31.25 Hz tone detection with a 567 PLL tone decoder chip        18 Jan 2013
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Updated 20 Jan to suggest faster detections.

I had completely convinced myself that a 567 PLL tone decoder chip would NOT 
work for detecting the amalgamation of random phase 31.25 Hz  energy for 
detection of user presence in the passband because it was not coherent.  
And this was confirmed by responses from others.  

But then looking closer at KA3WCA’s test and Peter’s comments also indicated 
that in phase would occur now and then, so with a long enough HANG TIME, on
the 567 chip used as a narrow band tone detector, then it could work well 
enough by detecting even occasional coherent phase.

Tune it to 31.25 Hz +/- .25 and +/- worst case component drift and let 
detections re-trigger a 555 drop-out timer and Im done.  UPDATE:  Turns out
that setting the bandwidth that narrow drastically delays detections and since
KA3WCA's on0air tests show fades as rapid as one second, it is probably better
to widen the bandwidth and speed up the detections.  Besides, we want to 
detect anything in the passsband, so no need to be so narrow on the 31 Hz
component.

RADIATION:  WB4LNM says there are radiation problems with 567 and 555’s in 
space.  But PCSAT going on its 13th year in space is 100% dependent on the 
proper 1 minute retriggering of the critical 555 fail safe timer which powers
the TNC's and there have been no known problems in over 12 years in its 800km 
orbit during that time.
  
I’ll lead-shield the top and bottom of the 567 and 555 chips.

Objections?

Bob, WB4APR