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[Linrad] Re: MAP65-not-IQ display oddities and doesn't decode

I need to report some progress and some lack of progress.

Linrad running a Linux machine and sending unicast packets to MAP65
on a WinXP machine _almost_ works correctly.  It decodes signals after
the last fix, which involved reducing the level sent to the MAP65
program from a reported 23 dB to about 9 dB by reducing the
numerical value of  "First FFT amplitude" from 1000 to 200. 
Maybe some of the strong spurious had clipped in the calculations? 
The waterfall looks cleaner now as well.

MAP65 running on WinXP still has problems on the waterfall

    * Only displays spectrum from 105 to 155, centered on 125
          o Should display from about 70 to 170 kHz.
    * Labels at top 2.5 kHz off from spectral lines in waterfall
    * See the screen shot below


I don't know how MAP65 figures out how much spectrum width to give
to the waterfall...but it may have something to do with my PC not handling
96 KHz sound cards correctly.

Since I'm typing, I'll mention another Linrad configuration problem.
My setup only has one polarization, but MAP65 requires Linrad setup
for two polarizations.  I thought that might be a problem, so made an
audio splitter cable to feed the same Rx IQ output to both inputs
on the Delta-44 from the same audio source.  This second I/Q input
doesn't have perform correctly  with regard to image rejection
around 0 Hz.   It's as if the I and Q are shorted together or one
channel is missing, but I checked all that with an Ohmmeter.  I'm
using envy24control under Linux to configure the delta-44 and don't
see anything wrong.

Any ideas on any of this?

Leif Asbrink wrote:
> Hi Jeff,
>> My windows XP install does has a problem where it seems to want to
>> convert all audio to 48 kHz sampling rate.  For example using a sound card at 96
>> kHz in linrad only shows +/-24 KHz of active spectrum, the rest looks
>> filtered out.
> "a sound card" Do you know that the soundcard is capable of sampling 
> at 96 kHz? 
Yes the sound card definitely does 96 kHz.  The Win XP setup used to 
work correctly,
but something went wrong while installing various sound cards and 
un-installing them.
> As far as I have been able to find out, there is no way
> to find out hardware capabilities under Windows by quering the device.
> Linrad therefore allows you to set any sampling speed. Windows will 
> silently do the rate conversion in software. (When up-converting
> the increased bandwidth is of course totally useless.)
> I can not give the answers about map65, but you might press 'T'
> to get timing info in Linrad. On my laptop I can ask for 96000 Hz
> and Linrad evaluates it to 95350. When I ask for anything between
> 96100 and 97000 I get 96650 Hz. 
T reports a sampling speed of 96007 Hz.
> The fractional resampler does not
> allow finetuning of the hardware. Somewhere in the system settings you
> can change the quality of the resampler. Trade quality vs cpu load.
> I do not know if that could allow a finer stepping in the resampling
> ratio. In any case, MAP65 will require a reasonably correct sampling
> speed and not all soundcards deliver that.
> 73
> Leif / SM5BSZ
> >

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