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 originally built to be used with the 47 Mhz  when studying meteors.



calibration measurements


Calibration measurements:

03jun14: on,off the crab nebula, gain, beamwidth.
20jan06: On, off 3C348.0 (Hercules A) Tsys,gain,Beamwidth,sefd


20jan06: A first look at the 47 Mhz bandpass, dynamic spectra, rfi.

03jun14: on/off the crab nebula

    On 03jun14 the crab nebula was tracked with the 47mhz receiver.
The setup was:
  Processing the data
The plots show the total power vs time and offsets (.ps) (.pdf)


processing: x101/140603/bmwid47mhz.pro

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 the 47 Mhz receiver. A 1 Mhz band centered at 46.8 Mhz was base band sampled in both polarizations.
    The sequence for data taking was: The data processing was:     The plots show the total power as we moved across the source (.ps) (.pdf) :     The first move to the peak is about 25% larger than the following two passes over the center. I'm not sure why this happened. The data should be retaken with cross scans on a source that transits closer to 18 degrees dec.

    The table summarizes the results:
cal value  polA polB Notes
calValues used (K) 5700 4792 from electronics. These are old values.
Tsys (K) 6990 6486 The Tsys from the src fit is higher. This may be a sidelobe problem.
beam width (deg) 2.1 2.1 Scaling from 430 linefeed gives a beam width of 1.5 degrees.  The 47 dipoles are under illuminating the dish by 25% (the are probably also off a little). 
Tsys/Tsrc 2.5 2.8 Using Tsys from the src fit
Flux src (3C348.0) (Jy) 1332 1332 Kuehr et al A&A suppl. vol 45, sep 81, 367-430.
SEFD (Jy) 3330 3729 this does not depend on the cal value.
Gain (K/Jy) 2.1 1.7

Notes for future cross scans:

processing: x101/060120/tpinp.pro, proc.pro

20jan06: A first look at the 47 Mhz bandpass,dynamic spectra, rfi.

    On 20jan06 20 seconds of base band data was taken with the 47 Mhz receiver.  A 1 Mhz band centered at 46.8 Mhz was recorded in both polarizations. The telescope was sitting at az=185, za=8.834 degrees while the sky drifted by (in 20 seconds the sky drifted by 4% of a beam) .A birdie at 46.92 Mhz was transmitted with the birdie maker while this data was taken. The results are:

Average spectra and rms noise (.ps) (.pdf):

Dynamic spectra of the 20 second PolA (.gif).
Dynamic spectra of the 20 second PolB (.gif).
    Dynamic spectra were computed for the 20 seconds using .2 second averaged spectra. A robust fit of a 7th order polynomial was fit to the median band passes and then used to remove the bandpass shape of each spectra. The spectral channels between 46.61 and 46.67 were averaged and then used to flatten the image. The images was then  averaged to 2048 channels. You can see :
A high resolution (1 Hz) look at some of the birdies (.ps) (.pdf):
    The spectra were recomputed with a 1 hz resolution. 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 is supposed to be by 153 Hz. This offset was also seen on the spectrum analyzer in the control room. I tested the synthesizer used to send the frequency to the birdie maker and it is locked to the station clock. It looks like the synthesizer for the 47 Mhz is either unlocked or someone dialed in the wrong frequency.
  • 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 the center.
  • Fig 1 bottom: The 5.3 second birdie at 46.689 Mhz. This has been averaged to 31 Hz. It is about 8. Khz wide. You can see that it is wandering about in frequency by a few Khz during the 5 seconds.
  • Summary:
    processing: x101/060120/dospec.pro