Topband: Top band dispondant

[Guy Olinger K2AV]

The answer to this one comes in several parts.

Your antenna is composed of a "pole" (the up 40 and out 20) and a
"counter-pole" (your elevated loaded radials).  Power is DRIVEN into
BOTH of these necessarily. Contrary to a dipole (where pole and
counter-pole are identical and opposite, and both intended to
radiate), usually on 160 the counter-pole is designed to accept power
and then give it back dissipating or radiating as little as possible.
The design and efficiency of the pole and counter-pole are separate
issues, and from my reading of your post (however accurate or not)
contain rectifiable problems for either in your case.

If the counterpole (raised radials, buried radials, counterpoise) is
already well designed for very low loss and very low radiation, it
will not figure much into the performance of the pole portion of the
antenna.  Let's first consider the pole by itself.

If the pole is a wire that only goes up 40 and out 20, on 160 the
current will be zero at the end of the out 20 wire, and some current
level related to power at the feed and a pretty low feed resistance at
the feedpoint.  Looking at a graphical representation, current will
nearly linearly reduce in amplitude going from the feed to zero at the
end. With the power related to the square of the current, the first
thirty feet of wire will be responsible for radiating 86% of the
power.

The highest current will be closest to the ground creating the highest
possible ground field losses for that power and length of wire. And
since the highest possible current will be at the feed, therefore the
highest possible current will be going into the counterpole, creating
the highest possible counterpole ground field loss for that power, for
that counterpole design and length of radiator.

In your design the feedpoint is only 40 degrees from the current zero
at the end of the wire. If instead we do something folded-wire at the
end of the out 20 wire to get the feed point at 110 degrees from
end-of-wire, then the current max will be in the middle of your
radiating wire and current almost evenly distributed over the
radiating wire.  This will reduce feedpoint current to 0.59 times
previous value, and multiply true feed R by 2.86.  Given that most ham
radial systems are NOT dense or or not uniform, the effective series
resistance of the radial system is often fairly high compared to
commercial radial systems. The radial system's effective series
resistance is often in the same range as the radiator's radiation
resistance, sometimes greater, and a large portion of drive power is
lost in the ground.  Multiplying the feed R, by moving the current max
off the bottom and up the radiator, lowers the current that has to be
driven into the counterpole, and lowers I^2*R losses in the ground.

The COMBINATION of a 5/16 wave single wire folded counterpoise (FCP)
AND top-loading the vertical can make a very large difference.  Either
one has been known to make a large difference.  And since an FCP is so
much more compact than other counterpole alternatives, that aspect may
allow you to improve your vertical radiator run.

To create a 70 degree top-load, take a 104 foot wire, run it out west
26 feet, then parallel back to the center, then out east 26 feet, then
parallel back to the end insulator at the center. This will look very
much like a 52' folded dipole without a feedline.  You just take the
top of the up 40 out 20 main vertical wire and attach to one side of
the folded dipole feedpoint.  Leave the other side of the folded
dipole feedpoint open and insulated as the end of the overall wire.
The top load folded dipole can have the ends droop down 45 degrees,
like an inverted vee folded dipole, without any ill effects. The
radiation from the top load tends to cancel out.  450 ohm open wire
ladder line would be ideal for this.  Use of the 360-400 ohm PE
sheathed "450" window line (Wireman #554, etc) MAY have some loss
associated with its use.    I have no data on that.  Use of Wireman
#554 with a threaded center third conductor for FCP construction did
prove lossy.  The top load WILL be carrying the same current at the
FCP but will not have the threaded third wire in the center.

FCP construction and material details for the required isolation
transformer may be found at w0uce.net/K2AVantennas.html

People ARE making significant improvements in 160 performance on
building lots once deemed too small for 160, and absolutely too small
for radials.

In general, use of a 70 degree reduced or no radiation top-load will
elevate the current maximum to an optimum height for any vertical size
up to 110 degrees.  It's chief advantages are to 1) reduce ground
field induction losses, and 2) improve low angle skywave radiation.  I
have finally figured out ways to make this visible at least in NEC4
based models.

73, Guy.

On Thu, Feb 2, 2012 at 1:31 AM, kd1ia <kd1ia at cox.net> wrote:
> HI all,  I have had a rocky relationship with TOPBAND that has never really blossomed.  My QTH is small about 1/4 acres.  Only two tree's and NO towers allow.  Now that has not stopped me.  I have WAS on 160m  (took 10+ years)  and a splattering of countries.  But I will go on to my problem.  I am just NOT heard.  I can hear great with my selection of antennas (resonant on 160m I have a inductively loaded INV L vert about 40ft 20ft horiz (home brew by the insane mind that is my own with 4 elevated radials also loaded like the radiating element) A Cushcraft ma160v with about 40 radials on the groud.  A Alpha delta dxa with about 50 radials on the ground. These radials are all random ranging from 1/16 to 1/4 wave. )  The verticals make great contest antenna for stateside as the cushcraft is resonant from about 1.800 to 1.825 and the Inv L flat from 1.820 to about 1.850.
>
> This all aside I can hear like I'm running a receiving loop or even a small beverage (had a nice one at an old qth back in the 90's) but I cant seem to be heard.  I can put 1kw++ into these antennas but still no luck most of the time.  For example I have been calling the HK0NA tonight on 1.833/4 he is s9+ on 1000d and I am not even getting a ??
>
> Other than the WARC band and my eternal quest for a bigger signal on 20/30/40m I am happy with my antennas.  Though I admit I am always experimenting and have a separate operating position just for experiments and the rare guest op.
>
> Well if I'm just crazy then so be it.  I've been banging my head on this problem.
>
> Any suggestions would be welcome. I an willing to direct email larger descriptions and even pictures of what I am working with...
>
> Caveats: I wasn't born yesterday,  But, I do believe in magic. sooo Other than buying out all my neighbors and putting up some big antennas lets try and be constructive.. (that is unless ya wanta give me themoney to buy out my neighbors 8)  )
>
> de John ko1h
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