How Well Does A Trap Dipole Work

Discussion in 'General Technical Questions and Answers' started by KJ4BIC, Nov 6, 2008.

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  1. W8JI

    W8JI Ham Member QRZ Page

    Which is my point. The little we gain in one or more narrow specific directions or angles always is accompanied by a great deal of loss in other directions, plus the overall radiation efficiency is less with really long wires.


    That is true on a single band or a few bands Cecil. But the point of discussion here is a a 80-10 meter antenna, not a 20 meter only antenna pattern.

    The fact is if we cannot control and plan the pattern to NOT decrease signal level in all the directions we want to work, we are far better of to not have the nulls. A half-wave dipole is very tough to beat as a general all around antenna that cannot be rotated.

    73 Tom
     
  2. W5DXP

    W5DXP Ham Member QRZ Page

    That 20m plot was just one example. I have radiation plots for all the HF bands for my 130 ft dipole. Often, that 130 ft dipole outperforms my 20m rotatable dipole even in the rotatable dipole's favored direction. Just because an antenna has nulls is no reason to dismiss it entirely. After all, an ordinary 1/2WL dipole has nulls. When I was in high school, I had a devil of a time trying to work stations directly north of my N/S 40m 1/2WL dipole.
     
  3. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    Lets take a typical 3 element yagi beamwidth of about 37 degrees. Now, lay two pieces of string out with a 37 degree angle at the apex and measure the distance between them at 1000 feet. Now measure the distance between them at 250 miles, is it the same? No!

    Measure it at 1000 miles and the footprint gets even larger. It's still more concentrated than if the source was radiating equally in all directions, that's why beams work. But just like a flashlight beam the energy spreads out over distance. So it goes with the lobes that you are refering to. They are not finite in their shape and they are far less apparent unless the antenna is at least 1 wavelength above the ground.

    You need to think about how to help new hams get on the air easily instead of trying to discourage them by telling them that a time proven all band flat top won't work when indeed, it is one of the best performing simple wire antennas ever.
     
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