Jim,
I changed the subject as I hadn't intended to hijack the previous thread.
I think I have read everything you've written. Have that article right here on
my hard drive in my antenna folder along with numerous others I've gotten off
your site. Thanks for sharing. Yes, I'm aware of all the points you just made.
I'll comment on them below.
Here's what I have done and observed.
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. 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 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 ended up modifying his concept a bit after some testing and to ensure that
the effects of the skin depth he details were overcome on the higher
frequencies by getting more copper closer to the surface. Since his
configuration was intended for use with an antenna mounted on a reef perhaps
with tidal effects in play and my needs are different I decided to explore a
different configuration.
After testing his deeper circular configuration I created a floating ground
that seems to work better in my situation. It consists of two 10', 3/4" PVC
pipes with the ends capped to create two skinny floats. To each pipe is
attached a 14' length of 2" wide solid copper strap. The strap is secured to
the pipes using plastic wire ties. One end of each strap has been prepared so
they can be bolted together at the feed-point. The two assemblies are secured
alongside the boat in a straight line with lightweight tethers. In other words,
it's like a wide floating radial fed in the center. The feed-points of all the
verticals I tested, and now use, are literally within a foot of the water's
surface. The feed-point consists of a Budwig HQ-1 center insulator. Each
version also includes the appropriate choke wound with RG400 coax and wound
exactly as specified in your most recent "Cookbook".
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.
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.
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.
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.
73,
Patrick, W7TMT
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Jim Brown
Sent: Wednesday, March 17, 2021 14:21
To: towertalk@contesting.com
Subject: Re: [TowerTalk] HFT
On 3/17/2021 1:19 PM, W7TMT - Patrick wrote:
> While it would be nice to get a small beam to the top of my mast 45' above
> the saltwater, it isn't practical nor safe. I have to put the antennas up on
> Friday morning and take them down on Monday. It's only due to the kindness of
> my powerboat neighbors I can do that as my antennas occupy their airspace.
Hi Patrick,
I suggest that you study my work on the height of horizontal and vertical
antennas.
http://k9yc.com/AntennaPlanning.pdf
When you're on sea water, you want vertical antennas with a feedpoint close to
the water and a suitable plate that allows connection of the sea water to the
rig as a very low impedance counterpoise. Antennas, horizontal or vertical,
well above water level get very "lobey" in the vertical plane. Propagation of
vertically polarized signals are strongly enhanced by the very low loss first
reflection from the water in the far field, but this effect only works in
directions where the first reflection is over sea water -- in other words, if
you're at the dock without much water between you and land, you don't get that
enhancement in directions that are over land.
73, Jim K9YC
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