The ARES E-Letter
September 26, 2008
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Rick Palm, K1CE, Editor
+ Coaxial Antenna for EmComm
There are many antennas that may be purchased or constructed and carried in your emcomm kit.
Small dipoles, J-Poles and many other antennas that can be rolled-up, placed in a zip-lock type bag and stowed in your kit. But what about the all but forgotten coaxial antenna?
| The coaxial antenna is basically a quarter-wave piece of 52 Ohm coax. |
| (RG8X or RG174 are my cables of choice). Construction for a two meter coaxial antenna follows: |
| 1. Remove 19 inches of the outer jacket from a four foot or long piece of coaxial cable. |
| 2. Carefully remove about 18 inches of the exposed shield. The shield will be used as a sleeve. |
| 3. Slide the shield (removed in the above step) up the coax from the far end to the point where the jacket begins and the one inch of shield remains. |
| 4. Using a relatively low Wattage soldering iron, tin the top of the sleeve. |
| 5. Carefully fold the one inch of shield over the top of the sleeve. |
| 6. Using the low Wattage soldering iron, solder the shield the top of the sleeve. |
| 7. Check all work. What you should see is eighteen inches of dielectric along with the center conductor and eighteen inches of sleeve with any length of coax after the sleeve. |
| 8. Check for shorts and opens with an Ohm meter. |
| 9. Add the coax connector of your choice to the end of the length of coax. |
| 10. Check for shorts and opens again. |
| 11. Carefully affix a loop of string or a plastic wire tie to the top of antenna using a good quality tape or heat shrink. The whole antenna can be covered with heat shrink. You may utilize the extra one inch of wire at the top by stripping of the dielectric from the top and soldering the wire into a loop. The extra one inch must be removed or utilized so as not to be part of the antenna. |
| 12. The antenna can now be hanged from the support of your choice and when finished, it can be stowed very easily. |
Some additional thoughts:
Coaxial antennas are quite useful above 30 meters. However, they become physically unwieldy below 30 meters. This type of antenna does have a lower angle of radiation than the popular J-Pole with the added bonus of some slight gain.
If the numbers look familiar, that is because we are dealing with quarter-wavelength sections.
The upper portion is a quarter-wavelength and the lower (sleeve) is a quarter-wavelength.
- Jay Musikar, AF2C, District EC, East-Central District, Northern Florida Section
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