Santa Clara County, California
ARES/RACES

EMERGENCY OPERATIONS & YOUR HT


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.

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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 (back when they were still the NBS) on Public Safety high band and amateur 2-meter antennas. They found that a "rubber duck" has -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.

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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".

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Almost any antenna works better than the "rubber duck" that comes with an HT. A flexible wave or telescoping half-wave antenna are both improvements. A -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 wave mag mount on an improvised ground plane, or telescoping half wave with a "tiger tail" improves simplex readability even further.

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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 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.

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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.

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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 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.

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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.

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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 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 .

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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. I've used mine for the past year and one-half as a base antenna and have been quite happy with it. It is well worth the money spent (~ $20). Let me reset and I'll give the dimensions.

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Would anyone like any of the dimensions repeated?

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Another antenna that is a good performer for fixed operations is the " American Legion J-Pole ". They are generally available at both the Foothill and Livermore Flea Markets for a reasonable price. Attach it to the top of a 10 foot section of PVC pipe and mount this to a camera tripod. Attach weights to the legs for stability. This makes a very nice fixed station antenna with good gain.

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BATTERY BASICS

For Emergency Operations, it is highly recommended that you carry two fully charged nicad packs and an extra AA battery case and batteries. The nicads will power your HT for at least the first full day of operations and the AA's will allow you to continue to operate if you can’t recharge your nicads. It’s also important in cold weather to keep nicads warm, and not exposed on your belt.

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As an alternate or primary power source, use 12-volt, 2 Ahr or higher Sealed Lead-Acid or Gel Cell batteries. They fit in a coat pocket, run an HT all day or power a 2 meter mini-amp for 3 hours at a typical duty cycle. Sealed Lead-Acid or Gel Cell batteries have many advantages. They will allow you to:

Operate when other forms of power are not available

Operate longer than with NiCad or Alkaline batteries; 1–3 Ahr batteries are still small enough to be hand carried.

Operate mobile, portable or fixed at a higher output power

Operate at a lower cost; Gel Cells and SLA’s are less expensive than NiCads or alkalines.

Operate with fully charged batteries at all times; It’s possible to keep these batteries on a "smart" charger continuously.

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Sealed Lead-Acid batteries are used to power medical diagnostic instruments, alarm systems and Un-interruptible Power Supplies (UPA) just to name a few. Depending on the criticality of the application, some organizations replace their batteries on a regularly scheduled basis well before they are worn out and require disposal as hazardous waste. EC’s should write or call local hospitals, explaining how batteries they discard are useful for emergency communications activity. It may be possible to obtain a quantity free for the asking, with no more trouble than signing a hand receipt to satisfy the environmental officer and writing a thank you letter to the hospital administrator. Remember, a hospital’s "donation" to your ARES group eliminates their disposal cost.

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Besides hospitals, and alarm companies, batteries are also available locally at reasonable prices. For example, Halted Specialties usually carries new 12V, 7Ahr batteries for around $20. For those wanting to buy a complete commercial package, HRO sells the "Hot Pocket" which is a 12V, 2Ahr SLA for $78. It comes with its own pouch for attaching to your belt and a wall charger.

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If you decide to use Sealed Lead-Acid or Gel Cell batteries, you'll need a battery charger. 12 V Battery Chargers are available from various sources:

Jade Products offers a "Smart Charger" for charging Gel Cells and SLA's. It’s $126.95 in kit form.

A & A Engineering also offers a "Smart Charger" for Gel Cells and Lead-Acid batteries. Their charger is $59.95 in kit form or $79.95 finished .

You can also use so-called "Wall Warts", but the general consensus is that your batteries won't last as long on these inexpensive chargers.

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Of course, you can always build you own. Two very good articles are the:

June ‘87 issue of QST entitled "A New Chip for Charging Gelled-Electrolyte Batteries"

This article uses the Unitrode UC3906 "Smart Chip".

March ‘94 issue of QST entitled "A Lead-Acid Battery Charger"

There is also some very good information available on the internet. I have several good URL's that I can pass along if anyone is interested.

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http://www.unitrode.com Unitrode – Home of the UC3906 "Smart Chip"
http://www.benchmarq.com/ Benchmarq chargers
http://www.ibexmfg.com/ Ibex battery chargers
http://www.yuasabatteries.com/ Yuasa "Battery Handbook and Technical Guide"
http://www.electriciti.com/batteri/pwrson1v.html Powersonic batteries

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AUXILIARY CONNECTIONS

Power cords for connecting to automobile cigarette lighter plugs or gel cell batteries will be needed for extended operation. Be aware that cigarette lighter plug power may be unreliable due to contaminated cigarette lighter sockets. Also, the sockets themselves vary in size, allowing the plug to vibrate loose. As an alternate source of power, however, everyone should still have the capability since they are readily available.

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Be sure to assemble any auxiliary power cords for your HT or small power amps following the standard wiring configuration shown in your respective SPECS or SVECS manual. The configuration that follows is taken from the ARRL ARES Resource Manual. The SVECS manual agrees with this configuration; I’m not certain of the SPECS manual. This configuration uses twin lead 12 to 16 gauge "zipline" with Molex Series 1545, 2-pin polarized connectors and .093 diameter pins. In ARES practice, the female pins are assembled into the male plug which is attached to the power source, and the male pins into the female receptacle which is attached to the rig. This description will make more sense to you when you have the parts in front of you and are assembling the connector.

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The plug, receptacle and pin sets are available from Radio Shack, Part No. 274-222 and are rated at 12 amps, which is adequate to power small amplifiers up to 50w output. Wiring is simple. The end of the two-pin Molex plug in cross section resembles a little 2-story house with peaked roof. Remember proper polarity by using the word associations "red roof" and "black basement" for the positive and negative terminals respectively. Crimp the wires in place before soldering to ensure a strong connection. After inserting the pins into the plug and receptacle, check the fit of the assembled fitting and reinforce the wires behind the plug and receptacle with heat shrink tubing or tape.

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For re-charging the battery, attach crimp type .187" female tab terminals to fit the male tabs on the battery. The other end of the battery connection will go to a standard cigarette lighter socket. Next, wire a plug onto the leads of a 12-15v, 500 to 900mah charger. A depleted battery can be restored in 4 to 6 hours by plugging it into your car’s battery. Gel cells and SLA's larger than 5 Ahr may be left on a 12-14V DC "smart" charger of 1 amp without harm. A word of caution here . . . . . . become very familiar with your particular charger and the types of batteries that you intend to charge before leaving a charging battery unattended. A malfunctioning charger can create a very BIG mess very quickly.

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HAND HELD DUTY CYCLE LIMITS

If you subject compact HTs to frequent full power 5w transmissions of several minutes duration they will overheat and the final power transistors may fail prematurely. Kenwood and Yaesu state in their service manuals that their HTs are rated for 20% duty cycle at maximum RF output, or 30 seconds of transmit to 2 minutes of standby.

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Of the popular 2-meter HT’s, Standard does not restrict duty cycle on theirs, rating their amateur hand helds equal in that respect to their aviation, marine, commercial and public safety portables. Unless your HT is a Standard, older Icom or converted commercial gear, it is best to use your HT mostly on medium or low power for long winded rag chews and restrict full power 5w use to short transmissions to save the finals. If you have a need for high power transmissions of several minutes duration and can’t replace or supplement your hand held with a mobile rig, I would advise getting a power amplifier to do the heavy work. Just remember to reduce your HT's output power going into the amplifier, otherwise, you will still burn up your finals.

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 ADVICE ON POWER AMPLIFIERS

An excellent way for HT owners to upgrade their portable ARES/RACES equipment is to purchase a power amp. An ideal amp should weigh less than 1 pound, be capable of 10 to 15w output when driven by an HT at 1w, or 20 to 40w output when driven by the same HT at 2 to 3w output. It should draw no more than 8 amps of current at its maximum rated output, enabling it to operate safely from the .093 diameter pin Molex Series 1545 connector or fused cigarette lighter plug.

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An FM-only amplifier without a preamp will be adequate in most cases. A preamp tends to accentuate intermod due to paging transmitters. Unless you equip your portable station with a notch filter and/or cavity bandpass to suppress this intermod, the preamp will serve no useful purpose. Be wary of bargain "no-name" amps you see at hamfests or in discount catalogs. Some are not aligned for the entire U.S. 2-meter band, many lack thermal protection circuitry for over voltage, overdrive or high VWSR or simply have an inadequate heat sink and will overheat and quit.

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OK, this concludes "Emergency Operations and your HT." Are there any questions?


This page was last updated 04/21/02