Stan,
that is correct, the smaller diameter vertical wire with top loading will
appear electrically longer.
I would model this over Perfect GND rather than Mininec GND. It is good that
you have so many radials. The DE input R drops to 17 ohms and GND loss
becomes that much more important.
Dave WX7G
On Mon, Nov 23, 2009 at 1:01 PM, Stan Stockton <stan@aqity.org> wrote:
> I have a shunt fed tower which is 70 feet tall. It is 45G and has a 6L 20
> on top with a 65 foot boom. It also has a 5L 15M yagi with something like a
> 34 foot boom on the side at about 35 feet.
>
> For the purpose of modeling the antenna with a reflector 100 feet behind
> it, I just put the DE in as a 18 inch diameter, 124 foot tall vertical. The
> actual reflector I have up is a T shaped element that is 100 feet vertical
> and 36 feet on top (18 feet either side of the center of the vertical part.
> This element is #18 copperweld. I have it shown over Real/Mininec ground
> and it shows 5.37 dBi at 1.825. The driven element and reflector have a
> decent ground system tied together in the center with a bus wire - something
> like 100 radials under each.
>
> Am I missing something in the way I am modeling it or should I expect to
> see the results shown by the computer. I am suspicious of the model since I
> can change the vertical portion of the reflector to #10 wire instead of #18
> wire and the max gain moves up about 50 khz. I would have thought it would
> have moved it down some?
>
> I put the reflector back up over the weekend and am going to re-do the
> shunt feed on the tower but wanted to make that reflector element whatever
> length should be best first.
>
> If anyone out there knows how to model this thing properly, I would
> appreciate some help.
>
> Thanks...Stan, K5GO
>
> _______________________________________________
> 160 meters is a serious band, it should be treated with respect. - TF4M
>
_______________________________________________
160 meters is a serious band, it should be treated with respect. - TF4M
|