[TowerTalk] More Radials = Higher SWR???

[Jim Brown]

Hi Dennis,

Study these slides for talks I've done at Pacificon, Visalia, and to 
several local clubs. It's all about antennas, radials, and other 
counterpoises for 160M antennas.

http://k9yc.com/160MPacificon.pdf

A couple of points not made are that: 1) loss in coax is VERY low on 
160M unless the run is VERY long, 2) 2:1 is pretty low SWR, 3) unless 
the SWR is very high and the run is very long, it matters most if the 
transmitter (or amp) is not happy enough to put power into the feedline, 
and 4) SWR is NOT a measure of antenna performance, it is a measure of 
how close the antenna's feedpoint impedance is to the Zo of the feedline.

As an example, I'm using an 80M dipole fed with about 170 ft of RG11 on 
60M, where the indicated VSWR in the shack is about 5:1. Calculations 
say that I'm losing about 1.5 dB in the feedline, so I've got to put 
150W into the feedline to radiate 100W (legal limit on 60M in the US is 
100W ERP). Operating legal limit FT8, I've confirmed 62 countries, and 
most nights can work EU from my QTH near San Francisco.

73, Jim K9YC

On 2/5/2023 3:34 PM, Test wrote:
> I recently erected  my first Vertical (Hy-Gain AV-18HT) antenna and the more
> I try improving it, the more confused I become.
> I added the Hy-Gain MK-160A kit that converts the Vertical to an "L" antenna
> on 160M. For the first time in 50 years of Ham Radio, I was able to work EU
> stations on 160M. WOW!!!!
> I decided to start "Improving" and added my first 4 radials. There's a
> rumor: "You gain and extra 6db of signal if you install antennas in the
> middle of winter in a blizzard." NOT TRUE!!!! The SWR went up a little
> higher, but still workable so I added 4 more.  Now the SWR is over 2:1 on
> all of 160M and is not usable for transmitting.  I disconnected the last 4
> radials from the ground plate but left them in place and now the SWR is back
> to 1.6.
> Grounding Issues? Maybe?
> The ground here is very poor with MANY rocks and solid basalt 18 inch down.
> 8ft ground rods are not practical.  Instead I have installed three 20ft
> galvanized 1 1/2 inch pipe buried as deep as possible in 3 directions from
> the base of the Vertical.  Also I have 500 ft #2 solid tinned ground wire
> bonding all antennas, towers, Vertical, Power entrance point and all devices
> in shack.  I'm located on an 800 ft cliff above Lake Coeur d' Alene in North
> Idaho and we get lots of lightning strikes but that's another story...
> All radials are evenly spaced and 65ft long.
> I'm not sure if I can included attachments of the comparison SWR Graphs so
> I'll also describe the comparisons:
> The colors refer to the attachment if present. The shift in resonates is
> explainable: The antenna wire was slightly lengthened.
> Below are the minimum SWR on 160M taken at the base of the Vertical..  All
> other bands were just slightly affected .
> No Radials= 1.2 SWR (Fuchsia)
> 4 Radials = 1.6 SWR (Red)