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- Path: sparky!uunet!news.larc.nasa.gov!grissom.larc.nasa.gov!kludge
- From: kludge@grissom.larc.nasa.gov (Scott Dorsey)
- Newsgroups: sci.electronics
- Subject: Re: Crystal-controlled FM XMTR?
- Date: 9 Nov 1992 16:45:33 GMT
- Organization: NASA Langley Research Center and Reptile Farm
- Lines: 21
- Message-ID: <1dm4jdINNgk0@rave.larc.nasa.gov>
- References: <1992Nov6.200359.27073@ms.uky.edu> <1992Nov6.204019.6938@news.nd.edu> <1992Nov9.033136.28608@athena.cs.uga.edu>
- NNTP-Posting-Host: grissom.larc.nasa.gov
-
- In article <1992Nov9.033136.28608@athena.cs.uga.edu> mcovingt@aisun3.ai.uga.edu (Michael Covington) writes:
- >In article <1992Nov6.204019.6938@news.nd.edu> fdeck@dumpster.helios.nd.edu (francis deck) writes:
- >>I've seen talk about one-chip FM transmitter circuits, but it
- >>appears they are all slug-tuned and experience frequency drift.
- >>Is there a simple circuit out there which is a monaural or
- >>stereo (doesn't matter for my application) FM transmitter,
- >>but which has a crystal timebase? I'd imagine it'd use some
- >>sort of PLL, but at 89 to 108 MHz, I'm lost. Any help?
- >
- >Hmmm, there isn't, but there should be. It's easy to "pull" a crystal
- >by using a (modulated) variable capacitance across it. To get enough
- >deviation to be audible on an ordinary FM radio, you'd probably want to
- >use a crystal at perhaps 1/27 the eventual frequency, and then triple
- >it several times (thereby also tripling the deviation).
-
- Yes, but you get lousy linearity this way. For better linearity your best
- bet is to generate your signal with a crystal oscillator, then phase modulate
- it with a seperate stage. You'll need to pre-emphasize the signal in order
- to get flat frequency response.
- --scott
-
-
