Bazooka Dipole

bazooka /buzooca/, n. a cylindrical rocket launcher, an individual infantry weapon that fires a rocket…

(Macquarie Dictionary)

As the name suggests, the Double Bazooka dipole antenna is a hard-core DX killer capable of some DX-treme QSO carnage on 27 MHz frequencies!  Not only is this particular type of antenna an attractive option for DXpeditioners working from ham unfriendly locations but its stealth qualities are also appealing to those radio hobbyists who are hamstrung (excuse the pun) by local council antenna restrictions and cannot erect a large antenna array.

First used in military conflicts to assist with stealth communications between army bases, the Double Bazooka antenna is an extremely broad banded half-wave antenna which can operate efficiently across an entire band with little change to the SWR.  This antenna design was first conceived as a radar antenna in the early 1940′s for use by the U.S. Government.  It was later modified for amateur radio use in the 1950′s and in modern times is great for those DXers who suffer from TVI.

Unfortunately, home-brew Double Bazooka antennas rarely survive harsh elements and wind-load stresses as the weak points are typically at the feed point and coax to twin lead connection.  The I.A.C. design, on the other hand, is the culmination of a three year development program, including state of the art materials and encapsulation techniques, to provide the DXer with an antenna that will endure such harsh elements.  Construction methods and components used are of government Mil-Spec quality.  Antenna construction centres around 50 Ohm coax, in combination with 300 Ohm transmission line end sections.  The end result is a centre feed broadband full wave dipole.  Provided for the operator’s 50 Ohm feed line is a SO-239, a silver plated connector having Teflon insulation and a gold plated socket.

The features of the proprietary design anchor the connector in high shear UV resistant moulding. The coax elements are sealed in this moulding, which exhibits high adhesion to the PVC jacket.  Mil-spec heat shrink tubing, with a melting inner liner, is utilised to seal and strain relieve the transition area between the coax and the twin lead.  Heat shrink caps are applied to the outermost ends of the twin lead completing antenna construction.

This unique design eliminates the need for antenna matching baluns and can be fed directly with 50 Ohm coax.  The Double Bazooka is 98% efficient and typically provides S.W.R. readings of less than 2:1 over the entire amateur band.

Since this antenna has no exposed metal wire, static charges can not build up thus reducing noise by 6dB over antennas constructed of exposed wire.

On the ham bands, the Double Bazooka antenna will handle full legal limit power with no effect to performance.  It is recommended to be mounted in an inverted “V” configuration for optimum results, however, the Double Bazooka can be configured horizontally with equally good results!

The 80 Metre Double Bazooka antenna will operate on 80 through 10 metres, including 11metres, with the aid of an antenna tuner.  It can be configured as a phased array with an optional add-on kit with the phased array producing up to 4.5dB forward gain and a front to back ratio of typically 20dB over a single dipole antenna.

The following chart gives overall antenna lengths and recommended height placement above ground for a single Double Bazooka:

Measurements

• Length a to e= 468 into frequency (example 468 divided by 1.900=246.32 ft)
• Length b to d= 325 into frequency (example 325 divided by 1.900=171.05 ft)
• Feed-line 57/ 87/ or 103 feet for optimum performance

Materials Needed

• rg8x (high power), rg58, or rg59
• hot glue and hot glue gun
• solder and soldering iron
• pl 259 connector with proper adapter
• empty plastic frosting container with lid
• small nylon rope
• plastic insulators if you want to get fancy

Getting Started

1. Measure length of dipole section and cut 246 feet 4 inches
2. Find centre exactly mark with electrical tape (point c see diagram)
3. Determine length of point b to d and divide in half 171/2=85 feet 6 inches
4. Start at c and measure 85 feet 6 inches and mark with tape both ways these will be your b and d measurements
5. Cut length of feed-line 103 feet

Antenna Surgery

1. Take an empty frosting container and remove the lid
2. Cut main container up one inch from bottom
3. Drill 3 holes in side to accept rg8x coax at proper entry points
4. Feed dipole section in one hole and out the other and leave point c inside
5. Feed-line should enter through remaining hole
6. Remove 1 inch of vinyl at point c
7. Carefully separate braid into two pieces – do not disturb centre connector
8. Remove vinyl at end of feed-line and prepare centre and braid
9. Solder centre connector of feed-line to one side of braid at c
10. Solder braid of feed-line to other side of braid at c
11. Position connection inside frosting cup and completely fill with hot glue
12. When still warm put lid in place and glue edges from back side
13. Let completely cool then drill a hole in upper section for mounting
14. Go to point b and remove one inch of vinyl
15. Carefully open a small section of braid and pull centre insulator up
16. Remove insulation on centre wire
17. Reposition braid over centre wire neatly and solder together
18. Cover entire area with hot glue and let cool
19. Repeat steps 14 through 18 at point d
20. Solder together centre and braid at points a and e
21. Cover these points with hot glue and let cool

Mounting and Tuning

1. Take some strong small nylon rope and install it on each end by using half hitches in about a one foot area at the end dipole section at a and e also attach a small rope in the hole that you drilled in the frosting container.
2. Install plastic insulators at end of rope
3. Hang antenna up using strong rope and connect to radio and SWR meter
4. Check SWR and determine resonate frequency (lowest SWR)
5. If tuning is necessary lower longer/ higher shorter if SWR is flat at 1.875 then you need to remove equal length on each end and rehang and check SWR.  If the SWR is flat at 1.950 then you need to lengthen the antenna and you can do this by simply soldering a length of standard dipole material to the end.