On 9/15/07, Stephen Rodgers <hwstar@rodgers.sdcoxmail.com> wrote:

Steve Henke, W9SH, and Jim Dixon have completed the coding of a new
channel driver for asterisk named chan_usbradio.c which allows app_rpt
to work with modified USB sound fobs based on the CM108 chip. There is
an initial write up about this new hardware interface on my site at
http://app-rpt.qrvc.com/usbsoundfob.html.

The USB channel driver has DSP code in it for CTCSS detection and
generation, squelch, pre-emphasis and de-emphasis, audio level setting,
and soft limiting. You only need to make 3 connections to a repeater.
Discriminator audio, transmit audio. and PTT. A COR input is supported,
but not required.

The hardware is really inexpensive! USB sound fobs can be bought for
$7.95 at places like geeks.com. You will need 3 resistors, a Shottky
diode, and an NPN transistor in order to complete the modification.

A schematic detailing the modifications and pictures of the USB sound
fob before and after modification are posted on at the URL above.

I am working on a set of detailed modification instructions with
pictures so that those who want to use this interface can modify
the USB sound fob themselves.

Have Fun!

Steve Rodgers, WA6ZFT
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