View single post by sparks
 Posted: Nov 20th, 2013 05:34 PM
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sparks



Joined: Jan 15th, 2008
Location: New Zealand
Posts: 77
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I didnt need extra varicaps as I was controlling the receiver's built-in varicaps via the tune line that is controlled by the synthesizer. Ive done this method with several radios. In the radio shack "ghost boxes", this line is labelled VT. The synth output needs to be disconnected from the varicap line, so it can be swung with external DC control. Yes, with some varicaps, they need up to 30v to get into the small capacitance end of the range.
In medium wave sets that I did add varicaps to, I used to use BB212 varicaps. Theres 2 in one package, and have high capacitance per diode (500pF). For FM, I used BB204, also a double.
JEFF

P.S:
BB212 is a Philips part. I also used a Motorola varicap, MVAM109. Maybe more available in the USA.

Last edited on Nov 20th, 2013 07:51 PM by sparks