Gary, I would recommend a 3 or 4 wire cage feed spaced about 24-36 inches
around the tower as a way to get a better match with a series capacitor or
L network.
Herb, KV4FZ
On Thu, Nov 21, 2019 at 1:41 AM Gary Schafer <garyschafer@largeriver.net>
wrote:
> Trying to make a vertical for 80 meters and 160.
>
> I have an LM354 crank up tower with a full size 40 meter rotatable dipole
> (about 67 feet in length) on it. The tower is about 54 feet tall with a 10
> foot mast on top.
> The dipole is mounted at 2 feet above the tower which puts it at about 56
> feet above ground.
>
> I put a drop down wire on a rod that extends about 2 feet out from the top
> of the tower. The rod is mounted at the top of the tower at 54 feet.
>
> The tower seems to be resonant at around 9.2 MHz with a grid dip meter or
> an
> mfj 259 hooked to the wire and the bottom of the tower.
>
> With a series capacitor on the wire I can get a dip in SWR at around 2.3
> MHz. Going lower or higher in frequency will raise the SWR significantly
> Also tried an omega match but still can't get it to the range wanted.
>
> I want to tune this thing in the 80 meter band first and second on 160.
>
> Can someone model this and tell me if my gamma wire is too long?
>
> I found an article that approximates electrical length of a 54 foot tower
> with a triband antenna to be around 100 feet.
> This calls for a gamma wire length of around 30 feet in the article and a
> series capacitor around 100 pf for 80 meters.
>
> I don't know how much different the top loading of the 67 foot 40 meter
> element will be compared to a triband beam.
>
> With the crank up tower I can put the gamma rod at the top, 54 feet or on
> the middle section at 37 feet or on the bottom section at 20 feet. Those
> are
> the only options.
>
> Any help appreciated.
>
> Thanks
> Gary K4FMX
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|