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

James Washer washer at trlp.com
Sun Jan 1 21:29:04 UTC 2006


One last question... do you have a dual trace scope? If so, are the signals on pins 5 and 6 out of phase by 180degrees? My belief is that the chip is (attempting to) scale the signal on pin 6 by feeding back a signal 180 out of phase. The resistor between 5/6 sets the bias, the cap controls the amplitude.. but I want to make sure this is the case.

thanks

 - jim 

On Sun, 01 Jan 2006 07:24:19 -0600
Ron Tonneson <ronton at southslope.net> wrote:

> Jim,
> 
> Yes, it looks like it is above and below the 2.5v.  To measure the 0.1Vp-p I was AC coupled on the scope.  Kind of hard 
> to see and measure the p-p when DC coupled.  I agree it is a low signal but the TNC-X does a good job decoding.
> 
> Ron
> 
> James Washer wrote:
> > 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
> > 
> 
> 
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