Re: [Freetel-codec2] FreeDV 2020

Tue, 14 May 2019 15:42:45 -0700 

Hello Gerhard,

regardng phase noise measurements, close in...
If anyone is interested, I have a python script that takes an audio tone in a sound file and produces close-in phase noise calculations. I wrote this for when I produced a locking board for the IC9700 and needed to see what happened around 1 to 100 Hz.
yes, you can do this by inspection with Spectrum Lab, we had to compare a few different radios under many conditions, hence the script.
IC9700 locked : The 10Hz noise was about -62 at 144MHz, 1Hz noise about -45. Could be improved from the prototype. 

But measuring down below 5Hz is very difficult to do well.
certainly multplication up to 10 GHz makes things more difficult. maybe 40dB worse compared to 144 megs. 

glen


On 15/05/2019 8:07 AM, [email protected] wrote:
Hi, yes, I know about the main focus of mode 2020. I just want to promote this mode also for satellite, as it really will be a high quality audio mode and other DV modes are not allowed there because of the bandwith limit of 2700 Hz.
More tests will follow. But the problem not is Doppler shift, because QO-100 a stationary satellite over Africa with very slow drift around a fixed point. The problem rather is the thermal drift and jitter in local oszillators used for mixing microwave to "normal " frequencies.
Those mixers operate with fundamental crystals at around 25 to 40 MHz and so each drift or jitter is multiplied by a hugh figure. 
But this is not a problem only for DV, just for every digital mode.
LNBs on 10 GHz are therefore stabilized by OCXOs or GPSDO, and same has to be done on the TX side, although it is not as difficult as it is only 2,4 GHz. I have worked several stations in G, DL and PA in mode 1600 using the LimeSDR, only having a TCXO. Using other hardware (LimeSDR mini or Adalm Pluto on TX side or LNB with PLL or even TCXO on RX side) I have recognized, that Jitter of LO is quite a problem. Jitter could be around 20-50 Hz and that is makeing narrow band decoding impossible. 

Anyway, it is a very interesting an new field to investigate.

Regards

Gerhard OE3GBB


Am 14.05.2019 21:36, schrieb David Rowe:


Hi Gerhard,

Well done :-)  The first 2020 signals in Europe (and space)!

2020 is designed for HF channels with SNRs > 10dB with slow fading, the
sort of channel where SSB is an easy copy.  So it won't go as low as
700D.  On non-fading channels (like a satellite or UHF line of site) it
will go down to 3dB SNR with no errors.

The main focus of this project is the new, Neural Net codec.

The demodulator in 2020, like 700D, has a rather narrow frequency offset
acquisition range of +/- 20Hz. As you have found, will make getting sync
on a microwave or satellite channel difficult.

While it can track changing frequency offsets, it might not be able to
track something as fast as satellite Doppler.

-/-

This week I've fixed some problems with the Windows build, so will test
that this weekend and take a look at the sync bug next.

Cheers,
David

On 14/05/19 22:07, [email protected] <mailto:[email protected]> wrote:

Hi David,

Big success!

Freedv-gui-brad-2020 is running on Ubunti 18.04 on my new I5-8xxx. I am
having SNR 20 in mode 2020 in closed loop and on 20m to the websdr in PA
and G above S7 I got full decoding. Just QSB below S7 is kind of a
problem. Also tuning is not as easy as in the other modes. So I first
had to tune to mode 1600 and than switch to 2020. The audio was
connected by simple cables between the Linux and the PC running HPSDR.

Made also a first try for satellite work:

First I was using a LimeSDR-USB for transmitting on 2,4 GHz using
SDR-Console. I recognized a problem in the transmission chain as there
were interuptions in the audio in both modes 1600 and 2020. Never had
that before, but changed recently to the new Version 3.0.9 of
SDR-Console. Have to check again with earlier version.

I than changed to DATV-Express hardware and software for SSB. No
dropouts, good decoding on 2,4 GHz in mode 1600, but very difficult to
get the right tuning in mode 2020. But got SNR 16 in closed RF-loop
within the shack. I think at that frequencies the signal jitter and
thermal drift is quite serious. Will go on with TX to the satellite and
receive by WEBSDR with GPSDO control.

First part of tests over satellite no finished. DATV-Express-Card is
drifting to much and with LimeSDR I burned my preamplifier. So I fired
up my 70cm to 13cm converters. First one was from DX-patrol. This one is
also drifting too much and would need a change in hardware with external
reference. The other one is from SG-Labs. His one is quite stable, just
some jitter is to hear in CW. This one is having the possiblility for
having an external reference. Will now hook up the audio from freedv to
the FT-897 and go on with my tests.

I think it would be helpfull to have pilot tones in mode 2020, same as
in mode 1600, to scope with those unstabilities on microwave. A few
Hertz more in bandwith would not be any problem at this frequencies.

Audio quality was PERFECT!!

Thank you for your work. If I can help with further test, please let me
know. I am ready for skeds on shortwave now.

Regards

Gerhard OE3GBB




Am 12.05.2019 13:10, schrieb David Rowe:

    Hi Gerhard,
    Those sorts of messages to the Linux console are quite normal, just some 
    debug stuff the sound card library prints out.

    Cheers,
    David
    On 12/05/19 18:06, [email protected] <mailto:[email protected]> <mailto:[email protected] <mailto:[email protected]>> wrote: 

        Hi David,
        After installing freedv-gui-brad-2020 I wanted to configure a second 
        sound card. But I get following message:

        oe3gbb@oe3gbb:~/freedv-gui-brad-2020$ ./build_linux/src/freedv
        Server listening at 0.0.0.0:45116
        pos 1 1
        EXCHANGE_DATA_IN:
        g_nSoundCards: 2
        g_soundCard1InDeviceName: HDA Intel PCH: ALC892 Analog (hw:0,0)
        g_soundCard1OutDeviceName: HDA Intel PCH: ALC892 Analog (hw:0,0)
        g_soundCard1SampleRate: 44100
        g_soundCard2InDeviceName: Logitech USB Headset: Audio (hw:1,0)
        g_soundCard2OutDeviceName: Logitech USB Headset: Audio (hw:1,0)
        g_soundCard2SampleRate: 44100
        rxInAudioDeviceName: HDA Intel PCH: ALC892 Analog (hw:0,0)
        rxOutAudioDeviceName: Logitech USB Headset: Audio (hw:1,0)
        txInAudioDeviceName: Logitech USB Headset: Audio (hw:1,0)
        txOutAudioDeviceName: HDA Intel PCH: ALC892 Analog (hw:0,0)
        freedv_get_n_speech_samples(g_pfreedv): 2880
        freedv_get_speech_sample_rate(g_pfreedv): 16000
        ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM
        cards.pcm.rear
        ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM
        cards.pcm.center_lfe
        ALSA lib pcm.c:2495:(snd_pcm_open_noupdate) Unknown PCM
        cards.pcm.side
        ALSA lib pcm_route.c:867:(find_matching_chmap) Found no matching
        channel map
        ALSA lib pcm_route.c:867:(find_matching_chmap) Found no matching
        channel map
        ALSA lib pcm_route.c:867:(find_matching_chmap) Found no matching
        channel map
        ALSA lib pcm_route.c:867:(find_matching_chmap) Found no matching
        channel map
        fifoSize_ms: 440 infifo1/outfilo1: 19404 infifo2/outfilo2: 19404
        rxFifoSizeSamples: 3290

        I tried with two different USB headsets, result both the same.
        These are
        relatively old. Could that be the reason?

        Regards

        Gerhard OE3GBB




        Am 12.05.2019 08:08, schrieb David Rowe:

            Hello,

            There's been steady progress on FreeDV 2020 lately:

http://www.rowetel.com/?p=6747

            This weekend, a few of us around Adelaide had 2020 QSOs to
            get a feel
            for the "user factors".  There are a few bugs with sync and
            the Windows
            build left to work through.  Speech quality is very good.
            In other news, a team of Hams have been working on the software 
            engineering on Codec 2, in particular FreeDV 2020 and stm32:

http://www.rowetel.com/?p=6725

            Cheers,
            David


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