Another thing that the horizontal of an inverted L does for you on 160 is
to give you a penalty-free loading device, so that the ENTIRE extent of the
vertical wire can be seriously used for radiation.
There is a very good, if difficult to prove, case to be made that the
vertical current up near the bend is far more useful in ordinary tree and
building cluttered circumstances. The current near the ground creates low
angle radiation that has to contend with the maximum of clutter-related
dielectric loss in buildings and trees to get in the clear. The same
current near the top only has to clear the top of trees.
If you are in Mr. Donovan's fortunate category and have what amounts to a
vast cleared meadow for an antenna farm, then that issue does not apply to
you, but for every one of him, there are 5,000 hams with small lots FULL of
aforesaid dielectric clutter that sucks up RF launched from near the ground.
A straight vertical wastes the top of the vertical run for launching
radiated signal because the current drops to nothing as you go high. The
horizontal fixes that. Even if you have a 125 foot vertical support
available to you, I still advise an 87 foot horizontal. Yes, this now
presents a miscellaneous feed impedance, and yes, it isn't resonant, and
yes you will have to do some muckety-muck to convert that to 50 ohms
resistive. But there is now serious vertically polarized energy being
launched up high and there is almost no clutter to get over for low angles.
The question is, do you want easy, or do you want killer. Is your goal a
nice, satisfying 1:1 on the SWR meter with no network to get it, or is it
RBN numbers at the far end?
Some say that the horizontal's radiation takes away from the low angle
radiation in the pattern. Really not. Start with a model of a vertical over
bad dirt (what most people have). Gradually add more and more horizontal to
successive models until you get a horizontal of 87 feet. You will find that
the low angle of the pattern changed very little, while the doughnut hole
gets filled in to create a hemispheric pattern with no nulls in it.
Some think that the fill-in energy was taken away from the vertical
radiation. Not true. The high angle seems to get its energy mostly by
reducing ground loss. And remember that the NEC model itself is working on
a W3LPL vast cleared meadow scenario, you can't add in dielectric loss from
trees and buildings to the model. It hard codes assumptions, the best from
your radial field, full size, dense, uniform all around. The model terribly
underestimates loss of ugly radials in ugly dirt. In the more normal ugly
dirt circumstances, RF current up and away from dirt improves things.
If you then put the L over an FCP, to get the feedpoint itself away from
lossy dirt, you get the best of both worlds. Minimize loss near/at the
ground, fill out the vertical wire with significant current all the way,
73, Guy K2AV
On Wed, Nov 30, 2016 at 8:16 AM, <donovanf@starpower.net> wrote:
> Hi Mike,
>
>
> An inverted-L with 50-60 feet vertical is a far superior choice than
> a bottom loaded vertical. Its much more efficient, its bandwidth
> is much broader and you don't have to deal with the very high
> voltages at the base of the loaded vertical, especially if you're
> running high power.
>
>
> 73
> Frank
> W3LPL
>
>
>
> ----- Original Message -----
>
> From: "Don Kirk" <wd8dsb@gmail.com>
> To: "W0MU Mike Fatchett" <w0mu@w0mu.com>
> Cc: "topband" <topband@contesting.com>
> Sent: Wednesday, November 30, 2016 12:32:26 PM
> Subject: Re: Topband: 160 vertical/L
>
> HI Mike,
>
> I use a 68 foot based loaded vertical on 160 meters with 55 short buried
> ground radials (2500 feet of ground radials). I only run 100 watts and
> located near Indianapolis. I would prefer an Inverted-L over the base
> loaded vertical on 160 meters (the L would be much more efficient), but
> having said that I did acquire my 160 meter DXCC last year (all CW) and
> most of the contacts were during years when 160 meters was in very poor
> condition.
> Note: I do use small pennant antennas for RX on 160 meters.
>
> For starters it sure would be easy to temporarily install a base loading
> coil to test out your full size 80 meter vertical on 160 meters versus your
> 33 foot vertical. You can use part of the loading coil you install on the
> full size 80 meter vertical with a fixed high voltage silver mica cap to
> form a simple L network (that's what I do and it works great). This would
> allow you to easily compare your two TX antennas.
> Note: neither end of my base loading coil is connected to ground (my base
> loading coil is between the bottom of my 68 foot vertical and the center
> conductor of my feedline. I use an MFJ 404-0669 air wound coil as my
> loading coil / L network.
>
> But if you can install an Inverted-L easily, than I would skip what I have
> said above and just install the Inverted-L.
>
> Don (wd8dsb)
>
> On Wed, Nov 30, 2016 at 1:33 AM, W0MU Mike Fatchett <w0mu@w0mu.com> wrote:
>
> > I have a full sized 80m vertical and a Top loaded Cushcraft 33ft vertical
> > for 160. The Cushcraft gets out but not great.
> >
> > I was thinking about using an inverted L over the radial field that I use
> > for the 160. It is 30ish radials of various lengths or I have seen where
> > people have loaded the 80m vertical on 160. I think I recall people are
> > not overly excited about bottom loading the 80. The 80 is unguyed so the
> > top cannot support anything.
> >
> > I can get the vertical part of the L up 50-60 feet.
> >
> > Any feelings one way or another? I can make a switching system for the 80
> > vert if people think this is a reasonable transmitting solution. I have a
> > rcv array, so I am hoping to improve my xmit signal.
> >
> > W0MU
> >
> > _________________
> > Topband Reflector Archives - http://www.contesting.com/_topband
> >
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|