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

Ron Tonneson ronton at southslope.net
Sun Jan 1 04:16:44 UTC 2006


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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