9_MHz_LINEAR_VCO

Published:2009/7/6 0:43:00 Author:May | From:SeekIC

U1A and U1C of RCA CA3046 transistor array form emitter-coupled oscillator. Portion of U1A current is diverted through U1B and L1, producing magnetic flux that reduces effective inductance of resonating coil L2. Output frequency is varied in direct pro portion to voltage applied at A. L1 is 23 turns on 3/4-inch Teflon form 2 inches long, with 4 turns wound between windings for L2. VR1 is 1N3828 6.2-V zener. Circuit must be well grounded and shielded to avoid hum pickup by input, which could modulate output.-D. G. Stephenson, A Second Look at Linear Tuning, OST, March 1977, p 40-41.



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