*The Bazooka Antenna*
By Katunk

A portable field antenna

 

Sometimes called the double bazooka or a coaxial antenna. I have built several for different frequencies and on the 20 meter one I am always getting good reports from the Canary Islands to Moscow. Mine is oriented North / South and I am really impressed with the performance above 30 feet. Mine hang off of a couple of trees between my front and back yards.

 

The antenna is really easy to make and with enough nylon rope you can set it up anywhere thereís space. You can even set it up as a sloper or inverted V if so desired. I used RG-8X and it hangs nicely with quarter inch rope.

 

With a very little tweaking with a tuner I can work all of the 20 Meter Band. I also have had similar results for one cut for 10 Meters.

 

Nuts and bolts

 

This is a single band antenna that does not radiate harmonics, has very little feedline radiation, (cuts down on TVI). The antenna consists of a half - wavelength of coaxial line with the outer conductor opened at the center and the feedline connected to the open ends. For the ends I use 18 gauge copper wire. At the very center of the coax carefully cut away about one inch of the outer vinyl jacket. Then cut the exposed shield ONLY all the way around at the center of the exposed area. Be careful that you do not cut the dielectric material or the center conductor in the process. Twist the two pieces of exposed shield into small pig-tails. These are the feed-point terminals for the antenna. The center conductor of the feedline is soldered to one and the shield of the feedline to the other. Now solder the center conductor and shield together at each end of the antenna element. Solder the two 18 gauge wires to the end of the antenna element. Loop and solder the ends of the wire. I used these little u type connectors I got from the hardware store for this. It allows you to trim the antenna if needed without the hassle of soldering. Tie some rope to the end and chunk the other end of the rope over something ( the higher the better of course. Do the same thing on the other end and youíre in business. I made a T shaped piece of plastic at the antenna center, drilling a two small holes on each side of the coax, and used tiny tie wraps as strain relief. I used coaxial sealer or some epoxy to keep the water out of the center and the ends of the antenna. The feed line should be the same impedance as the antennas coaxial body and at least 66 feet long.

 

Feed line

 

_________________________| |_____________________________

------------|_________________________________________________________|------

|----------------------------coax section------------------------------------|

|---------------------------------------------overall length------------------------------------|

 

Not the prettiest drawing but you get the idea. The center is the coax, the rg58. Dotted lines on the end represent the 18 gauge wire. I know! If you look on the internet instead of wire they use shorted twinlead. The first one I built used twinlead but it was a pain to work with. This works just as well and is much easier to set up.

 

Now the formulas:

The length of the coaxial section is = 325/F (in kHz)

Overall length is = 460/F (in kHz)

Wire ends = overall length minus coax length divided by 2

 

 

There is lots of info on the internet about these types of antennas. Go to your favorite search engine and type in "bazooka antenna". Since itís a coaxial antenna roll it up and take it with you.

Katunk


All materials at this site not otherwise credited are Copyright (c) 1996-2002 Trip Williams. All rights reserved. May be reproduced for personal use only. Use of any material contained herein is subject to stated terms or written permission.