[TowerTalk] Modeling Rohn 25G in K6STI's AO

[Michael Tope]

Mark,

Another possibility is to consider K9YC's advice by making a "fan 
vertical". It's the same idea as a fan dipole, except instead of putting 
multiple dipoles on a common feed, you put multiple monopoles on a 
common feed. I do a variation of this with my 55ft tall 160 meter 
top-loaded vertical. I have a piece of aluminum angle stock U-bolted to 
the tip of the 160 meter radiator so that it sticks out horizontally. I 
don't remember the exact length but it is something on the order of 18 
to 24". There is a pulley on the end of this horizontal piece. I use the 
pulley to haul up 80 and 40 meter wire radiators. The 40 meter vertical 
is separated from the 80 meter wire by ceramic ladder line insulators. A 
short section of the 80 meter vertical slopes down from the pulley to 
make up the difference between a 1/4 wavelength on 80 meters and the 
55ft height on the 160 meter vertical so technically it is an inverted-L.

In my case, I don't have a true "fan vertical" because the 160 meter 
vertical gets wonky when you try to feed power into on 80 meters even 
with the 80 meter vertical in parallel (it caught on fire when I first 
tried it). To get around this I use an Ameritron RCS-4 coax switch at 
the base of the vertical to switch between the 160 meter portion and the 
80/40 meter portion (the 80 meter and 40 meter vertical radiators are 
tied together at the base).

The nice thing about the "fan vertical" approach is that the three 
radiators share a common radial system, so I didn't have to set about 
paving an additional area with copper to get verticals going 80 and 40.

73, Mike W4EF.........

On 10/25/2021 7:33 AM, Mark - N5OT wrote:
> Gawd I got so educated over the weekend.  That was great.
>
> I put up 50 feet of tower, a 12 foot mast, and two 70' long top load 
> wires.  Tuned out the SWR at the shack with a matching network.  
> Stations heard me well, I thought.  Worked Great Britain from 
> Oklahoma, etc.  More data for the cruncher.
>
> I still think traps are elegant, but the most practical solution at 
> N5OT is to keep it simple and put up a different vertical for 80 
> meters in another part of the yard.
>
> Thanks everybody for all the great comments.
>
> 73 - Mark N5OT
>
>
> On 10/24/2021 1:50 PM, Dan Maguire wrote:
>> Hi Mark,
>>
>> Those models are some of the most complex I've ever created. I'm not 
>> sure I could do it again if my life depended on it!
>>
>> Dan
>> On Sunday, October 24, 2021, 04:38:31 AM PDT, Mark - N5OT 
>> <r-emails at n5ot.com> wrote:
>>
>>
>> Thanks, Dan.  I got buried in your content for about an hour and it 
>> was excellent.
>>
>> Mark
>>
>> On 10/23/2021 9:38 PM, Dan Maguire wrote:
>>> Jim Brown wrote:
>>>>>> I've seen a simple equation for modeling a straight triangular 
>>>>>> tower in NEC. As I recall, the diameter worked out to be around 
>>>>>> 0.65 the width of a side. This would account for modeling it as a 
>>>>>> radiator.
>>> The image just below "Wire Geometry" on 
>>> pagehttps://ac6la.com/aecollection8.html 
>>> <https://ac6la.com/aecollection8.html>shows the equivalent diameter 
>>> for Rohn 25G according to:a) Section 9.1 of Leeson's "Physical 
>>> Design of Yagi Antennas"   EquivDia = SQRT(Area / PI) + Perimeter / 
>>> (2*PI) = 9.55 inchesb) Wikipedia 
>>> pagehttps://en.wikipedia.org/wiki/Antenna_equivalent_radius 
>>> <https://en.wikipedia.org/wiki/Antenna_equivalent_radius> EquivDia = 
>>> 2 * (LegDia/2 * FaceWidth^2)^(1/3) = 8.58 inchesI'm afraid I don't 
>>> know which is "more correct".Dan, 
>>> AC6LA______________________________________________________________________________________________TowerTalk 
>>> mailing listTowerTalk at contesting.com 
>>> <mailto:TowerTalk at contesting.com>http://lists.contesting.com/mailman/listinfo/towertalk 
>>> <http://lists.contesting.com/mailman/listinfo/towertalk>
>>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk