Jasen Betts wrote in a message to Roy J. Tellason:

 JB> Hi Roy.

 JB> 07-Jan-04 20:16:25, Roy J. Tellason wrote to all

 RJT> One is a chip resembling an op amp,  but apparently preconfigured
 RJT> as a unity-gain buffer.  I found it easily enough in my
 RJT> databooks, though I don't know why you'd get these and not just
 RJT> use a standard op amp and configure it as a unity gain part.
 RJT> Maybe some difference in the spec that's not apparent to me, or
 RJT> something...    (Anybody know?)   I suppose I'll think of
 RJT> something to do with these sooner or later

 RJT> The other part that jumped out at me as being a little unique was
 RJT> a 565 PLL chip.  I have heard of this one before,  but have *no*
 RJT> idea what you'd do with it.  Any of you guys have any thoughts on
 RJT> the matter

 JB> ISTR that a PLL is a kind of frequency follower, other than using
 JB> it in a frequency synthesiser (in a radio tuner) or frequency
 JB> multiplier etc I don't know what you could do with it,

Sounds about right.

 JB> HMM, maybe you've got a parallel-port radio tuner kit there. 

Could be...

I've been bumping into all sorts of circuits lately,  radio circuits among
them.  I'd like to know,  though,  how some stuff (scanners and other
things that deal with a *lot* of frequencies) manage it.  It's been quite
some time since I read anything on this subject,  but I remember early gear
that switched coils,  even to the extent of plugging different ones in, 
and I have my doubts that modern stuff does anything of the sort.

I suspect that this is where things start getting less into ordinary
"tech" stuff and more into that "black art" portion of
design that I've been avoiding all these years.  :-)

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