[App_rpt-users] RTL_SDR for receive

[Bryan Fields]

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