[Linrad] Notes on Linrad/MAP65-IQ/SDR-IQ

[N6KK <gmail.com; jrb17521@xxxxxxxxxxxxxxxx>]

Notes on Linrad/MAP65-IQ/SDR-IQ:

Equipment:

2x5MWL, preamp, XV144, K3, 1.5KW amp, SDR-IQ
2.8 GHz P4, 1.5 GB RAM, D44 soundcard
XP Pro (SP 3), MAP65-IQ, Linrad (3.02)

Issues and solutions:

1)  I use the IF output (8.21 MHz) from the K3 to feed the SDR-IQ.
The passband at that point is inverted, so I had to rediscover (since
I've been down this path before) the parameters in Linrad that needed
to be changed and recompile.  No big deal.
2)  The (much reported) loop-back address in the par_netsend_ip file
requires a carriage return after the ip address. Otherwise it appends
*.100, so you end up with a bad ip.
3)  Setting Linrad's priority to High resulted in Linrad freezing
immediately.  So far priority of Normal seems to be working OK.
4)  Linrad would run for a few minutes, then freeze.  Just before each
freeze, there was a spike in CPU utilization (from ~30% to 100%).  In
addition, after a click in the wide waterfall to select a signal of
interest, any click on the high resolution spectrum or baseband
spectrum would intermittently cause a black screen with an
unrecognized error code (which I didn't write down, duh!) and request
to quit the program.  After investigating, it seems something in the
Zone Labs firewall wasn't happy.  After removing the firewall and a
reboot Linrad has run with no problem for 12 hours so far.

5)  Another potential issue was that I had the power saving feature
configured to turn the hard drives off after 4 hours.  Normally that’s
not a problem as everything runs out of RAM, but if a program
(Linrad?) requires a quick disk access and the drives have been
powered down and take a few seconds to spin up, the resulting delay
could cause a problem.  The hard drives are now powered all the time.

6)  For the K3 IF of 8.215 MHz and a center frequency of 144130, I
needed to change the MAP65-IQ parameter Fadd to (144130-8215) 135915
based on some of Joe's comments and the code (which I took a peak
at).  For an 80 KHz display range, I changed Fmin to 90 and Fmax to
170 (130 +/- 40), and the top of the MAP65-IQ waterfall displays 215
+/- 40, as expected.  Moving the cursor in the waterfall shows (after
adjusting Fadd a bit) the last three digits of the received frequency
at the top of the display.  That number is also reported as the
frequency in the decoded outputs.  Cool …

7)  My noise environment is very bad and I'd like to get the Linrad
smart noise blanker running, but it needs a calibration file for this
particular sample frequency.  Since the SDRs don't require individual
calibration like the WSE units do, can you make one up and put it on
your website Leif?

8)  The MAP65-IQ displayed time for decodes is the local computer
time, not UTC, although the moon az and el computations are correct
and the time in the lower left block is in UTC.

9)  The power out from the XV144 goes from about 7 watts for the
lowest MAP65 tone to 3 watts for the highest tone.  I think this has
something to do with the K3 setup, but I'm working on it.

I still have lots of tweaking to do, but yesterday and today I copied
numerous stations across the band (even with extremely high noise).
The narrow band decoder does seem to be more sensitive than the
wideband, but that's just a first impression.  This is definitely a
large step forward for EME with the SDR-IQ!

Thanks Joe and Leif for making this happen!

Joe N6KK



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