[TowerTalk] 80m vertical ideas / questions

[Grant Saviers]

How to make short self supporting decent performance 80 and 160 
verticals is an *interesting* design problem ;) .  My goal is to make 
one for 160m so I can get away from a dense tree area of RF absorbers 
and T supports.

For 80m, a great vertical I had at a prior QTH was 40ft of 3" irrigation 
pipe (guyed) on top of a metal barn roof.  That design had a capacity 
hat of 8 x 6ft 0.375" dia 6061 tubes and a perimeter wire.  I think that 
would scale easily to 40ft of R25 and perhaps a small stub mast to 
support the hat and tune to lower in the band.  40ft of R25 is ok self 
supporting.  It you only have 28ft then add some 2" mast which will have 
lower wind load than R25.

One mistake I made was to use solid Al wire as the perimeter for the 
hat. It fatigued and broke from wind vibration. A high flex copper 
antenna wire some clips that reduce the strain at the hat tips 
connections would be better.  The pipe was base hinged so came down 
easily for fixing.  An R25 version should have a base hinge, but you 
will need a falling derrick rig to raise and lower the assembly based on 
short R25 towers we used on Field Days.

Grant KZ1W

On 12/30/2021 02:00, N1BUG wrote:
> Hi Towertalkers,
> 
> I spent much time this summer rebuilding after storm damage last winter. 
> As part of that I upgraded from inverted V's at 90 and 105 feet for 30m 
> and 40m to an OptiBeam OB1-4030 at 108 feet. I expected improvement but 
> Wow! I wasn't prepared for what I observed! The old antennas on another 
> tower were left up for a few weeks to make comparisons. Unbelievable. I 
> now consider "inverted V" roughly synonymous to "dummy load".
> 
> So... 80m is now my worst performing band, still using an inverted V 
> there. I can work stuff with a shunt fed tower on 160 that I cannot work 
> on 80. I'm thinking a quarter wave vertical for 80 would probably be an 
> improvement and surely no worse. Plus it would eliminate a set of ropes 
> that are somewhat in the way of other projects. But I don't want to have 
> another guyed structure for reasons I won't get into for now.
> 
> I looked at the DX Engineering self supporting 80m verticals. Nice, but 
> they won't fit the budget any time soon.
> 
> So here is a question: Would 30 feet (real height 28 feet) of Rohn 25 be 
> OK freestanding with a 35 foot whip on top? I have a 30 foot whip made 
> from aluminum tubing, tapering from 1.5" down to 1/2". It could be 
> extended to 35 feet with a section of 1.75" OD 0.120 wall tubing I have 
> laying around. I'm confident this whip would be fine, but not sure the 
> Rohn 25 would be OK self supporting with this on top. A 1992 Rohn 
> catalog says 6.4 square feet of antenna with no ice, dropping to 2.5 
> square feet with 1/2" ice. That is for 70 MPH wind and assumes one 5/8" 
> feedline on each tower face. There would be no feedlines and being 
> sheltered by trees this thing would never see 70 MPH winds. 50, maybe. 
> Any experience or wisdom on this?
> 
> My main concern is not that this thing would come crashing down, but 
> that every Rohn 25 tower I have ever taken down that did not have guys 
> on the topmost section had seriously elongated bolt holes. I'm not sure 
> what the deal is there since Rohn seems to be saying they should be OK 
> with small antenna loads.
> 
> Another option might be 28' of tower, air wound loading coil, and 
> somewhat shorter whip.
> 
> Base insulators could be a problem (budget-wise) but I see no reason not 
> to ground and shunt feed a 1/4 wave vertical. I wonder if it might even 
> cover CW and SSB by adjusting the shunt feed capacitor without needing 
> to move the tap point on the vertical? Comments?
> 
> Happy New Year to all and thanks in advance for any comments or 
> suggestions regarding my vertical thoughts.
> 
> 73,
> Paul N1BUG
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