1 This program is used to analyse pulsars of known parameters. It contains
2 both a post-detector spectral display, and a "pulse profile" display.
3 It has a built-in de-dispersion filter that will work up to DM=100 for
4 21cm observing, and up to DM=5 for 327Mhz observing.
6 The program takes the following options:
8 --rx-subdev-spec which USRP Rx side? A or B
10 --decim USRP decimation rate use either 64 or 128
12 --freq USRP daughtercard frequency
14 --observing Actual observing frequency (default is to use the
17 --avg Averaging setting for spectral display--higher numbers
18 equal more averaging. 25 to 40 is typical.
20 --favg Pulse folding averaging. 2 to 5 is typical.
22 --gain USRP daughtercard gain control
24 --reflevel Reference level on pulse profile display
26 --lowest Lowest spectral bin that is considered valid, in Hz
28 --longitude Observer longitude: West is negative
30 --latitude Observer latitude: South is negative
32 --fft_size Size of FFT for post-detector spectrum: default is 1024
34 --threshold Threshold (dB) to be considered a spectral "peak"
35 This is relative to the average spectral level
37 --lowpass Low pass frequency for post-detector spectral display
40 --prefix Filename prefix to use for recording files
43 --pulsefreq The frequency of the expected pulses
44 For sentimental reasons, this defaults to 0.748Hz
48 --doppler The doppler shift, as a ratio
50 --divbase The base of the Y/Div menu in pulsar display
52 --division The initial Y/Div in pulsar display
54 DM, Doppler, Gain, Frequency, and the averaging parameters can all be
55 changed using the GUI at runtime.
57 If latitude and longitude are set correctly, and the system time is
58 correct, then the current LMST is displayed below the frequency
59 input, updated once per second.
61 Moving the mouse in the post-detector spectrum display shows you that
62 point in the post-detector spectrum, both frequency and signal level.
64 The post-detector spectrum is analysed, with results shown below
65 "Best freq". It shows the spectral peaks, and computes their relationship.
66 It shows the harmonic compliance among the peaks, as well as the average
67 peak-to-peak distance.
70 Here's a complete example for observing a pulsar with a frequency of
71 1.35Hz, at 431.5Mhz, using an IF of 10.7Mhz, and a DM of 12.431, using
72 1Mhz observing bandwidth:
74 ./usrp_psr_receiver.py --freq 10.7e6 --decim 64 --dm 12.431 --avg 35 \
75 --pulsefreq 1.35 --fft_size 2048 --lowest 1.00 --gain 75 --threshold 11.5 \
76 --observing 431.5e6 --reflevel 200 --division 100 --divbase 10 --favg 3 \
77 --lowpass 20 --longitude -76.02 --latitude 44.95
79 Since the observed pulsar is at 1.35Hz, a lowpass cutoff for the
80 post-detector spectral display of 20Hz will be adequate. We
81 tell the spectral analyser to use a threshold of 11.5dB above
82 average when analysing spectral data, and set the epoch folder
83 averager (pulse profile display) to use an average from 3 samples.
84 Notice that our actual USRP/Daughtercard frequency is 10.7Mhz, while
85 our observing frequency is 431.5Mhz--this is important in order for
86 the DM de-dispersion calculations to be correct. We also set our
87 latitude and longitude, so that logfiles and the LMST display
88 will have the correct LMST in them.
90 The entire complex baseband can be recorded, if the "Recording baseband"
91 button is pressed. Filenames are generated dynamically, and a header
92 file is produced giving observation parameters. The baseband data are
93 recorded as octet pairs: one for I and one for Q. Pressing the button again
94 turns off baseband recording. This baseband is "raw", so it will
95 not have been de-dispersed. The data rate will be whatever the
96 USRP was programmed to at the time (based on --decim).
98 The files are: YYYYMMDDHHMM.pdat and YYYYMMDDHHMM.phdr
100 The .phdr file contains ASCII header information describing the
101 contents of the .pdat file.
103 Similarly the raw, pre-folded, band-limited post-detector "audio" data can be
104 recorded using the "Record Pulses" button. The data rate for these is
105 currently 20Khz, recorded as short integers. Just like baseband recording,
106 pressing the button again turns off pulse recording.
108 The files are: YYYYMMDDHHMM.padat and YYMMDDHHMM.pahdr
110 The .pahdr file is ascii text providing information about the contents
111 of the corresponding .padat file.