lines) varied from .97 to 1.4 Degrees
- Pol A looks like it has some stability problems
- I've assumed that the receiver temperature is 0.
- PolB gain : 2.6 K/Jy
- fwhm beamwidth 1 to 1.4 degrees
- The baseline is difficult to measure since the crab sits in
the galaxy anti center.
20jan06: On, off 3C348.0
(Hercules A) Tsys,gain,Beamwidth,sefd2: (top)
On 20jan06 the telescope moved on and off 3C348.0 (Hercules
A B1950: ra/dec 16:48:40.4/05:03:48) while taking data with
Mhz receiver. A 1 Mhz band centered at 46.8 Mhz was base band
The sequence for data taking was:
The data processing was:
Source rising, move off source by -2 degrees in za.
Tracking 2 degrees
off, fire the cal for 14 seconds.
Move on source and sit for awhile
From -2 deg za offset drive to +4 deg za Offset (passing through
at slew rate (.04 deg/sec).
Move from +4 deg za offset to -4 deg za offset passing through
at slew rate.
Fire the cal while off source.
The plots show the total
as we moved across the source (.ps) (.pdf)
input the data, compute power and median filter to 16
Interpolate the telescope 1 second az, za positions to the
of each 16 millisecond sample.
Compute the az, za positions for the source at the time
each data sample.
Compute the Telescope Za - srcZa for each data sample. This is
offset since we only offset in the za direction.
For plotting purpose median filter the total power to .5
Compute scale factor of power counts to Kelvins using the two
the start end end of the run). The scale factors agreed to
1% (taken at the beginning and end of run).
Fit a gaussian to the power versus zenith angle offset to get
and beam width.
The first move to the peak is about 25% larger
the following two passes over the center. I'm not sure why this
The data should be retaken with cross scans on a source that
to 18 degrees dec.
Fig 1 top,middle: The total power vs time for the 700
data (top is polA, middle is polB). The green dashed line
system temperature. The red dotted lines are where we crossed
The jumps in power at the start and end are the cal being fired.
in power at 400 seconds is when we started to spill over and see
(which is much colder than the sky).
Fig 1 bottom: The zenith angle position of the
telescope. The green
* were on source.
Fig 2: Plots the power versus za offset for the data
bottom polB). The bumps at +/- 2.5 degrees are the first
dip at +4 degrees is the Tsys going down because of the spill
>> Tground). The green line is the gaussian fit. The
sidelobes and above
+ 2 deg were not used in the fit.
The table summarizes the results:
|calValues used (K)
||from electronics. These are old values.
||The Tsys from the src fit is higher. This may be a
|beam width (deg)
||Scaling from 430 linefeed gives a beam width of 1.5
The 47 dipoles are under illuminating the dish by 25% (the
also off a little).
||Using Tsys from the src fit
|Flux src (3C348.0) (Jy)
||Kuehr et al A&A suppl. vol 45, sep 81, 367-430.
||this does not depend on the cal value.
Notes for future cross scans:
processing: x101/060120/tpinp.pro, proc.pro
When redoing with cross scans try not to spill over so the
To move 4 degrees in za takes about 1.6 minutes at slew rate.
probably want to go a little slower so the telescope can catch
The pointing model is that of the line feed. Looks like it might
be a bit
off. The cross scan should tell us that.
20jan06: A first look at
the 47 Mhz bandpass,dynamic spectra, rfi.
On 20jan06 20 seconds of base band data was taken
the 47 Mhz receiver. A 1 Mhz band centered at 46.8 Mhz was
in both polarizations. The telescope was sitting at az=185, za=8.834
while the sky drifted by (in 20 seconds the sky drifted by 4% of a
.A birdie at 46.92 Mhz was transmitted with the birdie maker while
data was taken. The results are:
and rms noise (.ps) (.pdf):
of the 20 second PolA (.gif).
Fig 1 top: Spectra of 4096 channels (244 hz resolution)
and then averaged to .2 seconds. This gave 95 spectra for the 20
The median bandpass was computed, normalized to the median
and then plotted. The birdie at 46.8 Mhz is the Dc offset of the
The birdie at 46.92 Mhz comes from the birdies maker.
Fig 1 middle: This is a blowup of the median bandpass.
half of the band is a lot rattier than the higher frequency
Fig 1 bottom: The total power versus time is plotted.
peaks every 5.3 seconds.
Fig 2: The rms/Mean was computed fore each channel of
the 95 spectra
and plotted. The bottom plot is a blowup. The expected value is
by the radiometer equation. In this case the value should be
bottom plot shows that the noise statistics are what we expect
small rise as we move toward the edge of the band (probably
the filters). The largest variability is at 46.689 Mhz.
of the 20 second PolB (.gif).
Dynamic spectra were computed for the
seconds using .2 second averaged spectra. A robust fit of a 7th
was fit to the median band passes and then used to remove the
shape of each spectra. The spectral channels between 46.61 and
averaged and then used to flatten the image. The images was
averaged to 2048 channels. You can see :
high resolution (1 Hz) look at some of the birdies (.ps) (.pdf):
5.3 second rfi at 46.689 Mhz
the birdie maker birdie at 46.92
A birdie at 47 Mhz with side bands
A birdie at 46.66 that wanders around.
The spectra were recomputed with a 1 hz
This gave 20 spectra over the 20 seconds.
Fig 1 Top: This is blowup of the 46.92 Mhz birdie
generated by the
birdie maker (15.64*3 Mhz). The birdie is offset from where it
to be by 153 Hz. This offset was also seen on the spectrum
the control room. I tested the synthesizer used to send the
the birdie maker and it is locked to the station clock. It looks
synthesizer for the 47 Mhz is either unlocked or someone dialed
Fig 1 center: A blowup of the birdie at 47.000452 Mhz.
It was not
resolved in the 1 hz channels. The sidelobes are 11.403 Khz from
Fig 1 bottom: The 5.3 second birdie at 46.689 Mhz. This
averaged to 31 Hz. It is about 8. Khz wide. You can see that it
about in frequency by a few Khz during the 5 seconds.
The noise statistics for the receiver are correct.
The receiver's 1st lo is probably unlocked. (note 01feb06.. 5
was not working. It has now been fixed).
There is a birdie with a 5.3 second period near 46.689 Mhz. It
is 8 khz
wide and wanders by a few Khz every period.
There is a narrow birdie (< 1 hz) a 47.00452 Mhz with side
11.403 Khz from the center.
The low frequency half of the band is a lot noisier than the