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[Linrad] Re: MAP65-IQ Issues


A number of people have "complained" that MAP65-IQ has some
significant bugs in it.
We need to remember that this is just a preliminary trial - an alpha
release - certainly not a beta release, and exactly for the purpose of
finding such bugs.
I am sure Joe will fix the major things as soon as he is able -
meanwhile we can live with them.

There are 2 separate calibration problems which have been mentioned,
and these deserve to be clarified.

1. Ned AA7A commented on a 4kHz discrepancy between the frequency
logged in the map windows and the actual frequency. Ned was using a
Linrad centre frequency of 144.130MHz.
I had also noted a similar discrepancy, but 14kHz in the opposite
direction, using a Linrad centre frequency of 144.112MHz.
This suggested to me a simple work-around which I tested successfully
Set your Linrad centre frequency to 144.126 (or 28.126), and the error
vanishes! :-)
Just a temporary fix until the coding bug is fixed.

2. Ned also commented that he was sometimes a whole kHz out when
clicking on the wide waterfall to select a frequency.
Let me explain by example.
For a nominal transmit frequency of, say, 144.125MHz, the sync pulses
are on 144.1262705, 1270.5Hz higher.
I am now used to clicking on the wide waterfall in Linrad to select a
signal, reading its frequency from the HiRes bandscope,
mentally subtracting about 1.3kHz, and setting my transceiver
I am not sure exactly what Joe has done in software, but I think he
has tried to line up the MAP65  wide waterfall with its scale in such
a way that the nominal carrier frequency is adjacent to the visible
sync pulses (in the absence of Doppler). So either the scale or the
waterfall is shifted about 1.3kHz.
I set my GPS-locked Signal Generator to 144.1263 to simulate the sync
pulse frequency from a 144.125MHz carrier (only 100Hz steps
This should, I think, put a line on the MAP65-IQ wide waterfall at
It's actual position was just below 144.124MHz (close to 144.1237).
It is as if the correcting shift has been applied twice, or perhaps
this is coincidence.
In any case, I think we have all by now learned to click on the MAP65
wide waterfall about 1kHz ABOVE the trace of sync pulses, in order to
identify the nominal carrier frequency, create the wanted narrow
waterfall, and set the transmitter frequency.

Guy  VK2KU

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