Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!rutgers!topaz.rutgers.edu!hobbit From: hobbit@topaz.rutgers.edu ($ *Hobbit*) Newsgroups: sci.electronics Subject: Re: HELP: FM Recording of 300-3KHz channels on 50 KHz tape deck Message-ID: Date: 30 Jan 89 11:41:41 GMT References: <15020@oberon.USC.EDU> Organization: LCS Expert gang, Rutgers Lines: 18 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*