20M vertical

After deciding that my doublet works better than the multi-band vertical that I built from a 10M fishing pole, I decided that I wanted to try a mono band vertical.

20M seemed the obvious choice as I could use the 10M pole to create a 1/4 vertical with radials.

Here is what I have:

10M fibreglass fishing pole
Lots of Racal antenna wire
some lengths of rg58 coax
Insulation tape
BNC chassis socket
Some thin cord/rope

First I worked out a 1/4 wavelength of 14.125Mhz (centre of the 20M band) using this formula:

234/F MHz = 1/4 wave (Feet)

That gave me a length of 16’6″ so I cut five lengths of wire to that length. One wire is for the main vertical element, the other four are for the ground radials.

Next to construct was the ugly balun. The ugly balun is a simple choke made from a coil of coax. The inductance of the choke isolates the antenna from the remainder of the feed line and prevents current from flowing back down the outer sheild og the coax. For more info, check out this website.

We need 8 turns of rg58 round a 96mm former to create a ugly balun suitable for 20M. I used an old coffee tin to wind mine. After you have wound it, wrap it in insulation tape to keep it in shape.

Next, I attached a BNC socket to the end of the coax coming from the ugly balun. I use BNC’s on all of my portable antennas so you can put any plug you like on.

The other end of the coax is cut close to the ugly balun and the braid is separated from the centre conductor. Solder one of the wires that was cut earlier to the centre conductor and the other four to the outer braid. Wrap in insulation tape.

Now you should have something that looks like this..

Use some insulation tape to attach it to the fishing pole starting from the top of the pole with the end of the main element.

Once you have the fishing pole up, put each radial out at about a 45 degree angle from the pole. Space the radials evenly. I used some thin rope attached to the end of my radials and some small tent pegs pushed into the ground.

You may need to put it up/down a few times whilst you tune the antenna. I had to cut around 6″ off of mine. Take your time and make sure you don’t cut too much off. My one resonates at 14.125Mhz and is a 1:1 match. It never rises to more than 1.2:1 across the entire 20M band.

The results?

I used WSPR to test out the antenna. First I used my trusty doublet on 20M with 10W of output:

Next, the vertical:

I think its plain to see which one is working better for me!

I am very impressed with the antenna and will be going /P down the beach with it tomorrow so lets see how well it performs.

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