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Amateur Radio Antennas - For discussion of all amateur band designed antennas and related accoutrements. This includes base, handheld, mobile and repeater usage. For commercial antennas on the amateur bands please use Commercial Radio Antennas below.

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Old 02-23-2018, 4:11 PM
   
Join Date: Oct 2015
Posts: 2
Default Balanced capacitors

I have a question thats been on my mind for a while.
I have been thinking of constructing a balanced atu to feed an hf doublet, of this configuration http://www.somis.org/bbat_f2.jpg

I do have two nice, identical roller coaster inductors I can use, but do not have a "balanced" butterfly capacitor.
However I have some vacuum caps of suitable value.
My question is, just how important is physical symetry for a capacitor in this sort of circuit, because surely, a vacuum cap is not of balanced, symetrical construction, as is a butterfly capacitor !
Then again, most magnetic hf loops use such caps, but maybe its because the feed system is NOT symetrical in this case.

Hints anyone ?
Thank you.
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Old 02-23-2018, 11:10 PM
prcguy's Avatar
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Join Date: Jun 2006
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Default

The capacitor in the link is not balanced but it must be insulated from everything around it, so any variable capacitor of sufficient voltage and capacitance rating will work.

After looking over the diagram and instructions I think you should find a better version of this type of project because the author is somewhat clueless. His choice of a "balun" claiming 30 to 33ft of coax wound around a PVC pipe will choke 1.8 to 30MHz is absurd.
prcguy



Quote:
Originally Posted by panserv View Post
I have a question thats been on my mind for a while.
I have been thinking of constructing a balanced atu to feed an hf doublet, of this configuration http://www.somis.org/bbat_f2.jpg

I do have two nice, identical roller coaster inductors I can use, but do not have a "balanced" butterfly capacitor.
However I have some vacuum caps of suitable value.
My question is, just how important is physical symetry for a capacitor in this sort of circuit, because surely, a vacuum cap is not of balanced, symetrical construction, as is a butterfly capacitor !
Then again, most magnetic hf loops use such caps, but maybe its because the feed system is NOT symetrical in this case.

Hints anyone ?
Thank you.
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