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[aprssig] Waveform (signal) on MX614 RXIN pin?

James Washer washer at trlp.com
Sun Jan 1 05:29:50 UTC 2006


Wow! thanks for the quick response. Are you seing true sine waves above the 2.5Vdc bias?

Hmmm, 0.1Vp-p, that's quite small, amazing it can pick the signal out of that... 

I'll have to break out my signal generator tomorrow and see what I can get it to do. All testing thus for has been trying to copy off the air, which can be a real pain without a storage scope..

 - jim

On Sat, 31 Dec 2005 22:16:44 -0600
Ron Tonneson <ronton at southslope.net> wrote:

> Jim,
> 
> I have a TNC-X that uses that chip.  The schematic is here: <http://www.tnc-x.com/media/schematic.gif>.  Pin 5 is at 2.5 
> VDC with about .1 volt peak to peak ac when a packet signal is present.
> 
> Ron - K0QVF
> 
> James Washer wrote:
> > I'm working on a TNC based on an MX614. I'm not seeing anything useful on the RXD pins, so I took a look at the RXIN pin. The waveform there is most interesting. There's about 2Vdc bias. Further, signals get clipped at the 2V, I see the bottom halves of the sine waves below this 2V clipping, but never anything above it.
> > 
> > I'm wondering if any of you have both a scope AND a working MX614 tnc and could tell me what you see on pin 5.
> > 
> > This may be normal behaviour, caused by the tie between pins 5 and 6(RXAMP), but since I've never seen anything like this before, I'm just not sure.
> > 
> > 
> > THANKS and happy new year.
> > 
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> 
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