MAP65 Status
------------
I have now established the necessary network connection
between Linrad and MAP65. So far, I have found nothing to
prevent a happy marriage!
MAP65 receives a full 90 kHz of xpol signal from Linrad,
finds all the JT65 signals in that bandwidth, matches the
linear polarization angle of each one, decodes the messages,
and provides the operator with a "band map" showing
callsigns, operating frequencies, polarization angles, and
message contents over the past 15 minutes or so. The
program provides a full-width waterfall display and another
one "zoomed in" on the frequency of the station currently
being worked.
Questions about Linrad's TIMF2 Multicast Data
---------------------------------------------
Header information accompanying Linrad's multicast TIMF2
data includes two single-byte parameters, "userx_no" and
"passband_direction", about which I have questions. I
understand that userx_no should correspond to the number of
RF channels, with negative sign indicating floating format.
I would have expected the value -4 for my system using
xpol antennas and the WSE converters (I and Q for each of
two polarizations), but in fact I see -2. Is this as it
should be?
Similarly, I would have expected passband_direction=1 as I
have no LO's on the high side and the spectrum is not
inverted. However, Linrad sends passband_direction=-1. Is
this correct?
Linrad FFT Versions
-------------------
I have been using FFT Version 0 for the first forward, first
backward, and second forward FFTs. This produces
floating-point TIMF2 data on the multicast network.
To save on memory usage in MAP65 it may be desirable to use
16-bit data for TIMF2. I have effected this by setting
first forward FFT to version 5, first backward FFT to
version 1, and second forward FFT to version 2. Are these
good choices? Is there any downside to their use that I
might not have thought about? Also, with these settings I
notice that the signal in the high resolution graph (red dB
lines) is higher than it was with FFT versions 0. Should I
adjust some other parameter to bring this level down be
several dB?
MAP65 with Windows, Linux, FreeBSD, Winrad, SDRxxx ... ?
------------------------------------------------------------
Like WSJT, MAP65 runs on both Windows and Linux. (It should
also run on FreeBSD and Macintosh, but I can't test those
here.) In my station I will probably run Linrad under Linux
and MAP65 on Windows, on a second computer.
In response to questions I have been getting: MAP65 could
run with Winrad or with various SDR's if their software is
modified to provide the necessary multicasting capability.
In itself, this would not be too difficult.
However, one of the most important MAP65 features is its
automatic Rx-polarization-matching capability. That
requires a receiver with full xpol processing, which (as far
as I know) is not now provided by Winrad, SDR-1000, SDR-14,
or SDR-IQ.
-- 73, Joe, K1JT
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