Jim,
I appreciate the feedback. I am going to test my soil conductivity to see if
I can get a handle on it. You got me thinking, how about if the top and bottom
horizontal
wires were T shaped rather than a single wire bent over ?
Bob
K6UJ
> On Jan 23, 2022, at 11:00 AM, Lux, Jim <jim@luxfamily.com> wrote:
>
> On 1/23/22 9:46 AM, Robert Harmon wrote:
>> No I don't have a 260 foot tower :-) but thinking about this crazy idea.
>>
>> My HDX590 tower is 90 feet fully extended. By attaching to the side of the
>> mast 15 feet up I can have an attachment point at 105 feet.
>> I am envisioning hanging a vertical dipole from the 105 feet point and
>> running the top wire horizontally 82 feet sloping down to a 30 foot mast at
>> the corner
>> of my property. Likewise on the lower end of the dipole 9 feet high and
>> going to the other corner of my property. This woud put the center of the
>> dipole about 57 feet
>> above the ground. I don't know how a dipole will work with the ends bent
>> this way but maybe it would be more efficient than a vertical with a
>> compromise radial field.
>> An option might be to make two big boy loading coils and shorten the dipole.
>> What do you think of this idea ? Am I off my rocker ? hihi
>
>
> You're not off your rocker, but pay attention to the inherent problems with
> vpol being strongly affected by the soil properties in the area -
> particularly for low angles.
>
> What's interesting is that the directivity of a infinitely short dipole is
> 1.5 dBi, and a full size half wave is 2.15 dBi. So a shortened dipole with
> capacity hats, loading coils, or matching network will be pretty much the
> same (within a 1/2 dB) as far as the far field goes for the same center
> height.
>
> Your issues are going to be losses due to the fields interacting with the
> soil AND losses in your matching networks (whether at the feed or loading
> coils, or whatever). The radiation resistance is smaller, so the current in
> the antenna (for the same power) will be higher, so you get more IR losses.
>
> Those can be driven down by using bigger wires, etc.
>
> The other thing that happens is that the impedance will vary more quickly, so
> you might need an adjustable matching network.
>
> You might also look at making the bottom of the dipole a "cone" (even
> shortened), because that improves the matching bandwidth. Cones (and fan
> dipoles) are broader band than single wires.
>
>
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