Only 2 elevated radials instead of 4

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Jason Hsu:
The conventional wisdom is to use 4 equally spaced radials for an elevated vertical antenna.

But studied have shown that an elevated vertical antenna with 2 equally space radials (in other words, 180 degrees apart) provide both efficiency and a radiation pattern within a few tenths of a dB of that of an elevated vertical antenna with 4 equally spaced radials.

So why use those extra two radials when they don't accomplish much?  As necessary as the first two equally-spaced radials are, they provide no net contribution to the radiation pattern.  Since the currents in the radials flow in opposite directions, the radiation fields they create cancel each other out in the far field.

Dan:
Long thread on "Do Radials Radiate?"

http://www.eham.net/forums/Elmers/203128







Claude Stewart:
Supposedly a two radial system was proposed in the early days of police radio, but the customer felt more was better, and leaned toward a four radial design. Since the customer is always right, the four radial system won out.

Another reason for more than two radials is their usefulness as part of the guying system. Again, four guys are better than three, or so believes the customer....

Eric P. Nichols:
It's really just a matter of efficiency.  2 radials can be quite efficient if the antenna is up high enough. K8CH describes such a beastie in the 1991 Antenna book...and a few other years, i presume.

Eric

Charles:
I agree with W5FYI's, F.Y.I.

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