GETTING ON THE LOW BANDS
A Limited Space Antenna system
 for 160, 80 and 40 meters
By Sean, 2E0BAX

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I have now been licensed for four years and during this time I have enjoyed many aspects of the hobby, which ranges from operating on many different bands and modes including SSTV and Satellites.

As those sunspots kept getting lower in numbers and the higher HF bands were opening less and less I found myself looking more at 40m, 80m and 160m or top band as its known. So I put up an inverted V for 40m and this was a squeeze where I live but it was resonant and works very well with a feed point at 22ft above ground.
See photos below.

Thats the 40 meter inverted V above and the feed point at 22 ft above ground in the photo. Each leg is a 1/4 wave and follows the pitch of the roof about 1ft above the tiles.


The style of house I live in is a Dormer and the gutters are about 7ft above the ground. This is where the legs do a 90-degree bend and are tied to the gutter for about the ten feet or so that remains. This works a treat, has a low SWR and is fairly stealthy. You have to look for it or you would probably not know it was there. As soon as I put it up there was no activity on 40m! Typical, so went onto 20m, tuned it up with an ATU and straight away worked a station in Kuwait! Now its cut for 20m, is fed with coax so theres going to be losses there and who knows how much of my 50w was being radiated?

That's 40m taken care of with a resonant antenna that works very well so where do I put a half wave dipole for 80m? I can only just get a 40m dipole up and now realizing how good resonant antennas are over random / long wires, there is no going back.
 
On the subject of random and long wires, I have used both, but more along the lines of random here at home. Dont get me wrong, they work and they get you on the air but as I have found, they can come with a cost. First thing was RF all over the place namely in the shack with chatting relays and the PSU tripping out making any thing above 17m a no no.

Secondly, TVI to the neighbors on 80 and 160m.

Doublets were never going to fit that would get me on 80m so it was back to the drawing board and a look at what was being used by other Hams in such a position.
I did'nt fancy using loading coils or shortened commercially made antennas besides wheres the feeling of accomplishing something unless you have had some real input?

In one of many experiments later I decided to lay a piece of wire mesh on the lawn and pinned it down with some bike spokes bent like tent pegs. These were very kindly donated by M3PZO. The mesh is about 6ft long and 18 inches wide. I then cut a length of wire for 20m and sloped it to the low gutter, tied it off and checked SWR. It was below 2:1 without any cutting, so I thought I would try it with 50w. I worked all over Europe with ease and to my surprise this antenna fed against the ground worked. I thought you needed a high feed point or at least get it as high as possible? Not if your using the earth as half the antenna which in its self has just halved the size of a half wave dipole and seems to work well without using the ATU therefore reducing losses in the ATU and the coax feeder as it has something around 50 ohms at the feed point.

So there you have some "history" behind my thoughts for getting on 160 and 80 with my limited space.......All of the above experimentation led up to where I really wanted to operate more....the 160 and 80 meter bands!

Now on to experimentation with the 160 and 80 meter bands.......
This is how I did it in the "schematic" below:

Here is a drawing above showing the 80/160m antenna. I cut the 80m leg at 67ft and trimmed for best SWR at 3.5mhz (UK bottom part of 80m). Due to the narrow bandwidth on a wire antenna on 80m you will need to use an ATU. The feed point is at ground level and the radiating wire goes up over the house and into a top room window where I have a crocodile clip (acting as a switch), to attach the 160m section.

The 160m leg is another 63ft and has a loading coil 4ft long with about 40ft of wire space wound on it to reduce the length as I was pushing getting this thing on my small footprint of land. The remaining length, about 10 feet, goes up to the ridge of the roof where the 40m inverted V is mounted.

Here is the earth matt above in the photo ,about 1 1/2  X 6 feet, and you may need to do more than this depending on where you live and your ground situtation. The feed point is on the left lower corner out of the picture.....I'm lucky, I live on very wet ground. It's a peat bog and in fact my house is on a concrete raft and known as a floater!
Bury wire if you need to and check out your ground conditions. Having that other half of the antenna "in the ground" is a very important part of making this work well!
You may need several earth rods several feet long. Experimentation is the best!



Inside the window, I am on 80m with the crocodile clip not connected.
You might call this a poor man's antenna switch...but it works great!

With the clip lead coming from the 80 meter end and connected to the 160 meter section in the photo above, now I am resonant on 160m with a loading coil that I couldn't avoid.
The clip connects the 80 meter end to the 160m section with the coil in line up on the roof. It works!....... and better than I thought it would!

The loading coil is pictured above up on the roof.
 
Final lengths:
The 80m length is 67ft.......
The 160m length (physical length) 90 feet.

It's construction consists of about 40 feet of wire wrapped around the 4 foot form with around 63 feet total of wire used in the complete 160 meter addition to the antenna.  When you add the 80 meter length to this, you get about 130 feet total wire used with the 80 and 160 section tied together.
Total length is 130ft of wire for 160m reduced to 90ft due the loading coil.


Again I went for resonance on the lowest part of the band. This will take some experimentation with the placement of the coil and the total length of the wire at your location. You need to experiment here as the SWR can change a lot with the surroundings.
Using this antenna I have worked all over the UK on top band with as little as 20w making me one happy chap! So if you need a restricted space antenna for getting on the low bands...give this method a try and with some experimentation....
See you on 80 and 160....73 Sean! 2E0BAX s.amesbury@ntlworld.com


Handy Calculator for determining lengths:

http://www.csgnetwork.com/antennaevcalc.html


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