Dennis,
Once you figure out what your impedance converges to as you add more
radials, you might be able to bring the VSWR back down to something more
acceptable with an Unun transformer. I have a 55ft top-loaded vertical
for 160 meters. The feedpoint impedance with a dense radial field is
about 12 ohms (VSWR > 4:1). With a 4:1 Unun transformer, the VSWR
improves to 1.1:1 at around 1830 KHz. The 2:1 VSWR bandwidth is about
~50 KHz. I got the unit I have from Balun Designs.
73, Mike W4EF...............
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)
8 radials = 2.2 SWR Green)
Any comments would be greatly appreciated!
73 es gud DX
Dennis - K7OGW
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