10m Bazooka

I am working on some new ideas for building the bazooka antenna.  This one is built with cheap carol RG-6.  This coax has a single aluminum shield without the waterproofing glue so it is easier to work with than the quad shield stuff.  I purchased a 250' spool at Menard's for $30.

I like the conduit bodies for the center but the weak link is the shorting points on each leg.   I am using epoxy and heat shrink on this antenna and yet I think it may not be enough.  If this joint fails the thought occurred to me to use a piece of PVC pipe over the shorting point and fill it with epoxy.  The down fall of this would be the added cost in materials and more epoxy.

This is the center made from a conduit body with a chassis connector installed and a stainless eye bolt, washers, and nuts for supporting the antenna.  The RG-6 has an aluminum shield so I have used crimp eyelets to make the connections to the coaxial connector.  The eyelet going to the center is soldered in place.

Here I have the body filled with 3 oz of 5 minute epoxy, this strengthens the antenna and adds weather resistance.

Here I have one end of the coax stripped back ready for the shield to be twisted around the center conductor and crimped on.

I used a piece of masking tape to mark where the end of the heat shrink tubing needed to be.

I purchased a smaller tube of epoxy with the mixing tip so I could "inject" epoxy under the heat shrink and around the crimp connector that is creating the shorting point.

This is the above connection after "injecting" the epoxy and shrinking the tubing.

 

This is the center after the epoxy is set and a coat of paint applied.

I wrap the connector with masking tape to keep the paint off the threads.

 

I put this antenna up on my 21 foot telephone pole to test it and it has 1.5:1 SWR or lower across the entire band.  The shorting points seem to be solid. (I put plenty of tension on it with the ropes on the ends.)  Although the joints seemed strong enough, I am going to use a sleeve and fill that with epoxy to seal and strengthen the next one I build, most likely for 40m or 20m.

As a side note, the 75m bazooka made with RG-213 is still going strong!

Double Bazooka

I have been looking at trying some different antennae. Field Day is coming up and I am working on some double bazooka antenna builds. This antenna has good bandwidth and is rather simple to build. Some designs claim coverage of the entire voice portion of a band without a tuner.

I have RG-6 to build them from and purchased some PVC conduit T enclosures that have the open panel on one side. I think this will allow me to put the SO-329 connector on them and solder inside the box. I am hoping it will allow me to solder inside and seal the feed point.

I cut down one of the outlets to be flush with the enclosure and mounted the SO-239 on it. I have PVC plugs with holes in them to pass the RG-6 through.

Now the math!

460/f-MHz=overall length of the antenna
325/f-MHz=length of 1/4wave shorted stub in center

What does all that mean? Well, the bazooka can be make in different ways. The one thing that stays constant is the coaxial 1/4 wave stub in the middle. I have seen the ends made of 450 ohm ladder line, 300 line, and good old wire like a dipole. I will be using one continuous piece of RG-6 from one end to the other with the center and outer shield shorted at the 1/4 wave point. Just remember to figure an electrical quarter wave using the velocity factor of the line used. The quarter wave shorted stub is where most of the broad banding of this antenna comes from. The use of balanced lines on the ends may add some broadening by changing the length to diameter ratio. The simple wire would likely not add much if any broadening.

The jacket and shield only are stripped back to allow connection to the feed. The center conductor and shield are shorted at the 1/4 point to create the broadband stub. The center conductor is one piece from one end to the other, do not cut it. The total length is found from the formula previously mentioned.


THIS IS A WORK IN PROGRESS.
PHOTOGRAPHS AND MORE INFO TO COME!