DOUBLE BAZOOKA/COAXIAL DIPOLE ANTENNA

                 -------------------------------------

A typical, dipole antenna has bandwidth of about 50 to 100 KHz.  The

bazooka is  resonant in the center of the band and had an SWR of 2:1 or

less across the entire 80 meter band?

  The "Bazooka" antenna was developed by the staff of M.I.T. for radar

use.  The original "Bazooka" used coaxial cable for the entire radiating

elements. 

 The adaptation used in amateur radio uses coax only for

 the broadbanding portion of the antenna, while the remaining

 portion of the elements are constructed of twinlead or ladder

 line (see attached sketch).  Ladder line is preferable for its

 inherent strength.

   This is a single band antenna.  It will not radiate harmonics

 of your operating frequency.  In addition, there is very little

 feedline radiation, which is great for those who have problems

 with TVI.  Its broadband characteristic makes it ideal for 80

 meters and 10 meters.  

The Bazooka 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.  The outside

 of the coax and the ladder line operate as a half-wave dipole. 

 The inside of the coax elements, which do not radiate, are

 quarter-wave shorted stubs which present a high resistive

 impedance to the feed point at resonance.  Off resonance, the

 stub reactances change in such a way as to cancel the antenna

 reactance, thus increasing the bandwidth of the antenna.

 At the very center of the coax carefully cut away about one inch of the

outer vinyl jacket. 

Then cut the exposed shield 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 ladder line

 wires to the end of the antenna element.  At the other end of the

 ladder line, solder the two wires together. 

 Use a square piece of plastic at the antenna center, drilling a 

small hole on each side of the coax, wrapping a small wire around the 

coax and through the holes and twisting the wire together on the other 

side. A small amount of quick setting epoxy secures the 

coax to the plastic support and prevents the wire from untwisting.  

A coating of silicone rubber or epoxy seals and protects the feed-point

from the weather.  Do the same where the ladder line is soldered to the 

shorted end of the coax.

 Short the center to shield at each end of the coax.

 Short the twin lead at each end and solder the coax/shield juction

 to the coax.

             50 Ohm Coax feedline     

             at least 66 feet long.         

                               shield side         center connection side              

     ___________   ________________|   |________________    ___________ 

    |___________|- [|__________________________________]- [___________]|

       Twin-Lead                    coax                   Twin Lead

                   <---------------L=325/F-------------> 

                                  coax length

    <----------------------------L=460/F------------------------------>

                                total length     

example:                3.888 kc

total length          118.3 feet

coax length            83.6 feet

twin lead length     34.7 feet