[App_rpt-users] CM119 USB interface

Kevin Custer kuggie at kuggie.com
Mon Dec 24 02:29:08 EST 2018


Brian,

If the application reports 999, my guess is you aren't inputting raw 
discriminator audio into the interface.  If the audio you are inputting 
into your radio interface has been Low Pass Filtered or is squelch 
gated, you cannot use DSP for noise squelch detection.   The application 
will tell you if there is sufficient squelch noise to utilize DSP noise 
squelch detection after you do the "radio tune rxnoise" command. If it 
fails, the audio type, amount, or quality isn't sufficient for DSP noise 
detection.

When fed with good discriminator audio, the noise squelch detection in 
app_rpt is nearly as good as a Motorola M6709 (analog) squelch chip, 
commonly thought to be the high water mark in noise squelch detection.  
999 is the total absence of noise, and is the result one would expect 
with a full quieting signal, or an inappropriately muted RX audio line.

Kevin W3KKC



On 12/23/2018 7:28 PM, Brian G wrote:
> Hi all, Merry Christmas
>
> My local club is working on setting up a few ASL nodes, and I've been 
> busy modifying some CM119 based USB sound cards to control the radios. 
> I'm using this card/dongle: 
> https://www.amazon.ca/Syba-SD-CM-UAUD-Adapter-C-Media-Chipset/dp/B001MSS6CS
>
> I've done several so far and have a few nodes working great with CTCSS 
> carrier detect. One issue I'm consistently running into, is when 
> setting the "RX Squelch Level" in the radio-tune-menu, it detects the 
> current RX signal strength as 999. This results in the inability to 
> use anything other than CTCSS for carrier detect. I can make plain old 
> VOX work too, but it results in considerable (2 sec+) hang time.
>
> Using DSP carrier detect won't work because it's impossible to set the 
> squelch high enough (max value 999). It always thinks there's a signal 
> present when there isn't. This happens regardless of whether there's a 
> radio connected to the dongle or not. As a matter of fact it happens 
> even when plugging in an unmodified dongle right out of the package. I 
> need it to work with no CTCSS. VOX would be fine if it wasn't for the 
> hang time, but would rather use the DSP option in usbradio.conf.
>
> I assume it's just the nature of the beast, and if I want it done 
> properly I need an adapter and radio capable of COS. But maybe someone 
> knows if there's something that can be done or not? Anyone have any 
> insight on how to either eliminate the VOX hang time, or eliminate 
> that "invisible" signal? I might be overlooking something. Thanks for 
> reading!
> --
> Brian - VA3DXV

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