Glendora Emergency Response Communications

EMERGENCY OPERATIONS & YOUR HT, Part One

May 29, 2010

Here is a older article on Emcomm that is still relevant today.  N7YLA

Jun 22, 2004

March 23 , 2004

This Bulletin is Courtesy Santa Clara County, California ARES/RACES

Before I begin, I would like to give credit to C. Edward Harris, KE4SKY, AEC for Fairfax County ARES in Virginia for his article on "Getting the most from your Hand Held Transceiver." Much of this script has been taken from that article. Some minor editorial changes have been made to make it more readable over the air.

HT Antennas

It shouldn’t come as a surprise to anyone that when limited to "barefoot" operation with a "rubber duck" on simplex, HTs are not adequate as a primary rig for emergency communications. The National Institute of Standards and Technology (NIST) ran some tests on Public Safety high band and amateur 2-meter antennas. They found that a "rubber duck" has negative 5db gain compared to a quarter wave antenna held at shoulder height. In terms of effective radiated power (ERP), a 5w HT with rubber duck antenna, held at shoulder height would actually radiate 1.5 watts. Placing the HT on your belt attenuates the signal another 20db, reducing ERP to only 15 milliwatts! UHF results weren’t found to be much better.

A simple and inexpensive improvement that can be made to the "rubber duck" is the addition of what is called a "tiger tail". You can make one of these using a quarter-wavelength (19-1/4" for 2 meters) piece of #14 through #20 stranded wire, crimped and soldered to a battery clip. Reinforce the soldered connection with heat shrink tubing or tape to resist flex. Clamped to the outer collar of the BNC connector on your HT antenna, it acts as a counterpoise so that RF from the HT doesn’t couple with your body. A "tiger tail" is directional and can be used to change both radiation angle and direction. It gives best simplex performance when pointed in the general direction of the station you are trying to "hit".

Almost any antenna works better than the "rubber duck" that comes with an HT. A flexible ¼ wave or telescoping half-wave antenna are both improvements. A ¼-wave used at shoulder height with a counterpoise has "unity" gain, which is a 5 db improvement over a rubber duck, because most of the signal is radiated. Using an HT at 5 watts with a ¼ wave mag mount on an improvised ground plane, or telescoping half wave with a "tiger tail" improves simplex readability even further.



In marginal locations, a telescoping half-wave is a good performer. A half wave used without a ground plane has the same unity gain as a ¼ wave when used with a ground plane. Adding an effective ground plane or counterpoise to a half- wave produces roughly 2 db of gain. A telescoping half wave can also be attached to a coax jumper and pulled into a tree, dangled out a window, attached to a window pane with suction cups or used with a window clip door mount.

Telescoping antennas work best when operating stationary or in the open, avoiding side impacts or rough handling. Extend and retract the radiating elements very carefully. If you note any wobbling or looseness, replace the telescoping radiator, if possible, or replace the entire antenna. Keep a close watch on your HT’s connector also. It can become loose after extended use of a telescoping antenna.

Flexible antennas are safer when working in close quarters around people and are more durable when walking through dense vegetation during search and rescue operations. They are a good choice for dual-band transceivers, but are usually optimized for one band and merely "acceptable" on the other. Most approximate a ¼ wave on 2 meters and a 5/8 wave on 70 cm. How efficient a particular antenna is can be determined only by controlled testing.

If you want to buy one emergency HT antenna, without risk or experimentation, the telescoping half-wave, flexible 5/8 wave or quarter wave mag mount all offer the best "bang for the buck" in my opinion. A telescoping half-wave boosts practical simplex range of a 5 watt, 2-meter HT from several miles with a rubber duck to many miles over suburban terrain. Adding a tiger tail further extends readable simplex range under the same conditions.

Whatever antenna you choose, try to find one that is rated for at least 25W so that it can also serve as an emergency antenna for the HT with a power amplifier at medium power. A ¼ wave mag mount connected to a power amplifier works best on a car, but a suitable improvised ground plane can usually be found around the home or office. A metal filing cabinet, rain gutter, refrigerator, balcony railing or other large metal object may work just as well. If all else fails, place aluminum foil over a large piece of cardboard .

A good possibility for Fixed position Emergency Operations is the so-called Roll Up J-pole . It’s made from 300 Ohm TV Twin-lead and should give you several dB of gain over a rubber duck. We will have plans available for this very inexpensive antenna at the next meeting.

Another antenna that is a good performer for fixed operations is the " Copper J-Pole ". They are generally available at swapmeets for a reasonable price, and plans to build them are found on the internet.. Attach it with hose clamps to the top of two 10 foot nested sections of inexpensive cyclone fence top rails and place it in a TV antenna roof mount tripod. You can weigh down the tripod by bolting the leg brackets to concrete building blocks. Be sure to use a carpenters level to make sure everything is straight. This makes a very nice fixed station temporary antenna with good gain.

73 DE KF6DSA