First, in order to connect your radio to your antenna you will need coaxial cable with the appropriate connectors or adapters to mate with your radio. The selection of coaxial cable will depend on the weather resistance characteristics, frequency of operation, and cable length you plan on running along with some numbers on acceptable cable loss for your antenna and radio setup. Connectors are usually sized for a certain outter dimension of coaxial cable, so you will need to keep in mind what adapters are available for the cable you select. The table below should help you make a decision on cable selection:
Note that connectors on a cable are normally a male end because the center conductor is used as the male pin. This isn't true for reversed connectors as found commonly on unlicensed consumer equipment (such as WiFi) which is done to comply with FCC Part 15 Section 203 rules concerning antennas used on intentional radiators in unlicensed spectrum.
|Coax Name||Loss Per 100ft (146MHz)||Common Connectors|
|RG-174 / RG-174||13.0 dB||BNC Male (Special Order)|
|RG-174 / LMR-100A||8.8 dB||BNC Male (Special Order)|
|RG-58 / RG-58A/U||6.1 dB||BNC Male 58, N Male w/ UG-175|
|RG-58 / LMR-200||3.9 dB||BNC Male 58, N Male w/ UG-175|
|RG-8X / RG-8X||4.5 dB||BNC Male 8X, N Male w/ UG-176|
|RG-8X / LMR-240||3.0 dB||BNC Male 8X, N Male w/ UG-176|
|RG-8 / RG-8U||2.8 dB (?)||BNC Male 8, N Male, PL-259|
|RG-8 / LMR-400||1.5 dB||BNC Male 8, PL-259|
Next, you will need appropriate antenna construction materials. Depending on the type of antenna you are constructing, you may use materials such as wire, copper tubing, aluminum tubing, or other supplies. Note that in general using a larger diameter of antenna element will result in an antenna with better bandwidth characteristics.
It should also be noted that you will want to impedance match your antenna to 50 Ohms so your transceiver can apply RF efficiently. There are many ways to do this, some built into the antenna design itself, but some of the designs you may come across will need matching. Also, while we ideally want 50 Ohms, many solid state amplifiers can safely load into a 70 Ohm antenna load.
Antenna Construction Projects
We will look at a few common antenna construction projects. Our focus in this workshop will mainly be on VHF/UHF antennas due to antenna size and the availability of cheap VHF FM transceivers and the lack of VHF baluns/tuners. If you would like to build an antenna for HF operation, please check out the ARRL Antenna book, which can be checked out from the W7UQ Library by club members.
- J-Pole (50 Ohm)
- Rubber Duckie (50 Ohm)
- Inverted Vee (70-50 Ohm)
- Halfwave Dipole (75-150 Ohm)
- Quad Beam 3 Elements (20-150 Ohm)
Attaching Connector Ends
In order to attach to an antenna, a coaxial cable needs to be constructed with the appropriate RF connectors so that it can be mated with a transceiver. There are some criteria for coaxial cable selection such as power handling, attenuation/loss, characteristic impedance, etc., but for the most part RG-58 is readily available on a spool in the W7UQ Ham Shack.
There are many connector ends available such as crimped, soldered, or screw-on type.
The J-Pole Antenna
The J-Pole antenna is an easy to construct antenna that is popular for omni-directional VHF communications. It is usually made with copper tubing with common elbow and tee joints that are soldered together. These readily available materials make construction fast and relatively painless so that it can be a short afternoon project.
The Half-Wave Dipole Antenna
The half-wave dipole antenna is a standard antenna that is often used as a standard for gain or directivity of an antenna. It has 2.15dBi gain (over an isotropic antenna). It can be assembled for less than $5 if you have coax and connectors laying around. For VHF work, drip water T joints and welding/brazing rod make cheap but significant materials to produce good antennas and with a good knife, soldering iron, and wire cutters this can be made in an afternoon.