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This program is used to analyse pulsars of known parameters. It contains
both a post-detector spectral display, and a "pulse profile" display.
It has a built-in de-dispersion filter that will work up to DM=100 for
21cm observing, and up to DM=5 for 327Mhz observing.
The program takes the following options:
--rx-subdev-spec which USRP Rx side? A or B
--decim USRP decimation rate use either 64 or 128
--freq USRP daughtercard frequency
--observing Actual observing frequency (default is to use the
setting for --freq)
--avg Averaging setting for spectral display--higher numbers
equal more averaging. 25 to 40 is typical.
--favg Pulse folding averaging. 2 to 5 is typical.
--gain USRP daughtercard gain control
--reflevel Reference level on pulse profile display
--lowest Lowest spectral bin that is considered valid, in Hz
--longitude Observer longitude: West is negative
--latitude Observer latitude: South is negative
--fft_size Size of FFT for post-detector spectrum: default is 1024
--threshold Threshold (dB) to be considered a spectral "peak"
This is relative to the average spectral level
--lowpass Low pass frequency for post-detector spectral display
20-100 is typical
--prefix Filename prefix to use for recording files
Default is ./
--pulsefreq The frequency of the expected pulses
For sentimental reasons, this defaults to 0.748Hz
--dm The DM
--doppler The doppler shift, as a ratio
--divbase The base of the Y/Div menu in pulsar display
--division The initial Y/Div in pulsar display
DM, Doppler, Gain, Frequency, and the averaging parameters can all be
changed using the GUI at runtime.
If latitude and longitude are set correctly, and the system time is
correct, then the current LMST is displayed below the frequency
input, updated once per second.
Moving the mouse in the post-detector spectrum display shows you that
point in the post-detector spectrum, both frequency and signal level.
The post-detector spectrum is analysed, with results shown below
"Best freq". It shows the spectral peaks, and computes their relationship.
It shows the harmonic compliance among the peaks, as well as the average
peak-to-peak distance.
Here's a complete example for observing a pulsar with a frequency of
1.35Hz, at 431.5Mhz, using an IF of 10.7Mhz, and a DM of 12.431, using
1Mhz observing bandwidth:
./usrp_psr_receiver.py --freq 10.7e6 --decim 64 --dm 12.431 --avg 35 \
--pulsefreq 1.35 --fft_size 2048 --lowest 1.00 --gain 75 --threshold 11.5 \
--observing 431.5e6 --reflevel 200 --division 100 --divbase 10 --favg 3 \
--lowpass 20 --longitude -76.02 --latitude 44.95
Since the observed pulsar is at 1.35Hz, a lowpass cutoff for the
post-detector spectral display of 20Hz will be adequate. We
tell the spectral analyser to use a threshold of 11.5dB above
average when analysing spectral data, and set the epoch folder
averager (pulse profile display) to use an average from 3 samples.
Notice that our actual USRP/Daughtercard frequency is 10.7Mhz, while
our observing frequency is 431.5Mhz--this is important in order for
the DM de-dispersion calculations to be correct. We also set our
latitude and longitude, so that logfiles and the LMST display
will have the correct LMST in them.
The entire complex baseband can be recorded, if the "Recording baseband"
button is pressed. Filenames are generated dynamically, and a header
file is produced giving observation parameters. The baseband data are
recorded as octet pairs: one for I and one for Q. Pressing the button again
turns off baseband recording. This baseband is "raw", so it will
not have been de-dispersed. The data rate will be whatever the
USRP was programmed to at the time (based on --decim).
The files are: YYYYMMDDHHMM.pdat and YYYYMMDDHHMM.phdr
The .phdr file contains ASCII header information describing the
contents of the .pdat file.
Similarly the raw, pre-folded, band-limited post-detector "audio" data can be
recorded using the "Record Pulses" button. The data rate for these is
currently 20Khz, recorded as short integers. Just like baseband recording,
pressing the button again turns off pulse recording.
The files are: YYYYMMDDHHMM.padat and YYMMDDHHMM.pahdr
The .pahdr file is ascii text providing information about the contents
of the corresponding .padat file.
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