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Article #7425Re: Voltage Controlled Xtal Oscillator
From: John Whitmore
Date: Tue, 25 Sep 1990 02:50
Date: Tue, 25 Sep 1990 02:50
31 lines
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1632 bytes
In article <935@hls0.hls.oz> geoff@hls0.hls.oz (Geoff Bull) writes:
>
>I want to build a 60 MHz VCXO.
>Can I simply replace the capacitor on a MC1658 VCO with a capacitor
>and crystal in series?
>
Not really. The 1658 is a multivibrator, and few (if any)
crystals will operate reliably with all the frequencies that it'll
be generating (it MIGHT work if you put a series LC in, to limit the
out-of-band power). Usually, one uses a damped crystal (put a resistor
across it if you have to), with a simple oscillator like
|
+-------------+
| |
| /
+--|O|--+---| NPN transistor
| | |
= = \
| | |
GND GND GND
Resistors omitted to confuse the neophytes.
(I hope the ASCII graphics isn't too terrible). Tuning would be by using
a varactor diode/capacitor combination for one of the two capacitors.
As nearly as I can remember, some crystals come specified for VCO
operation (usually very narrow band).
John Whitmore
Technical Details
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<8071@milton.u.washington.edu>Path:
arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!rpi!dali.cs.montana.edu!milton!whitReferences:
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Path: arc1-ca.pugleaf.net!utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!rpi!dali.cs.montana.edu!milton!whit From: whit@milton.u.washington.edu (John Whitmore) Newsgroups: sci.electronics Subject: Re: Voltage Controlled Xtal Oscillator Summary: Multivibrator is spectrally impure (not good for crystal) Keywords: Oscillators VCO VCXO Message-ID: <8071@milton.u.washington.edu> Date: 25 Sep 90 02:50:56 GMT References: <935@hls0.hls.oz> Organization: University of Washington, Seattle Lines: 31