[600MRG] For discussion: Re: Top loading a vertical on LF/MF

[William E. Isakson]

I  have used both top loaded and mid loaded verticals Neil.  In the case of
the top load the wires did slope back some, but not more than 25% less than
the antenna hieght.   This antenna was about 18 feet tall 1-1/2 inch copper
water pipe and the grounding was  provided by many ground wires, none
exceeding 143 feet in length.   I provided some army surplus fiberglass
poles (actually intended to support camo netting) to support the top load
wires not far from the perimeter.  There were eight or more top load wires
and a perimeter wire.   There was also a tapped coil up top.   I think that
if you are not going to provide poles to support top load wire then the
wire that you use ought not to be more than about 1/4 of the length of the
line, the remainder can be poly cord insulated from the wire. (yes you must
insulate it, the polymer conducts.)
The other antenna was about 36 feet tall and mid loaded with a tapped coil.
 The grounding in this case was fewer radials and several ground rods that
tapped into the high water table.  The location was several blocks from the
san francisco bay mud flats and there was salt intrusion.  The cement slab
floor of the garage often had salt left from evaporating water that
diffused through the unsealed floor.  I tried to get the landlord to seal
it (this was an apartment house, by the way, which is why radials were not
extensive) but that never happened.
Local testing showed that these two antennae were fairly matched for
performance.  There was one incident, though, where reception of my tenth
watt ERP signal was made in Oklahoma from the top loaded version, but there
was no such long distance report associated with the mid loaded vertical.
In general, though, I liked the mid loaded version better from an aesthetic
standpoint.  If you had a radio on in your car and parked in the driveway
just next to the top loaded version, there was interaction between that
antenna and any band listened to in the car that dramatically improved
reception.
I did not try a bottom loaded vertical since that seem intuitively
unreasonable.  With bottom loading you are working with the top portion of
what would be a full sized antenna and it is just a small portion of it
where the current is effectively near zero, but with top loading you are
working with bottom of that same full antenna where the current in maximum.
  In the case of the mid load antenna you get both the top and the bottom
while the rest is in the coil, so all the action comes from the bottom
section while the top half does relatively nothing but be there--you might
as well turn it to the side.....
Bill Isakson
neè  WD2XSH/44, now in Roseburg, outside of transmitting area.

--------


Bill Isakson     AC6QV
Roseburg, Oregon USA
bill.isakson at gmail.com

"assume all else is random fluctuation of coinkidinky"


On Wed, Nov 27, 2013 at 3:18 PM, Neil Klagge <w0yse.7 at gmail.com> wrote:

>  To the 600m gang:
> The reason for initiating this discussion is that, for me and perhaps
> others, it is not feasible or possible to add top loading wires to a 630m
> vertical without sloping the load wires downward a considerable amount.
>
> I know that when an antenna is “folded back on itself” there is
> cancellation of some of the radiation from the antenna. This is certainly
> the case for top loading wires that reach toward the ground down to less
> than half of the height of the vertical section.
>
> The question I find myself asking is this: “Is what I will gain in ERP
> worth the effort it takes to add sloping top wires because of the
> cancellation that will occur.” I wonder if 1 or 2 dB gain is worth it at
> the receiving end.
>
> I would be interested in feedback from those who have any experience with
> both situations: Namely, top loaded verticals and “topless” verticals  ;-)
>
> 73, Neil Klagge, WG2XSV, W0YSE
>
>
> --
> *"I use the original form of social networking, Amateur Radio." *
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