[Elecraft] Random wires

[dave]

OOPs! Left off part of that vertical that is half of a folded dipole:

In the EZNEC model, those two vertical 1/4 wl elements must be shorted 
at the top with a single segment wire, as well as tied to MININEC 
ground at the bottom.

73 de dave
ab9ca/4



On 10/1/13 7:38 PM, Jim Brown wrote:
> On 10/1/2013 3:42 PM, Fred Jensen wrote:
>> Isn't this why AM broadcast stations, particularly 50KW
>> clear-channel stations, employ base-fed half-wave verticals?
>
> No, that's not the reason. The actual reason is that the vertical
> radiation pattern is better than a shorter antenna.
>
>> They still use radial fields too I think.
>
> Yes. A radial field under a half wave antenna reduces ground losses
> (by a dB or two, depending on how bad the ground is), whether the
> antenna is fed against it or not. But 180 degrees is not the only
> popular height for these clear channel stations -- if you peruse the
> FCC database, you'll see many with vertical heights ranging from 180
> to 225 electrical degrees. Varying the height shifts the balance
> between low angle radiation (for ground wave and long skip) and higher
> angle (for medium distances. Making the radiator a bit taller than 180
> degrees also lowers the Z at the feedpoint, making it easier to feed.
>
> Dave is right on -- most of those posting have confused feedpoint Z
> with radiation resistance. There's a nice graph in the ARRL Antenna
> Book showing radiation resistance of a vertical as a function of height.
>
> 73, Jim K9YC
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