Larry you are correct about the theory and if two capacitors are used they must be balanced also. I have generally found that balance is not always what it seems and if secondary single or double fixed capacitor can be avoided then that is best but it sometimes is not avoidable. And stray capacitance from a bad layout can really through you off. It is just one of those things that has to be dealt with on a individual basis.
John, WA5BXO -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] Sent: Thursday, January 17, 2008 1:41 PM To: Discussion of AM Radio in the Amateur Service Subject: Re: [AMRadio] Home-brewing construction considerations SNIP: 1) A single capacitor plate-to-plate wound probably not upset the balance appreciably - in fact if the cap, and connections to it, were totally symmetric it wouldn't at all. The fixed vacuum caps I've seen have an outside and an inside cylinder, so stray capacitance to the surroundings from the outside cylinder would probably be larger than the strays to the inside cylinder. However, as long as the cap was reasonably spaced from surrounding stuff, I don't think it would be of any practical consequence on the lower bands where you'd be using the auxiliary fixed cap anyway. 2)If you were to use two caps, with a common connection tied to the rotor of the butterfly cap (you said stator - did you mean rotor?), their values would need to be double (not half) the value of a single cap, because they are effectively in series. ______________________________________________________________ Our Main Website: http://www.amfone.net AMRadio mailing list List Rules (must read!): http://w5ami.net/amradiofaq.html List Home: http://mailman.qth.net/mailman/listinfo/amradio Help: http://mailman.qth.net/mmfaq.html Post: mailto:[email protected] To unsubscribe, send an email to [EMAIL PROTECTED] with the word unsubscribe in the message body.
