🚀 go-pugleaf

Funny that, I was just thinking about how I could record very *low*-
frequency signals on my regular old cassette deck and not have the result
sag all to hell because everything in the deck is AC coupled with a pitifully
small time constant.

I haven't started prototyping it yet, but I propose to use a PLL [XR2212
looks like a nice chip] with, oh, 6 to 8 KHz center freq for the VCO.  The
phase detector loop would be opened up for recording, and I'd just have 
the incoming signal sweep the VCO, and record the resulting FM on the tape.
For playback, re-connect the feedback loop and the error voltage would be
my demodulated output.  The VCO would need some kind of trimmer to zero
out any DC offset from a different tape deck with a different tape speed.

I realize that this doesn't help answer the medical probe problem, but if
some PLL wizard out there is going to address either one of these msgs,
what Huge Caveats should the builder be aware of??

_H*