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[linrad] Re: MAP65 and Linrad Network

Hi Leif,
One of the nuisances of using the original data file is that Linrad's raw data are not time-stamped. 

Oooh! But they are:-) Your file is stamped 1163231107.413487 which
was the output of the routine current_time() at the start of
the recording.


FB!  This is good to know.


I do not know how to interpret the MAP65 screen. The polarisation
data of AA1YN seems odd to me. They change very rapidly:
0746:  90
0748: 135
0750: 135
0752: 135
0754:   0
0756:  45


The MAP65 screen shot on my web page
http://physics.princeton.edu/pulsar/K1JT/MAP65_1.JPG is from a very early version of the program. Polarization information shown for AA1YN in the main text window is incorrect, but you can find the correct data in the window at lower right. In that panel the columns of numbers are frequency in kHz (above 144.000 MHz), additional frequency increment "DF" in Hz, polarization angle in degrees, and UTC. For AA1YN, therefore, the measured polarization angles over this block of time were 

  UTC  Pol
-----------
 0746:  73
 0748:  65
 0750:  70
 0752:  68
 0754:  66
 0756:  71
 0758:  60
In normal operation with a fully working MAP65, the main text window is used for the current QSO. New text appears there at about t=55 seconds in the receive interval. Decoding of the remainder of the bandpass takes place subsequently, and on my development computer finishes at about t=12 s into the next minute. 


Which signal on the screen that has this behaviour is not obvious to me.
The processing screen says Freq 128 and DF=0 (or very close.)
When I look at the file, I find the weak signal at the center of the lower waterfall to start at 144.129823 and drift down to 144.129814.
JT65 users conventionally use a "quasi-channelized" approach for specifying frequencies. The frequencies correspond to that of the suppressed carrier of the generated SSB signal. Calibrations on the MAp65 screen follow these conventions.
MAP65 reports the "channel frequency" as 144.128, as shown by the "128" at the beginning of the lines in the main text window and also in the panel at lower right. Owing to a combination of Doppler shift and calibration errors, the actual received frequency was higher by about +222 Hz at 0746 UTC, drifting slowly downward to +216 Hz at 0758.
The JT65 sync tone is at 1270.5 Hz. MAP65 has also subtracted 330 Hz to correct for an apparent fixed calibration error (at 144.125) in my WSE converters.
Therefore, with normal Linrad calibration you should expect to see the AA1YN signal at the frequency 

  144.1280000
   +0.0002220
   +0.0012705
   +0.0003300
 ------------
  144.1298225 at 0746 UTC.

You measured 144.129823 MHz, so we are in almost perfect agreement.


That is a 1.818 Hz frequency shift as compared to the MAP65 screen???


In this case the shift is 1270.5 + 330 + DF = 1822.5 Hz at 0746 UTC.
There is some info "Options" in the upper waterfall, but that does not fit.
In that early version of MAP65, the information there is meaningless.
The signal at 144.12982 is right hand circular in Linrad and it does not change polarisation during the 10 minutes.
I don't pay attention to the V (circular) Stokes parameter in MAP65. However, there seems to be plenty of linear polarization in the AA1YN signal, certainly enough to establish its angle pretty well. The linear polarization (major axis of the ellipse) is at about 70 degrees, perhaps rotating slightly downward over the 12 minutes. 


The strong signal at -880 Hz in the lower waterfall is at 144.12894
in Linrad. This signal is elliptic, about 50% left hand. Polarisation
does not change with time on this signal either.
This big signal is KB8RQ. MAP65 reports the linear polarization angle to be around 90 degrees, increasing somewhat during the 12 minutes.
Don't hold me too much to these polarization-angle numbers. They came from a very early MAP65 version; I was still playing with the algorithms then, and I don't recall exactly at what stage the screen-dump was made. 

	-- Joe, K1JT

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