I can see what Jerry K4SAV is talking about. Using a 45 foot vertical
wire and four 65 foot hat wires indicated by EI7BA, resonance is around
2.36 MHz in my EZNEC model. This varies somewhat depending on the
amount of droop of the top wires. The impedance at 1.83 MHz is about 17
- j 282 (SWR=96:1).
Using 93 foot wires (186 feet tip-to-tip) gives resonance at 1.83 MHz
(#14 bare copper wire). The feed impedance (at the bottom) at resonance
is near 25 ohms. (Perhaps John can comment on how he matches the 160m
version.)
BTW, there appears to be an error in the N6LF article
http://rudys.typepad.com/ant/files/antenna_vertical_loaded.pdf , where
he shows the dimension of the hats, L2, as tip-to-tip, but for the model
to work, Rudy's 80m dimension L2 in Table 1 needs to be doubled (i.e.
use the L2 dimension for each of the four hat wires).
With this correction, Rudy's 30 foot high version for 80m can be scaled
to 160m, giving a 55.5 foot vertical section and 168.8 feet tip-to-tip
for the hats, with a feed Z of 29.5 ohms at 1.83 MHz. This is a little
higher than what N6LF shows for the 80m prototype (23.8 ohms), but I
kept the bottom wire at 10 feet high, so the 160m version is closer to
ground (in wavelengths), which tends to increase losses and feed Z.
73, Terry N6RY
On 2009-11-18 2:14 PM, K4SAV wrote:
> John Tait wrote:
>
>> I think you're looking at the 80m antenna, not the 160m version. The cap
>> hats on the 80m are 66ft tip to tip, and the 160m hats are around 130ft
>> . Please read Rudy N6LF's QEX articles on the links provided.. Please
>> also read Tom W8JI's and LB Cebik W4RNL's comments on my page.
>>
>>
> I read all those references before I commented, hoping to find a reason
> for the error. I am looking at the 160 meter version (not the 80 meter
> version), and as you described the top wire is 130 ft tip to tip (two
> wires end to end each 65 ft is the same thing). The bottom wire is also
> 130 ft tip to tip (or two wires end to end each 65 ft), 10 ft above
> ground, and the vertical wire is 45 ft. It appears that EZNEC doesn't
> agree with the description on that page. I can only speculate on the
> reason for the difference.
>
> Jerry, K4SAV
> _______________________________________________
>
>
>
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