Double bazooka antenna: The BAZOOKA antenna is a half-wave antenna that works efficiently in a band with no change in ROE. The design of the BAZOOKA antenna was developed in the 1940s in the United States as a radar antenna , being modified for the use of radio amateurs in the 1950s . Over time Double Bazooka has been shown to outperform a standard single band dipole. It is a very popular antenna among radio amateurs .
Summary
[ hide ]
- 1 Design advantages
- 2 Features
- 3 Construction
- 4 Criterion for calculating it
- 5 Steps for its construction
- 6 Sources
Design advantages
This antenna design does not require the use of a balun , feeding directly with a 50 ohm coaxial cable . The BAZOOKA dipole is 98% efficient with nominal ROE readings less than 2: 1 across the entire working band. Since this antenna does not accumulate static charges that affect the metal wire , it supposes a reduction of noise with respect to other vertical antennas or dipoles. This antenna can be mounted in inverted “V” for optimal results, forming an angle between 90 and 120 degrees, with vertical polarization with low radiation angle, ideal for DX .
characteristics
- Similar in size to a half wave dipole.
- Significantly improves reception compared to a dipole. 99% to 100% efficiency at design frequency.
- Impedance 50 ohms.
- Great bandwidth. 3: 1 on a dipole. Fully covers the operating band.
- It does not radiate harmonics at the working frequency. Solve ITV problems.
- With RG58U coaxial cable it can support a power of up to 1 Kw.
Building
As you can see in the figure, it is a half wave dipole formed by the external conductor of the coaxial cable , in combination with the open line terminal sections. The outer conductor or shield of the coax opens to the center, from where the power line connects. The inner conductor does not radiate and forms a short-circuit ¼ wave resonator which, in resonance, has a very high resistive impedance at the supply point. At frequencies other than resonance . The open end line that complements the dipole, for your comfort, can be built with a 300 ohm flat tape that is normally used as a drop line fortelevision . The ends of flat ribbon can be replaced by wire and in such a case, keeping the characteristic proportions of the coaxial cable and following the following formula, it can be built for any frequency .
Double Bazooka design
Criterion for calculating it
We will use the Formulas:
- 2 / fMhz = total length.
- 06 / fMhz = length of the coax.
- 57 / fMhz = length of each side of flat tape.
Steps for its construction
- Short-circuit both ends of the 300 ohm flat ribbon and solder, taking care to cut off the excess tips.
- Solder all together, the mesh and the center conductor of the coaxial cablewith both conductors of the 300 ohm tape .
- Slice an inch of plastic covering the coaxial cable. Cut the mesh of the horizontal coaxial cable exactly in the center and separate both sides so that it does not make electrical contact. Do not damage the dielectricor the central conductor of the coaxial cable, which must pass from side to side. With the cut meshes two points must be formed. Solder one end to the center conductor of the drop coaxial cable and the other end of the mesh weld it to the drop coax cable.
- The coaxial drop cable can be RG58U and any length. Connect directly to the 50 ohm input on the transceiver.
The Standing Wave Ratio should have a value of 1: 1 at the design frequency and at the ends of the 80m band it should not be beyond 1.5: 1. If the ROE is too far from these values, there is a problem. Review everything. To finish the antenna, conveniently seal all surfaces exposed to rain or moisture with some product, silicone , poly foam with gasoline , wax or paraffin , any product that does not allow moisture to pass through. There are several practical ways to hang this antenna and these will depend on the skills and ingenuity of each colleague and on the frequency that one wishes to operate.