Made a little progress today…
I was able to listen to the audio piped from the rtl_sdr on the node today. Well I actually had to create an extension that opens the other end of the loopback device I am piping the audio into. I made an extension and it can be called up. I’m basically using alsa as a end point.
I guess for now it could be used to play noaa weather or any other frequency you want to sit it on. Rtl_fm has some cool features like you can add a few frequencies and rtl_fm will scan through them while its running. There could be an issue with squelch though, if there is a lot of noise it could keep the node keyed up and the squelch feature in the rtl_fm is quirky, it doesn’t cut the noise floor out weird.
Now that I have confirmed a working setup that audio can come into ASL from the SDR and learned a little more about this beast Asterisk I can figure out next steps. It wont be this way lol, we would need a Alsa type driver we can call from rtp.conf. Mike KB8JNM mentioned look into usrp. From some brief looks at it and I found that you can split the rxchannel and txchannel in rtp.conf. so what if I txchannel = UsbRadio/usb46596 and rxchannel = USRP/127.0.0.1:34001:32001. I don’t know much about usrp so I will have to see how I can pipe the audio of the SDR into that channel. To be continued….
So if you want to add a sdr dongle to your node just follow these steps. Don’t forget to plug in your rtl-sdr dongle 
Install the rtl-sdr drivers like I mentioned in the original post. I compiled the keenerds version as he have some bells and whistles in his build.
Add these commands to rc.local, they will setup the loopback and get rtl_sdr piping audio to the loopback. Check the frequency (-f ) to whatever you like, you can 146125000 syntax as well.
modprobe snd-aloop ; <-put this before asterisk loading
rtl_fm -M fm -f 145640000 -s 30000 -r 12k -g 3.0 | aplay -r 12k -D default:CARD=Loopback -c 1 -f S16_LE & ; <-put this after asterisk loads
create a alsa.conf in /etc/asterisk/
add this…
[general]
autoanswer=yes
context=local
extensions=s
language=de
input_device=hw:1,1,0
output_device=hw:1,0,1
I’m using usbaudio for this in rpt.conf but you have to enable chan_alsa.so in modules.conf
Next create a file called console.conf in the /etc/asterisk directory
Add this…
[default]
input_device = default
output_device = default
autoanswer = yes
context = default
extension = s
callerid = Radio Console KD2NFC <(0049) 123456789>
language = en
overridecontext = no
mohinterpret = default
active = yes
I can connect with my sip device by adding this to my extentions.conf
[dialplan]
exten => 222,1,Authenticate(1234) ; use password 1234 to connect or comment out this and the playback line below, you have to renumber the order.
exten => 222,2,Playback(access-granted)
exten => 222,3,Dial(Console/default)
exten => 222,n,Hangup()
If you add it to a dialplan context setup to work with your node you can get to it by doing a autopatch. Rpt fun <yournode#> *6222
Or dial 222 with your sip or iax endpoint. Make sure their contexts points to the dial plan with the extension you added.
Joe
Kd2nfc
···
From: App_rpt-users app_rpt-users-bounces@lists.allstarlink.org On Behalf Of Stephen - K1LNX
Sent: May 22, 2018 1:40 PM
To: Users of Asterisk app_rpt app_rpt-users@lists.allstarlink.org
Subject: Re: [App_rpt-users] RTL_SDR for receive
Are you trying to send RX audio to the simpleusb channel driver? You could always “force” the RPT_RXKEYED variable by issuing rpt setvar nodenumber RPT_RXKEYED=1 at the CLI to pipe audio through without having anything connected. I’ve done this for testing purposes to assert COS and works as intended. Not sure how you would be able to automate it however, maybe something in cron at boot?
Just thinking out loud… I too am interested in the progress of this as I’ve been wanting to mess with chan_alsa for a while, but never got started with it.
73
Stephen
K1LNX
On Tue, May 22, 2018 at 1:27 PM, Steven Blackford kb7sqi@gmail.com wrote:
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@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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