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[Linrad] Re: Linrad and MAP65-IQ
- Subject: [Linrad] Re: Linrad and MAP65-IQ
- From: Joe Taylor <Princeton.EDU; joe@xxxxxxxxxxxxxxxx>
- Date: Mon, 09 Mar 2009 12:00:04 -0400
Hello Moonbouncers,
Back home again and with some free time on Sunday evening, I
fired up the EME station at K1JT and made some
side-by-side tests of MAP65 and MAP65-IQ on 2 meters. This
note is a brief summary of the results.
My antenna on 2m is a 4x14 xpol array with separate
tower-mounted preamps for each polarization and separate Rx
feedlines. In the shack the two signals go to a
WSE-converter chain and then to a Delta44 sound card on
"Computer A", running xlinrad under Linux. MAP65 runs under
Windows XP on Computer B, and the two computers share an
ethernet connection.
For these tests I tapped off the V-pol signal at 10.7 MHz
from the WSE-converter chain and used this as input to the
SDR-IQ. Computer B ran Linrad (version 3.02) and MAP65-IQ
(r1089) as well as MAP65. (Computer B is a 2.8 GHz
dual-core machine with 2 GB memory, and it had no difficulty
running Linrad, Map65, and MAP65-IQ simultaneously.) Linrad
was set to "Above Normal" priority. The Windows Task
Manager showed CPU usage <10% except near the end of each Rx
minute, when usage rose for a few seconds to 100% as the two
MAP65 programs did their decoding. Linrad continued running
smoothly during these times, with no glitches or
discontinuities.
As others have noted, this early version of MAP65-IQ has
some rough edges. Setting it up requires extra effort to
get the frequencies right; and even when you have done this
correctly, the displayed frequency and time information has
some errors. I assure you that these problems are trivial
and temporary; they are a result of my wish to get this very
first alpha release of MAP65-IQ quickly into the hands of
some knowledgeable users, to gain some understanding of how
it would play in other stations than my own.
All in all, I found MAP65-IQ to perform very well. I made 5
or 6 EME QSOs in a couple of hours, but mostly I just
monitored the band and watched for differences between what
was being decoded by the MAP65 and by its
polarization-challenged little brother, MAP65-IQ.
You can get a fairly good impression of what I observed from
snapshots of the "Band Map" and "Messages" windows of the
two programs posted at the following links:
http://physics.princeton.edu/pulsar/K1JT/MAP65-IQ_Band_Maps.PNG
http://physics.princeton.edu/pulsar/K1JT/MAP65-IQ_Messages.PNG
In these pictures the MAP65-IQ window is on the left, MAP65
on the right. (Please ignore the 600 kHz frequency offset
and 4 hour time offset in the MAP65-IQ displays. These
errors will be fixed soon.)
If you need some help interpreting the pictures and haven't
used MAP65, you may want to read the following two documents:
http://physics.princeton.edu/pulsar/K1JT/MAP65_Status.txt
http://physics.princeton.edu/pulsar/K1JT/MAP65_Quick_Start.txt
The side-by-side comparisons show just about what one would
expect for single-polarization and dual-polarization
systems. The MAP65-IQ Band Map shows that 16 different
stations were decoded over the past few minutes when the
snapshot was made, while MAP65 decoded 25.
In the right-hand "Messages" window you can see exactly why
several of the stations were not decoded by MAP65-IQ: for
example, at 144.144 EB3DYS was received by MAP65 at
polarization angle 45 deg and SNR=-24 dB. With a V-only (90
deg) polarization capability, MAP65-IQ would then see about
SNR=-27 dB, normally too weak for decoding in a single
transmission. Similar conditions exist for K0AWU (pol=131
deg, SNR=-25 dB) and K8TL (pol=161 deg, SNR=-24 dB), and
several other stations that you would need to scroll back
the messages window to see: RZ4HF (pol=177 deg, SNR=-17
dB), YU1IO (pol=23 deg, SNR=-20 dB).
Careful examination of the two Messages windows shows that
MAP65-IQ and MAP65 usually report the same SNR for all
signals with polarization angles within +/-20 deg of 90 deg.
(Note that MAP65-IQ always reports pol=0 deg; however, in
this test it was connected to my V-pol antenna.) Signals
more than 20 deg away from vertical are weaker in the
MAP65-IQ output by the expected amounts: about 1 dB down at
+/-30 deg, 3 dB at +/- 45 deg, etc.
If you're confused by the multiple appearances of WA2FGK and
K1OR in the pictures for the same decoding minute: Herb and
John are within tropo range, so I often see their direct and
aircraft-reflected signals as well as their EME signal. The
tropo signals are mostly horizontally polarized, so the
V-pol MAP65-IQ system usually does not see them.
I had some fun when the callsign AA7A popped up on my
MAP65-IQ screen. I knew that Ned was testing MAP65-IQ at
his station ... so when he finished a QSO, I called him on
an arbitrary frequency some 30 kHz down the band. Sure
enough, he came right back on my frequency -- and we had a
nice QSO, ending with Ned saying "I CANT HIDE".
I'm traveling for QRL again near the end of this week, but
after that I hope to find time to put together another
MAP65-IQ release with known bugs corrected. I imagine that
most potential users will opt to run both Linrad and
MAP65-IQ on the same computer, under Windows, so I may try
including the latest linrad.exe in the package, along with a
full set of Linrad parameter files set up in a reasonable
way for the SDR-IQ/Linrad/MAP65-IQ combination. This could
make it much easier for first-time users to get this
somewhat complex system of hardware and software working. A
wideband, panoramic receiver that decodes every JT65 signal
it finds is well worth the effort!
As always, your feedback on Moon-Net or the Linrad reflector
will be appreciated.
-- 73, Joe, K1JT
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