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[Linrad] MAP65 for SDR-IQ
- Subject: [Linrad] MAP65 for SDR-IQ
- From: Joe Taylor <Princeton.EDU; joe@xxxxxxxxxxxxxxxx>
- Date: Fri, 13 Feb 2009 15:08:45 -0500
Many people have asked about a version of MAP65 that could
be used with the SDR-IQ receiver. I'm happy to report that
an operational version of "MAP65-IQ" now exists. It should
be ready soon for testing by others.
You'll recall that MAP65 works together with Linrad in a
dual polarization or "stereo receive" system. It takes
advantage of many of Linrad's excellent features -- the
waterfall displays, noise blanker, dual-channel coherent
processing, etc. -- as its receiving "front end". Partially
processed data are sent from Linrad to MAP65, which searches
for all JT65B signals in a 90 kHz bandwidth, measures the
polarization angle of each one, and decodes them all. The
Linrad sample rate must be set to 96000 Hz.
MAP65-IQ differs from the standard MAP65 in respects:
1. MAP65-IQ is intended for use with single-polarization
systems. (Thus, no polarization matching can be done.)
2. MAP65-IQ uses a slightly different sample rate, 95238.1
Hz, in order to be compatible with the SDR-IQ hardware.
MAP65-IQ appears to work very well. In one test using the
H-polarization (horizontal) data from 11 minutes of the 2006
ARRL EME Contest, MAP65-IQ decodes 82 messages from 24
different stations spread over the range 144.100 - 144.160
MHz. For comparison, the standard MAP65 decodes 127
messages from 36 stations in the same 11 minutes of data,
using both H and V polarizations. For a rough sensitivity
calibration, I was using a pair of 2MXP20 yagis when these
data were recorded.
These results are just what one would expect: the somewhat
smaller number of messages decoded by MAP65-IQ is a result
of its having no access to data in the "other" polarization.
In order to make tests of MAP65-IQ you'll need a receiving
setup with Linrad and an SDR-IQ, and you must be familiar
with the use of JT65 in WSJT. If you meet these
requirements and would like to participate in early tests of
MAP65-IQ, please send me an email with some details.
-- 73, Joe, K1JT
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