Topics

UDRC-II as a Soft TNC

Edouard Lafargue
 

   Just got a UDRC-II to build a software TNC on a RPi3 using Direwolf and the Linux AX25 stack. Once I got over the initial disappointment of realizing the audio drivers were not in the mainstream kernel, I worked on the configuration last night and everything seems to be working fine, I have a working TNC and I can connect to the local packet network and BBS. Yes, I have read the various posts on why those drivers are not mainstream yet, just hoping the code will make its way into the kernel eventually.

That said, the way the connectors work is very confusing to me. Would it be possible to confirm that I understand the way the UDRC-II works properly:

  • The UDRC-II is basically a stereo sound card for both audio input and output.
  • The left audio output channel "LOUT" is mapped to the VGA connector only
  • The right audio output channel "ROUT" is mapped to both the VGA connector and the Mini-DIN connector pin 1, "TONEIN".
  • The left audio input channel "LIN" is mapped to VGA + the 1200 baud pin 5 on the Mini-DIN (AFOUT)
  • The right audio input channel "RIN" is mapped to VGA + the 9600 baud pin 4 on the Mini-DIN (DISCOUT)

  This is where it gets very confusing - if my radio DIN port is set in 1200 baud mode, this means that audio is getting into the UDRC through the Left In channel, and out through Right out, and through Right in and Right out if the radio is in 9600 baud mode. How shall I configure Direwolf in both modes then? From experimentation, I need to use "CHANNEL 1"  on my Direwolf configuration to make things work.

  Typically, I would love to see Direwolf/alsamixer examples for:

  • One radio: 1200 baud radio connected on either Mini-DIN or VGA
  • One radio: 9600 baud radio connected on either Mini-DIN or VGA
  • Two radios: One 1200 baud radio on Mini-DIN, one 1200 baud radio on VGA - or can both be using the VGA cable using a custom pinout?
  • Two radios: One 1200  baud radio on Mini-DIN, one 9600 baud radio on VGA
  • Two radios: One 9600 baud radio on Mini-DIN, one 1200 baud radio on VGA
  • ... you see the idea : basically, the various combinations that can be built/supported

   A related question is on how Direwolf treats audio out: does it transmit on left and right channels separately, or is audio out down mixed to mono and sent to both lines at the same time?

   I can't help but think I'm missing something there - is there a way to have two independent packet radios connected to UDRC-II ? Are some of the mappings handled at the Alsa mixer level? Any advice/explanation would be most welcome :)

Thanks,


Ed

 

Your general understanding is correct.  

The right way to handle two radios is to use a separate cable for each as documented at https://nw-digital-radio.groups.io/g/udrc/wiki/UDRC%E2%84%A2-II-Cabling-For-2-radios

We have also been experimenting with some asound.conf settings to give you two virtual mono sound cards. It works fine for direwolf, but not for dstarrepeater (the dstarrepeater software needs some modification to discover the virtual ports) -- but we are not quite ready to publish it.

Item 5.1.2 from https://nw-digital-radio.groups.io/g/udrc/wiki/UDRC%E2%84%A2-and-Direwolf-Packet-Modem#UDRC%E2%84%A2-II is a description of how to configure two radios using the two ports.

The audio is independent for the two channels.

On Fri, Oct 21, 2016 at 10:51 AM, <ed@...> wrote:

   Just got a UDRC-II to build a software TNC on a RPi3 using Direwolf and the Linux AX25 stack. Once I got over the initial disappointment of realizing the audio drivers were not in the mainstream kernel, I worked on the configuration last night and everything seems to be working fine, I have a working TNC and I can connect to the local packet network and BBS. Yes, I have read the various posts on why those drivers are not mainstream yet, just hoping the code will make its way into the kernel eventually.

That said, the way the connectors work is very confusing to me. Would it be possible to confirm that I understand the way the UDRC-II works properly:

  • The UDRC-II is basically a stereo sound card for both audio input and output.
  • The left audio output channel "LOUT" is mapped to the VGA connector only
  • The right audio output channel "ROUT" is mapped to both the VGA connector and the Mini-DIN connector pin 1, "TONEIN".
  • The left audio input channel "LIN" is mapped to VGA + the 1200 baud pin 5 on the Mini-DIN (AFOUT)
  • The right audio input channel "RIN" is mapped to VGA + the 9600 baud pin 4 on the Mini-DIN (DISCOUT)

  This is where it gets very confusing - if my radio DIN port is set in 1200 baud mode, this means that audio is getting into the UDRC through the Left In channel, and out through Right out, and through Right in and Right out if the radio is in 9600 baud mode. How shall I configure Direwolf in both modes then? From experimentation, I need to use "CHANNEL 1"  on my Direwolf configuration to make things work.

  Typically, I would love to see Direwolf/alsamixer examples for:

  • One radio: 1200 baud radio connected on either Mini-DIN or VGA
  • One radio: 9600 baud radio connected on either Mini-DIN or VGA
  • Two radios: One 1200 baud radio on Mini-DIN, one 1200 baud radio on VGA - or can both be using the VGA cable using a custom pinout?
  • Two radios: One 1200  baud radio on Mini-DIN, one 9600 baud radio on VGA
  • Two radios: One 9600 baud radio on Mini-DIN, one 1200 baud radio on VGA
  • ... you see the idea : basically, the various combinations that can be built/supported

   A related question is on how Direwolf treats audio out: does it transmit on left and right channels separately, or is audio out down mixed to mono and sent to both lines at the same time?

   I can't help but think I'm missing something there - is there a way to have two independent packet radios connected to UDRC-II ? Are some of the mappings handled at the Alsa mixer level? Any advice/explanation would be most welcome :)

Thanks,


Ed




--


John D. Hays
K7VE

PO Box 1223, Edmonds, WA 98020-1223
   

Edouard Lafargue
 

Thanks John!

I will take a closer look at my radio (Kenwood TM-V71A) since it looks like I'm receiving audio on both 1200 and 9600 irrespective of the menu settings somehow.

Something else I have noticed, is that every packet direwolf sends is looped back on the input, which should not happen - at least it does not happen on other audio interfaces I have used earlier. I have seen this on interfaces with coupling/grounding problems though.

Edouard Lafargue
 

More to the point: with the default UDRC settings, with radio off or even with the cable disconnected, there is definitely some loopback effect on the interface as you can see on the direwolf log when sending a UI frame: the first line is direwolf sending the frame, the rest if direwolf hearing the same frame on the audio input:

[1L] W6ELA>INFO:test<0x0d>

W6ELA audio level = 0(0/0)   [NONE]   |||:_____

[1.1] W6ELA>INFO:test<0x0d>


 

Engineering is looking into this, it can be duplicated.  Engineering will followup with a posting.

On Fri, Oct 21, 2016 at 1:30 PM, <ed@...> wrote:

More to the point: with the default UDRC settings, with radio off or even with the cable disconnected, there is definitely some loopback effect on the interface as you can see on the direwolf log when sending a UI frame: the first line is direwolf sending the frame, the rest if direwolf hearing the same frame on the audio input:

[1L] W6ELA>INFO:test<0x0d>

W6ELA audio level = 0(0/0)   [NONE]   |||:_____

[1.1] W6ELA>INFO:test<0x0d>



--


John D. Hays
K7VE

PO Box 1223, Edmonds, WA 98020-1223
   

 

OK I have gotten back on the bench and confirmed that there is no loopback at the analog level, but I have seen this before with Direwolf.

I just picked up a TM-V71A for testing.

Bryan K7UDR

On Oct 24, 2016, at 9:25 AM, John D Hays - K7VE <john@...> wrote:

Engineering is looking into this, it can be duplicated.  Engineering will followup with a posting.

On Fri, Oct 21, 2016 at 1:30 PM,  <ed@...> wrote:

More to the point: with the default UDRC settings, with radio off or even with the cable disconnected, there is definitely some loopback effect on the interface as you can see on the direwolf log when sending a UI frame: the first line is direwolf sending the frame, the rest if direwolf hearing the same frame on the audio input:

[1L] W6ELA>INFO:test<0x0d>

W6ELA audio level = 0(0/0)   [NONE]   |||:_____

[1.1] W6ELA>INFO:test<0x0d>



-- 


John D. Hays
K7VE

PO Box 1223, Edmonds, WA 98020-1223
   

Edouard Lafargue
 

  Thanks Bryan! I'm using a V71A as well, let me know if there is anything you'd like me to test on my sidel.​ I wonder if this might be something happening at mixer level in the audio codec chip...

Ed

Edouard Lafargue
 

Following up on this very old post :)
 
  I am still hitting the loopback issue on my UDRC-II - whether a radio is connected to any of the ports or not, I hear my own packets on the input of the UDRC-II.
 
   On the NW Digital Radio side, have you made any progress on this issue?
 
73 

 

Verify your configuration for channel 0 and 1 in direwolf. 

On Jun 16, 2017 16:53, "Edouard Lafargue" <ed@...> wrote:
Following up on this very old post :)
 
  I am still hitting the loopback issue on my UDRC-II - whether a radio is connected to any of the ports or not, I hear my own packets on the input of the UDRC-II.
 
   On the NW Digital Radio side, have you made any progress on this issue?
 
73 

 

We have a software engineer digging into this a bit deeper. 

On Jun 16, 2017 16:53, "Edouard Lafargue" <ed@...> wrote:
Following up on this very old post :)
 
  I am still hitting the loopback issue on my UDRC-II - whether a radio is connected to any of the ports or not, I hear my own packets on the input of the UDRC-II.
 
   On the NW Digital Radio side, have you made any progress on this issue?
 
73 

Edouard Lafargue
 


  Oh very interesting - I am using a radio connected to the DIN6 connector, so I have to use Channel 1 to connect to the AX25 stack in KISS mode. I had left Channel 0 unconfigured on direwolf.conf . When configuring Channel 0 for 9600 baud and 'N0CALL' for the callsign, then I don't hear my packets anymore.

   While I'm happy about this, I'm not 100% sure of what that is? Can you explain further, John?

Ed

Previous Topic Next Topic