Topband: Cage wire performance

[Dave Cuthbert]

Kenny, your model might have a problem with the acute antenna between the
two vertical wires. I ran EZNEC simulations to test this and compare
against a single vertical wire T reference antenna. Your antenna shows
similar bandwidth, but a different input resistance.

*Antenna 1 *reference antenna
75' vertical wire
from there extend two horizontal 35'wire
SWR bandwidth normalized to the antenna input resistance of *23 ohms*
*SWR bandwidth is 118kHz*

*Antenna 2 *your antenna
perfect GND, #12 bare wire, current segments are 1'
1' vertical wire from GND
from that wire two wires extend to 75' separated by 4' at the top
At 75' the two wires are joined
>From each 75' wire extends a 48' wire
SWR bandwidth normalized to the antenna input resistance of *16 ohms*
*2:1 SWR bandwidth is 100kHz*

*Antenna 3 *your antenna modified to conform to the NEC included angle rule
perfect GND, #12 bare wire
1' vertical wire from GND
from that, 2' horizontal wires extending opposite one another
two wires extend from the ends of those two wires to 75'
at 75' the two wires are joined
from each 75' wire extends a 52' horizontal wire
SWR bandwidth normalized to the antenna input resistance of *25 ohms*
*SWR bandwidth is 106kHz*

*Antenna 4* single vertical wire with a horizontal flat top wires
perfect GND, #12 bare wire
75' vertical wire from GND
from that, 2' horizontal wires extending opposite one another
two wires extend horizontally from the ends of each of those two wires to
22'
SWR bandwidth normalized to the antenna input resistance of *23 ohms*
*SWR bandwidth is 72kHz*

   Dave KH6AQ


On Mon, Jan 4, 2021 at 5:07 AM Kenny Silverman <kenny.k2kw at gmail.com> wrote:

> Hello and HNY!
>
> I will be converting a wire inverted-L to a T top loading on a 75’ tall
> wire hung from a tree. To improve the bandwidth, I was wondering about
> going to a 2-wire “cage” for the vertical section. I’m actually modeling a
> skinny triangle where the wires connect at a point on the top, but with a 4
> foot spread of the wires near the ground. This adds about 15-20 kc to the
> 2:1 bandwidth per the model.
>
> Will a 2-wire section like this always behave as a wide/fat conductor or
> do I have to worry about voltage/current in Each wire?
>
> Regards , Kenny K2KW
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