[App_rpt] USB Radio Interface

[Steven Henke]

Dave,

Good idea about using the transistor. I also use a short piece of wire wrap
wire to get to the pins.

It is fun soldering to those points. Luckily they are on corner pins and in
the case of the current batch of green USB adapters the COR point (VOLDN)
has a big pad.

Of course you could just buy one of the new URI devices (
http://www.dmkeng.com/Products.htm)   :)
73,
Steve Henke, W9SH
On Fri, Feb 15, 2008 at 1:44 PM, David Powell-Williams <
dpowellwilliams at shaw.ca> wrote:

> A general FYI to those contemplating use of the USB FOB interface with COS
> generated by hardware, as opposed to dsp:
>
> I found that my receiver did not drop its COS line all the way to ground
> potential in the no signal condition.  I presume the Schottky diode (CM108
> pin 48) was specified due to its inherently low junction voltage.
>  However,
> in my case, the receiver COS still did not drop low enough to generate
> switching.
>
> I replaced the Schottky diode with an NPN transistor (collector to CM108
> pin
> 48, emitter to ground, base to the receiver COS source through 10K).  Of
> course, this introduces a COS polarity inversion with respect to the
> CM108.
> The inversion is corrected by changing the 'carrierfrom=<usb | usbinvert>'
> polarity selection in usbradio.conf.
>
> One further point:
> The pin spacing on the CM108 is 0.5 mm. The wire diameter of resistors and
> diodes is about 1 mm.  I found it easier to attach 28 AWG wire-wrap wires
> to
> the chip, nail down the wires with hot-melt glue and attach the specified
> components to the far ends of the wire-wrap.
>
> Finally, soldering to the CM108 is best done before coffee.
>
> 73,
> Dave
> VE7MQ.
>
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