[Linrad] Re: MAP65-IQ Issues

[VK2KU <clearmail.com.au; vk2ku@xxxxxxxxxxxxxxxx>]

For the last few days I have been running Linrad/MAP65-IQ
in parallel with a conventional  FT1000MP/WSJT6 system.
The two channels receive identical input at 28MHz from my
XV144 transverter.
The only significant difference lies in the Linrad dumb noise blanker
in the first, and the FT1000MP noise blanker in the second.

I had intended to wait a little longer - Joe is away travelling, I
think -
before posting any observations, so these are just preliminary.

1. Someone recently observed that MAP65-IQ did not seem to decode
anything weaker than -20dB. I thought that at first, but I have had
successful MAP65-IQ decodes now at -26dB.
However I still see WSJT decodes at (0 10) or better
of stable, weak signals when MAP65-IQ does not decode them at all.
By and large, when both channels decode successfully,
the reported signal strengths agree within 1dB.

2. It is my strong impression that MAP65-IQ does not like signals
weaker than -20dB which drift, say, 15Hz in a period, and
usually not a linear drift.
I find that the WSJT6 manual AFC will follow and decode such signals
when MAP65-IQ fails.
Conversely WSJT decodes stable weak signals better with AFC off.
MAP65-IQ only succeeds when the signals are stronger than about -20dB.

3. Occasionally I get an extraordinary decode from MAP65-IQ.
Recently I was monitoring Mike K6MYC calling an invisibly weak WP4CNU.
Mike's signal level was -11dB in both MAP65-IQ and WSJT6 - huge!
WSJT6 produced "WP4CNU K6MYC DM07".
MAP65-IQ gave "W44HMY QY2XRI AB78" for the same transmission.
None of those "words" are in my Call3.txt file.

I don't yet have any MAP65-IQ wave files, but I do have the ALL65.TXT
file.

Guy VK2KU

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