[Linrad] Re: First real EME tests with MAP65-IQ

[Joe Taylor <Princeton.EDU; joe@xxxxxxxxxxxxxxxx>]

Hi Gabriel,

Many thanks, as always, for your feedback!

Gabriel - EA6VQ wrote:
> Yesterday I spent several hours playing with the new version 
> r1102, and using the default configuration of Linrad provided 
> with that version.  This is the first time I have managed to 
> decode signals using MAP65 and I must say the first impression 
> is excellent, however I have noticed several things possibly 
> not working as good as I could expect, at least with my setup:
> 
> First, the signal levels reported for the selected frequency 
> are between 3 and 5 dB weaker than with WSJT6.  I was running 
> MAP65 and WSJT6 in parallel and I could see that difference 
> for all signals. When a signal is, for instance, -22 dB in 
> WSJT6, the same signal is between -25 and -27 dB in MAP65.  
> When the band is noisy the difference is smaller (might be 
> 1 dB weaker in MAP65), possibly because of the excellent 
> noise blanker of Linrad.

The differences you describe suggest a problem somewhere in 
your configuration.  Leif has given you some suggestions 
about setting signal levels.  Here are a few more.

I am surprised by the horizontal "streakiness" of the 
example of Linrad's waterfall display that you sent me. 
That does not look right.  I note also the yellow number 
"19" in the upper left corner of the high resolution graph. 
  This means that at the time of this snapshot, 19% of your 
data were being killed by what Leif calls the "dumb" noise 
blanker.  This is not usually a good situation...

The JT65 signal showing in the baseband waterfall does not 
look right.  For that matter, the JT65 signal at about 
144.134 in the wide waterfall does not look right, either. 
One expects the sync tone to be somewhat more prominent. 
Was it being zapped by the blanker?

> Also, weaker signals (-28 to -30 dB in WSJT6) are not decoded 
> at all in MAP65 (and they are in WSJT6)

Again, this suggests that something is not right in your setup.

> Additionally, the reception of MAP65-IQ suddenly stops.  The 
> waterfall display does not update and the program doesn't 
> decode, although apparently it continues receiving data from 
> Linrad (at least it does not show "no data" or so).  When 
> I double click on the waterfall it starts receiving again.  
> This has happened at least 5 times in about 2 hours.

I have not observed similar behavior, so I cannot usefully 
comment.  Most of my on-the-air tests have been with a 2.4 
GHz dual-core machine with lots of memory, but I have also 
runs some tests with both Linrad and MAP65-IQ running in a 
1.4 GHz P4 laptop with only 512 MB memory.  I have not seen 
any  behavior such as you describe.

> Finally, near the moonset the band was really noisy and I 
> noticed that some signals that were clearly visible in 
> Linrad's waterfall were not visible at all in MAP65's 
> waterfall, and it did not decode them either.  Anyway this 
> was only in very noisy conditions, due to power lines.  
> (Joe, I have some screenshots of these last 2 situations, 
> and I will E-Mail them to you)
> 73. Gabriel - EA6VQ

You should not be seeing those horizontal streaks in your 
waterfall displays.  It's hard to know what to advise that 
you need to change; Leif's suggestions about signal levels 
and those above are a good place to start.

I did not have much time at the radio over the weekend, but 
I did run MAP65 and MAP65-IQ in parallel for half an hour or 
so.  For this test Linrad was running under Linux on an old 
computer (as usual for my xpol system).  On the 2.4 GHz 
dual-core machine I ran a second copy of Linrad, using the 
SDR-IQ for input and of course receiving only one 
polarization, as well as MAP65 (for the xpol system) and 
MAP65-IQ (for the single-pol system).

There was a big pile-up calling and working E51EME at the 
time -- congratulations on your own QSO, which I recorded -- 
and MAP65-IQ decoded many of the calling stations as well as 
E51EME.  MAP65 decoded more of the calling stations than did 
MAP65-IQ -- sometimes as many as ten in a single minute -- 
but the ones decoded by MAP65, but missed by MAP65-IQ, were 
nearly always the ones with polarization close to 90 degrees 
away from being matched to the single-pol system.  The 
signal levels reported by MAP65-IQ and MAP65 were usually 0 
or +/-1 dB for stations that were within 30 deg or so of the 
matched polarization angle.  In short, I observed no 
problems with the sensitivity of the MAP65-IQ decoder.  On 
one or two occasions, MAP65-IQ decoded a signal that MAP65 
missed.  This was an extreme situation, to be sure -- there 
were at least 10-20 JT65 signals, all blasting away within 
+/- 1 kHz of the band.

	-- 73, Joe, K1JT

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