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Author Topic: 40 Meter Antenna for 15 Meters  (Read 26085 times)
KX4OM
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Posts: 367




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« Reply #30 on: December 27, 2015, 05:27:13 PM »

...I've searched and searched and can't find the references to adding the wire.  I can find several references to simply using the 40m antenna for 15 without much explanation.

1.  Is the wire necessary?

2.  If so, what are the details on using the wire?

3.  Are there any drawbacks to doing this?

4.  I'm building a vertical and could simply add another element for 15.

Thanks      Ray

Are you planning on building a 1/4-wave 40 meter vertical using wire? If so, the length of the wire will be somewhere in the 32 to 33 feet range. Now, for the 15 meter addition, you could build a resonant trap for 15 meters, which can be as simple as a coil in parallel with a capacitor. You'd need to do some research on traps. The trap would be positioned approximately 11 feet above the feed point (in other words, about a 1/4-electrical wavelength for 15 meters.)

On 15 meters, only the portion of the antenna up to the bottom of the trap is active. The trap disconnects the rest of the antenna. On 40 meters, the entire length is active, and the entire length will be shorter than the 32 to 33 foot length of a single band 40 meter vertical. In the trapped antenna, the coil in the trap acts as a loading inductor for 40 meters, reducing the electrical 1/4-wave length. A ground-mounted vertical antenna will need radials to reduce the ground loss.

73, Ted, KX4OM
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