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What's the purpose of the extra set of plates on this Air Var Cap? Johnson 169-25
- Thread starter Naysayer
- Start date
A dual gang air gap variable capacitor, used to see lots of them in old AM tube radios.
You can use one gang separately from the other for different functions.
73
Jeff
You can use one gang separately from the other for different functions.
73
Jeff
It's just 2 more caps? Yet, they are inverse-synched to the primary 2 sections. My small brain couldn't grasp the use of such an piece.
Was considering it to replace my Load cap and remove the extra hardware. (1 I have now is too narrow range) but could not find specs for a Johnson 169-25. Do the Johnson stock numbers translate into the C specs somehow?
Was considering it to replace my Load cap and remove the extra hardware. (1 I have now is too narrow range) but could not find specs for a Johnson 169-25. Do the Johnson stock numbers translate into the C specs somehow?
A great article about that Johnson matchbox explaining those caps.
https://www.qsl.net/w2wdx/articles/a4.html
https://www.qsl.net/w2wdx/articles/a4.html
That's a cool link. Thanks.
It's all about a balanced circuit split either side of ground. The split capacitor tunes each side of the balanced circuit with the center tap grounded.
73
It's all about a balanced circuit split either side of ground. The split capacitor tunes each side of the balanced circuit with the center tap grounded.
73
Same Cap!
"it does serve to improve feed-line balance and reduce the potential for feed-line radiation. Most coax systems are already referenced to ground via chassis ground or shield grounding at the point where the coax enters the shack. It is a design form which is only important in terms of using balanced line; a reference to ground for a normally floating balanced line" There I go. Thank you Sunbulls
"it does serve to improve feed-line balance and reduce the potential for feed-line radiation. Most coax systems are already referenced to ground via chassis ground or shield grounding at the point where the coax enters the shack. It is a design form which is only important in terms of using balanced line; a reference to ground for a normally floating balanced line" There I go. Thank you Sunbulls