[TowerTalk] Sailboat Antennas

[Jim Brown]

Hi Patrick,

On 3/17/2021 5:35 PM, W7TMT - Patrick wrote:

> I've a good amount of seawater on three sides. Nearly six miles of open water to the east, 1 mile to the west, and 1/2 mile to the south. Only a 100 yards or so to the north.
> 
> Yes, studied your model results regarding the change in patterns with elevation and took them into consideration. You state on Page 13 "Lobing begins as the antenna is raised above about λ/2 (33 ft on 20M)."  My 40M dipole is only at about 45' high so it's fits within that guideline. 

When lobing starts is not necessarily the right guideline, especially if 
your interest is DX.  Study Fig 25, noticing that for 40M, radiation 
below about 25 degrees keeps increasing up to about 60 ft. This is for 
average ground.

The 20M antenna is right at 33' high the same as your Figure 31 plot. 
Any lower and it is very close to the upper, mid, and lower shrouds. 
Those being the guy wires on the sides of the mast in case you're not 
familiar with the sailboat rigging terminology. Tried that antenna lower 
but it plays much better higher due to the interaction with the rigging 
wires. The diploes are at the best heights and elevations that the mast 
and rigging configuration allows and in fact I think they fit within 
your recommendations.

Yes, I think you've made great use of your resources.
> .
> Yes, I have a low impedance counterpoise for the verticals. I started out using the circular configuration that Rudy, N6LF describes in his Seawater Grounds article here:
> 
> (http://www.arrl.org/files/file/Antenna%20Book%20Supplemental%20Files/22nd%20Edition/Seawater%20Grounds%20-%20by%20N6LF.pdf)
> 

> I started out assuming all the verticals would be the winners. The results have been band dependent. The verticals win hands down on the lower frequencies but lose to the diploes starting at 40 meters.

That's not surprising, given that you were able to get the 40M antenna 
fairly high.
> 
> My 160 M vertical  is 80' long and inductively loaded below the mid-point. Inductor was wound using W8WWV's techniques out of 1/8" refrigeration tubing. ( http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/HiQCoil.htm ) The coil is not located at the best spot electrically as it is only 25' above the feed-point but that's as high as I can support it given its weight and size. The first 38' of the antenna is supported by two sections of MaxGain pushup mast with an old 25' Steppir beam element tube on top. Only the first section of the MaxGain mast is guyed. The wire comes off the top of the lower mast and goes to a 31' Jackite telescoping pole that is mounted to a carrier that slides on the mainsail track. The wire intersects the fiberglass mast about 6' above the boats aluminum mast.

Based on a lot of good work I've studied on the topic (there was a GREAT 
2-issue piece on the loading of mobile antennas in QEX 5-10 years ago), 
you might want to look into top loading the 160M vertical with multiple 
wires, rigged as close to horizontal (or with as little down-slope as 
practical). The problem with base loading by inductance is that the 
inductor is at current maxima for the antenna, and that's the part of 
the antenna that does the most radiating. Too much down-slope of the 
top-loading wires reduces the effective height and the radiation 
resistance, reducing the efficiency. This could make a difference of 
several dB.

For an extreme and VERY innovative example of end-loading, study the 
first 630m antenna on VK4YB's qrz page. Nieghbor W6GJB built a version 
of this antenna that I tweaked a bit in NEC to fit his real estate. One 
trick was to break the end loading wire into multiple wires that provide 
enough loading and fit his real estate. It's played quite well for Glen 
-- he's worked VK4YB with about 60W. The key to this antenna is to tweak 
the lengths of the feed wire and the loading wire(s) so that current 
maxima occurs in the vertical section.
> 
> This antenna plays very well. With a 100W I've done very well this season on 160M by Pacific Northwest standards. My scores have been near the top and may be winners in several of the events. I'm definitely  NOT a very talented operator so that says a lot about the antenna.
> 
> A straight 1/4 wave wire using the same floating ground and similar dual mast support plays well on 80M but to be honest that band isn't my focus.
> 
> On 40M, a 1/4 wave wire with the same setup, but only the deck mounted mast required for support has been a bit of a disappointment. When compared in contests and casual operating it only rarely beats out the dipole.  Using the JA path as an example the vertical should have an advantage as there is about a mile of saltwater in that direction and the closest sailboat mast is 150 feet away and not even in the direct path. Only rarely does the vertical clearly beat the dipole. They are not infrequently tied but the dipole at 45' high usually wins and of course the receive noise is far lower.
> 
> Did a lot of 20M testing as well. I won't say never, but rarely does the 20M vertical beat the diploe. This happens even if the station is right off the end of the dipole like a W6. Based on the 20M results I didn't test anything on 15 or 10M.
> 
> What's the problem? Besides the fact that there is no way to get the verticals more than 16-18' away from my own vessel's mast, at the dock I'm located in an aluminum forest. I've nothing to the north but the closest sailboat is only 28' away from my mast to the south and there are nine more of them in a row after that. To the east the closest mast is barely 50' away directly off my bow. That row extends 6 boats in one direction and 11 in the other. There's another long row of them 60' beyond that. Not too bad to the west as that's another facility 150' away with not many sailboats at the moment.
> 
> As every article on verticals mentions, nearby vertical conductors mess up the patterns. Both K3LR and W3LPL make mention of interaction issues with towers and other antennas hundreds of feet away. Not saying I can't improve things a bit more but the limitations of the environment are fixed. Getting off the dock and away from the other boats is of course the ideal situation and I do that when I can. Just not always possible especially in the Winter.

All of this agrees with everything I've learned. Rudy has written about 
that too -- a piece maybe 10 years ago about the effect of towers that 
are electrically shorter than a quarter wave.
> 
> So I've found the 160M antenna works really great.  80M nothing to complain about. 40M and above the diploes do better because they are just so much more in the clear. This is true especially to the east with six miles of seawater being the first thing they see.
> 
> Thanks for your suggestions and all the great work you have contributed to our service. I've got a stack of your chokes here and they are the best I've ever tried.

Great to hear it. Ham radio has always been about sharing and helping 
each other. I got lots of help when I was starting out, I continue to 
learn from others, and I try to do my part by sharing what I think I know.

73, Jim K9YC