Im looking into building an 11 meter ddrr antenna for my mobile. I curently have a 102 inch whip that works great for local transmissions. The ddrr loks like a simple and cheap build. However, I have had someone suggest a vacume veriable capacitor for tuning the antenna. Is this necessary? I work in the hvac industry and work with mf caps everyday. I am dumb about pf veriable caps. What pf value should i need. Is kv value related to voltage? More watts being pushed higher kv value needed?
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Veriable capacitor for DDRR 11 METER ANTENNA
- Thread starter Jlwhitt77
- Start date
Nothing simple nor cheap about it. Expensive to build; the vacuum cap isn't cheap. Trying to tune the antenna while driving should also be fun. Or whacking the antenna even slightly will put a huge kebash on the whole project. Think you are better off with that 1/4w whip - by far. JMHO . . .
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Actually, The ddrr antenna can be made with materials that I have at my disposal. I figure 3/4 of 7/8 inch soft copper tubing should resonate quite well. The antenna will only be 4 inches above the roof of my truck. That is the height it is designed to operate above ground plane. It will be protected fairly well by the luggage rack on top of the suburban. I could even house it in some way or another. Yeah, its that variable capacitor part that I'm not sure about. If I can use an open air variable, they are reasonably affordable and would make this project all the worth while. Gear that cap up with a 12v slow rpm reversible motor and BAM I can now tune with a flick of a switch.
Knock yourself out, man.
Still think it isn't practical; you asked . . .
Still think it isn't practical; you asked . . .
I understand a vacuum cap is very expensive. Is it necessary? Will an open air cap function in the same way?
Forget the vacuum variable. After a few potholes you will smash the capacitor. Even the constant vibrations from daily driving will eventually damage it. They are electrically VERY rugged but mechanically weak. Your best bet is to determine the value of capacitance needed and then substitute a fixed value. that solves any instability issues and creates a solid electrical connection. You won't really need to tune the antenna during normal use.