- Written by Brian Keahl
- Category: Emergency Communications
- Published: 31 May 2018
- Hits: 13497
Emergency Communications deployment has similarities to camping and backpacking trips, where you need to pack everything you need with you without overloading yourself. Striking the proper balance is challenging, because no matter how hard you try you will usually find something you should have packed and something you should have left behind, because we never know what the requirements of the deployed location will be.
It's safe to say that one item likely to be on any deployment list is some form of enhanced antenna to improve the ability to reach out to distant repeaters, or even function as an ad-hoc cross-band repeater.
Arrow makes a great dual band J-pole that breaks down to be pretty portable, but requires a pole to be mounted to, as is the case with most commercial antennas. It's possible to bring a tripod along, or some type of mount that can be attached to your vehicle, but that may require your deployment be restricted to a parking lot or your vehicle. Sometimes that will be the case by necessity, but it does isolate you from your served agency members.
Ideally we'd want to have an easy to deploy antenna that is light, compact, and easily deployed. One solution is the "Roll-Up" antenna, affectionately called the "Slim Jim". Slim-Jim antennas, not to be confused with the tasty treat, are constructed using ladder line, a little solder, and some coax with a connector, much as you'd construct an HF dipole antenna.
While many Amateur Radio operators make their own HF antennas, most tend to purchase their VHF/UHF antennas, even though they can and will operate on the same principles as an HF antenna. Remember, an antenna is nothing more than a resonant conductor, be it wire or pipe made of steel, aluminum, or copper. For those that have built tape-measure Yagis, this requires a bit more soldering, but less mechanical assembly work.
While it doesn't have great gain, the SlimJim does have the benefit of being very inexpensive to make, can be tuned fairly easily, and there is even a design for a dual-band version that could be used to setup on-the-fly cross-band repeaters as well as to communicate with them (see graphic).
Since the antenna is end-fed, you can throw a rope or thick twine over a tree limb or other above-ground object and tie it to the end of the Slim-Jim and hoist the antenna into the air! Because of its construction, it can be rolled up into a small coil and easily packed away.
An antenna would greatly increase the range of an HT, particularly if operating from inside a building. With this type of antenna the coax could be run out a window or door and an HT or base station operated from inside a structure. There is, as always, a trade-off. Gain is not as good, particularly on 440mhz, as would be with other antennas.
For more information, and instructions on how to construct your own flexible/portable SlimJiim antenna, visit http://www.qsl.net/sterling/Activities/20170301_J-Pole_Build/Emergency_antennas.pdf