[linrad] Re: MAP65 and Linrad Network

[Leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Joe,

> I have the original raw data file and have placed it at 
> http://physics.princeton.edu/pulsar/K1JT/061111_0744.raw.bz2
Excellent:-)

> 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.
 
double current_time(void)
{
struct timeval t;
gettimeofday(&t,NULL);
return 0.000001*t.tv_usec+t.tv_sec;
}

This is the time in seconds with six decimals since Epoch
and if you run Linrad on the file with a fast waterfall
you will see the time on the waterfall starting at 07.45.08

Unfortunately I have missed to put the correct time in the 
time variable of the network packets. Currently the time
is the time when data was read from the hard disk and not
when it was stored there. I will correct for the next version:-)

The 'S' file only has a single time stamp for when write was
started. With Delta 44 soundcards, the sampling rate is 
pretty accurately 96 kHz (96014 Hz with the card in this 
particular computer.) I think one can safely assume that
the error is well below 0.05% so in a 1 hour recording
the time error at the end should stay well below 2 seconds.

> As you know, JT65 
> transmissions must start at the top of a UTC minute.  To use 
> the raw data file effectively with MAP65 you will need to do 
> something to ensure that the multicast packets contain times 
> that are close to being "correct" with respect to the 
> original time (modulo 60 seconds).
OK. I hope that you have found the time to be correct when
receiving timf2 data from Linrad in real time.

> > Surely, for MAP65 testing and development I agree that your
> > strategy is more convenient - but from my point of view the
> > original file is far more interesting....
> 
> Yes.  It probably will be far more interesting, for you 
> especially.  You will find plenty of birdies and other junk 
> in the test file!!  See 
> http://physics.princeton.edu/pulsar/K1JT/MAP65_1.JPG .
Fine!

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

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.
That is a 1.818 Hz frequency shift as compared to the MAP65 screen???
There is some info "Options" in the upper waterfall, but that does not 
fit. The signal at 144.12982 is right hand circular in Linrad and it 
does not change polarisation during the 10 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.

How do I compute the true frequency of the sync tone from the data 
in the MAP65 screen? 

73

Leif / SM5BSZ


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