[App_rpt-users] RTL_SDR for receive

Tue May 22 17:27:11 UTC 2018

Have you tried using the chan_usrp module?  It’s designed to work with GNU Radio.  I use it for bridging, but I’ve never tested it for this particular instance.  I’m reading with interest. 😊  73 de K4SQI!

Steve, K4SQI

From: KD2NFC, Joe Puma
Sent: Tuesday, May 22, 2018 1:23 PM
To: Users of Asterisk app_rpt
Subject: Re: [App_rpt-users] RTL_SDR for receive

I’m using a image. Not 100% sure where I got it. Might be David’s. I can post the config. What do want to see?

Yes the rtl_rm and aplay pipe will play on default sound device. The -D in aplay command portion of the command specifies your sound device.  Looks like the command I pasted had a double of the aplay command. It should read: 

rtl_fm  -M USB -f 446.160M -A fast -s 12K -p -0 -g 0.0 | aplay -r 12k -t raw

-D default:CARD=Loopback -c 1 -f S16_LE

I use to use this with wsjtx and the rtl-SDR for receive only and it piped the audio right into the program.  

The thing I need to accomplish is allow asterisk to use the usb fob for audio out and make use of the PTT and then allow input from another hardware device. I read that the only way to do it is using usbaudio driver for radio and adding a Alsa.conf file pointing to the input and output device you want to use. 

When I enable the chan_alsa.so and reboot, the radio keys up because the PTT is high from the usb audio activating but no audio comes from asterisk. It’s certainly not behaving the way should using when using chan_alsa.so by looking in the alsa.conf file and finding its audio in and out devices.  

Wondering how the usbaudio.so find it’s device. Does it assume the usb audio is card 0, or the default audio. What if you had two audio fobs on the system and you wanted to specify a specific one?

TBC.....

Joe
Kd2nfc

Sent from my iPad

On May 22, 2018, at 3:44 AM, Bryan Fields <Bryan at bryanfields.net> wrote:
On 5/22/18 3:29 AM, KD2NFC - Joe wrote:

I was trying to use a rtl-sdr to pipe a receive signal into the input or
receive audio for asterisk instead of using the mic in on the usb audio fob.

I've always done this using a usbradio or simpleusb based input, never using
the chan_alsa.  I don't believe alsa works for radio interfaces as there is no
signaling for PTT/COR/PL/etc.

Heres what I got so far. I can get a rtl-sdr installed in the Arch Linux by
using pacman -s rtl-sdr. 

If you're running arch you compiled allstarlink from source, so can you post
your config output?

Then if you run this command, it will pipe a FM 12Khz bandwidth centered on
446.160 mhz and pipe it to the loopback device which is the device name of
the loopback.

rtl_fm  -M USB -f 446.160M -A fast -s 12K -p -0 -g 0.0 | aplay -r 12k -t raw
-D default:CARD=Loopback -c 1 -f S16_LEaplay -r 12k -t raw -c 1 -f S16_LE

Does this work if you just output to the local speakers?

in modules.conf I enabled chan_alsa.so and after reboot with chan_alsa.so
loaded I get no audio at all. My radio keys up at bootup but I get no
initial greeting, no audio is coming through. Now I wasn't expecting this to
work of the top, I still need to figure out how the node is going to get cos
from the rtl-sdr, I could try to use ctcss but can anyone help me connect
the dots on this with what I have so far. 

I don't think you'll have the signaling here to make this work.   You might be
able to loop this into the DSP functions of USBradio, but it's going to need
some code to glue it together.

This sounds like a cool project, but GNUradio isn't the easiest to work with :)

73's
-- 
Bryan Fields

727-409-1194 - Voice
http://bryanfields.net
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