Hi all,
On the 700D spectra, Matt, there is a 25Hz "chop" that is broadening the
spectra.
In my "playing" here, modifying "freebeacon.c" to "parrot.c", a repeater, I use
a speaker to mic patch
and I hear the 25Hz clicking almost all the time.
My system here: Fedora 25 linux on an ASRock QC5000-ITX motherboard. (Low power)
lspci:
00:14.2 Audio device: Advanced Micro Devices, Inc. [AMD] FCH Azalia Controller
(rev 02)
My Pi system: Fedora 28 ARM, Banana Pi (original) with a 120Gb SATA SSD
lsusb:
Bus 002 Device 002: ID 08bb:2902 Texas Instruments PCM2902 Audio Codec
Behringer UCA202
But then, I'm having all sorts of software coding issues, not having "C" as my
first
programming language. Remember Algol or mini-gol from 1971.
Alan VK2ZIW
On Fri, 13 Jul 2018 07:09:17 -0500, Matt Roberts wrote
> Hi All,Earlier in the list, I had described finding a sound card thatseemed
> to work fine for the 1600 mode, but had some intermittenterrors on 700D, even
> on a very high SNR back-to-back test betweencomputers.
>
> I did some diagnostic recordings, comparing the device to one thatdoesn't
> present the same symptoms, and sent them to David. Heidentified a subtle
> difference between the behavior of the twodevices, and using that as a
> starting point, I have continued toinvestigate what exactly is the difference
> between the two devices-- and that investigation is still ongoing.
>
> However, during that conversation, I asked David a couple ofquestions that
> really belong on the list here, so I'm hoping Davidwill be willing to provide
> a little commentary on either or both ofthese:
>
* What details about the 700D mode's modem layer make it moredependent on
things like frequency linearity, frequencystability, phase stability, etc.,
above and beyond those ofolder modes like 1600?
* I noticed that the keying spectra of the 700D mode containsmuch more energy
outside the 1kHz to 2kHz frequency "envelope"than the 1600 mode did. I can't
post pictures to the list, butbelow are a couple of links to the different
measured spectra. Is the 700D mode dependent on having this additional
spectralenergy to demodulate the symbols properly? E.g., is thissimilar to the
difference between the hard-keyed RTTY spectrumdistribution vs. that of a
wave-shaped PSK signal? Or is theresome other reason why the mode appears
"broader"?
> 1600 Spectrum: http://www.kk5jy.net/snr-freedv/codec2-1600.png
>
> 700D Spectrum: http://www.kk5jy.net/snr-freedv/codec2-700D.png
>
> Thanks ahead of time to David for taking a look at these.
>
> 73,
> Matt
Alan
Evil flourishes when good men do nothing.
Consider the Christmas child.
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