Planning to make tests of FreeDV

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Jean-Baptiste GALLAUZIAUX

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Jul 8, 2022, 8:04:43 PMJul 8
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I plan to test FreeDV 1.8.0 on my portable station and need some advices.
My station is made of a SDR XCVR Hermes Lite 2 HL2 working with Quisk v.4.2.2 and an Alexloop  magnetic loop. My QTH is in New Caledonia, a South-West Pacific island at about 2000km from Australia and New Zealand.
The HL2 is a QRP rig, transmitting around 4 to 5 Watt and on the 20 meter band the efficiency of the Alexloop is around 46%, which means only 2 Watt are radiated.
What do you recommend as "mode" to be used with such a low power? FreeDV shows various choices : 700C, D,E or 800XA or 1600 or 2400B or 2020 or 2020B, which mode should I choose?
73 - Pierre - FK8IH

Mooneer Salem

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Jul 8, 2022, 9:58:05 PMJul 8
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Hi Pierre,

I have a compromised antenna setup at home too (MFJ magnetic loop) and I typically use 700D as it's the narrowest supported one. This helps make the most use of the radiated power, IMO.

Thanks,

-Mooneer K6AQ

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Jean-Baptiste GALLAUZIAUX

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Jul 9, 2022, 3:34:44 AMJul 9
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Thanks Mooneer. Another question : is it necessary that the two stations are using the same mode or can one choose one mode and the other another mode and the contact still being working?
73 - Pierre - FK8IH

Al Beard

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Jul 9, 2022, 4:00:28 AMJul 9
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Hi Jean,

Please please, please announce your presence by logging into qso.freedv.org

My 40m transmission "freebeacon" with ident every 5mins or so should reach you.

Presently around 20W mode 700D on 7063 KHz LSB.

If my "freebeacon" receives "//" in your Txt Msg, it will trigger a response.

Also look for your signals on some of the SDR receivers out there.


QF56IF   (Western Sydney, NSW)

Alan VK2ZIW

On Sat, 9 Jul 2022 00:34:44 -0700 (PDT), Jean-Baptiste GALLAUZIAUX wrote
> To view this discussion on the web visit https://groups.google.com/d/msgid/digitalvoice/fc5c6d5c-6870-44e3-8711-038348be2cfen%40googlegroups.com.


---------------------------------------------------
Alan VK2ZIW
Before the Big Bang, God, Sela.
OpenWebMail 2.53, nothing in the cloud.

Al Beard

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Jul 9, 2022, 6:38:22 AMJul 9
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Hi Jean and all,

I've just confirmed, my websdr can decode FreeDV mode 700D in either USB or LSB.
Tested on 7063KHz LSB.

On the GUI you'll notice two buttons [FreeDV] and [FreeDV] then look at the bandwidth
indicator above your frequency on the GUI to determine LSB or USB.

 The software mod was super simple (once I found it!). Simply add another mode
AnalogMode(
            "freedvB", "FreeDV", bandpass=Bandpass(300, 3000), requirements=["digital_voice_freedv"], squelch=False
),
and in the previous "freedv" line, change 300 to -300 and 3000 to -3000.

0x73

Alan VK2ZIW

On Sat, 9 Jul 2022 18:00:18 +1000, Al Beard wrote

Mooneer Salem

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Jul 9, 2022, 10:54:48 AMJul 9
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Hi Pierre,

By default multiple receive is on, which makes it so that the other person will automatically decode whatever mode the transmitting station's using without it needing to be explicitly selected. It'll also let you switch transmit modes without needing to restart the session. You can verify that this is enabled on your end by going to Tools->Options->Modem and making sure that "Simultaneously Decode All HF Modes" is checked.

Thanks,

-Mooneer K6AQ

Jean-Baptiste GALLAUZIAUX

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Jul 9, 2022, 6:24:41 PMJul 9
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Thanks to all. I get a clearer idea about FreeDV now with the manual and your advices and found all the needed settings (simultaneous decode all HF modes - a way to shift from LSB to USB...). As I only use my QRP station in portable mode I will check qso.freedv.org before leaving home and make tests during one or two hours in the chosen location, starting with VK2ZIW. Unfortunately I cannot use my station at home, which is a steel reinforced concrete building, just a "Faraday cage"! About VK2ZIW, the theoric efficiency of my Alexloop on 40M is 7%, which means I will radiate only 0.3Watt, I should receive well but I wonder if I can be heard!
73 - Pierre - FK8IH

Mooneer Salem

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Jul 10, 2022, 2:02:03 AMJul 10
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A lot of the effort for QRP communications comes from the person at the other end, too :) 

Also, I'm not 100% sure what the AlexLoop uses but from photos on DX Engineering it seems like it's LMR400 or similar coax. There might be a little bit more efficiency to be gained by going with thicker coax, if possible. Something to research later, anyway.

-Mooneer K6AQ

Al Beard

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Jul 10, 2022, 2:37:20 AMJul 10
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Hi Mooneer,

In "openwebrx" to do FreeDV demodulation, 8K audio samples are fed to "freedv_rx 1600 - -" so how do we
enable "multiple mode" decode?

(I modify this to "freedv_rx 700D - -") and mention this mode on the OpenWebRX title line.

Alan VK2ZIW

On Sat, 9 Jul 2022 07:54:34 -0700, Mooneer Salem wrote

Jean-Baptiste GALLAUZIAUX

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Jul 10, 2022, 3:44:17 AMJul 10
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Mooner,
The cable used with the Alexloop looks like an excellent and quite rigid (holding well its loop shape of 3 feet diameter) 1cm diameter coax made in Brazil of the brand DLC213  Cabo Coaxial DLC 213 Premium - [PDF Document] (vdocuments.net)
73 - Pierre - FK8IH

Mooneer Salem

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Jul 10, 2022, 3:59:35 AMJul 10
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Hi Pierre,

Based on the loss figures in the datasheet for DLC213 it seems pretty similar to LMR400 in terms of attenuation (https://www.timesmicrowave.com/DataSheets/CableProducts/LMR-400.pdf). The next step up would be LMR600, which based on the datasheet has about half the attenuation in exchange for being ~50% wider.

Anyway, the AlexLoop probably nailed the portability/loss tradeoff pretty well given how many people seem to use it :)

Thanks,

-Mooneer K6AQ

Mooneer Salem

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Jul 10, 2022, 4:01:44 AMJul 10
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Hi Alan,

That's a freedv-gui feature, but you can approximate it by calling freedv_rx repeatedly for each desired mode and selecting the mode that (a) syncs and (b) produces the highest SNR. Most modes use 8K sampling rate except for 2020/2020B which use 16K.

Thanks,

-Mooneer K6AQ

Jean-Baptiste GALLAUZIAUX

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Jul 11, 2022, 1:38:07 AMJul 11
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Mooner, Yes I keep the Alexloop as provided by its builder. I can put inside the Alexloop backpack all the items necessary for portable operation : the Alexloop, a tripod, the HL2 tranceiver, an EFHW antenna with its transmatch if I want to use a large band antenna, a 13.5 V/3.5Ah LiFePo battery, the iambic paddle, USB headset with mike... and the laptop computer has its own bag. This battery gives me around 5 hours of operation, more than the computer on battery!
73 - Pierre - FK8IH

Al Beard

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Jul 14, 2022, 10:00:01 PMJul 14
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Hi Mooneer,

Can I ask the question again?

We'd like OpenWebRX to be able to decode multiple Codec2 modes.

So, how does the FreeDV app achieve this?

Then, do we need an another command line app written with this capability?

(OpenWebRX concatenates various command line apps to achieve demodulation.
It's easy to change as it's all written in Python.)

Alan VK2ZIW

On Sun, 10 Jul 2022 16:37:10 +1000, Al Beard wrote

Mooneer Salem

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Jul 15, 2022, 12:27:31 AMJul 15
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Hi Alan,

I'm not sure a new command line application is needed but you can take a look at https://github.com/drowe67/freedv-gui/blob/master/src/pipeline/TxRxThread.cpp#L116 to see how the TX/RX audio processing pipelines get created. The actual part of the pipeline that deals with audio encode/decode (including multiple RX) gets created at https://github.com/drowe67/freedv-gui/blob/master/src/freedv_interface.cpp#L542 (which is referenced by TxRxThread.cpp).

Thanks,

-Mooneer K6AQ



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