"Getting the Most From Your Hand Held Transceiver" Date: Wed, 03 Dec 97 17:12:51 GMT From: Ed.Harris@p3006.airnsun.pcbuddy.com (Ed Harris) To: sarinfo@mindlink.net Subject: Handy Comm Hints Copyright 1997, Nonprofit reproduction permitted with source attribution. C. Edward Harris, KE4SKY Asst. Emergency Coordinator, Fairfax Co. ARES When limited to "barefoot" operation with a "rubber duck" on simplex, hand held tranceivers (HTs) are not adequate as a primary rig for emergency communications. I started with an HT when I first got my license and now generally recommend 50 watt 2-meter mobiles as a first rig for amateurs, but they don't work for everyone. If all you have is an HT, the following will help you "make the most of it," whether it is amateur, marine or public safety high band VHF or UHF GMRS or public service band gear. An amateur HT does make perfectly good sense for: 1) Anyone who doesn't drive; 2) Commuters who use public transportation; 3) Controlling a dual-band mobile in cross-band repeat or; 4) As a "spare," backup or loaner. FACTS ABOUT HT ANTENNAS National Bureau of Standards tests of Public Safety high band and amateur 2-meter antennas indicate that a "rubber duck" has -5db "negative gain" compared to a quarter wave held at face level. In terms of effective radiated power (ERP), a 5w HT with rubber duck antenna, at face level radiates only 1 watt. Placing the HT on your belt attenuates the signal -20db further, reducing ERP to only 50 milliwatts! UHF results are little better. This simple helical spring is intended to withstand rough handling, but is not indestructible. Flexible antennas used on fire lines for several weeks showed a 60 percent failure rate. SAR users should expect similar results, based on EMS and police service experience. California RACES recommends that flexible amateur antennas be replaced annually or when they begin to show any apparent kinks or wear to visual inspection. Replacing a defective antenna not only improves your signal, but it may save the final power transistors on your radio from premature failure when you really need it! A simple, inexpensive and effective expedient which improves a "rubber duck" is the "tiger tail". You can make one of these using a quarter-wave (18-3/4" for 2 meters) piece of #14 through #20 braided wire, crimped and soldered to a battery clip. Reinforce the soldered connection with shrink wrap 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. Numerous antennas work much better than the "rubber duck" that comes with an HT. A flexible 1/4 wave or telescoping half-wave antenna are recommended. A 1/4-wave used with a ground plane, or at face level with a counterpoise has "unity" gain, a 5 db improvement over a rubber duck, because all of the signal is radiated. Using an HT at 5 watts with a 1/4 wave mag mount on an improvised ground plane, or telescoping half wave with a "tiger tail" improves simplex readability. In marginal locations a telescoping half-wave is a better performer. A half wave used without a ground plane has the same unity gain as a 1/4 wave when used with a ground plane. Adding an effective ground plane or counterpoise to a half-wave produces 2 db of gain. Telescoping antennas work best operating stationary or in the open, avoiding side impacts or rough handling. A telescoping half wave can 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, mobile in city traffic. Avoid prolonged mobile use at high speed, because excessive flexing will loosen the internal electrical connections. Never collapse a telescoping antenna by whacking it down with the palm of your hand. Gently pull it down with your fingers. If you note any wobbling or looseness, replace the telescoping radiator, if possible or replace the 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 because telescoping antennas are usually limited to a single-band. Dual-band flexibles are usually optimized for one band and merely "acceptable" on the others. Most approximate a 1/4 wave on 2 meters and a 5/8 wave on 70 cm, but how efficient a particular antenna is can be determined only by testing. If you want to buy one emergency HT antenna, without risk or experimentation, the telescoping half-wave, flexible quarter wave and quarter wave mobile magnetic mounts offer the best "bang for the buck." A telescoping half-wave boosts practical simplex range of a 5 watt, 2-meter HT from the typical mile or so with a rubber duck to 3 miles or more over rolling terrain. Adding a tiger tail further improves copy at the fringes, extending simplex range to 5 miles or so. Whatever HT gain antenna you get should be rated for 25W so that it can also serve as an emergency antenna for a mobile rig at medium power or with a brick amp. A 1/4 wave mag mount with 15 ft. of coax and a female UHF to male BNC adapter can be used with an HT, connected to a brick amp or higher powered mobile rig. It works best on a car, but a suitable improvised ground plane can usually be found around the home or office, such as a metal filing cabinet, metal trash can, refrigerator, rain gutter, window air conditioning unit, balcony railing or other large metal object. An effective, portable improvised ground plane is easily constructed from a pipe floor flange, 1/4" bolts, nuts and lock washers, attaching 20" radials bent from #10 solid steel or aluminum rod. BATTERY BASICS It is highly recommended that you routinely carry two fully charged nicad packs and an extra AA battery case, so you can continue to operate if you can't recharge your nicads. It is important in cold weather to keep nicads warm, not exposed on your belt. Adapter cords enabling you to use DC power taken from an auto cigarette lighter plug or a gel cell battery, are needed for extended operation. The popular cigarette lighter plug power cords are often unreliable because auto lighter sockets are often contaminated and not the best conductors. They also vary in size, so the plug can vibrate loose. As an alternate source of power, everyone should still have one, because they are ubiquitous and in a pinch, much better than nothing. Commercial power packs, such as Quantum, are excellent, but expensive. Your group can make its own using Yuasa NP2-12 or similar 12-volt, 2 amp-hour gel cells. These fit in a coat pocket, run an HT all day or power a 25-watt VHF amplifier for 3 hours at a typical duty cycle. Purchased new they are expensive, but medical facilities use them to power diagnostic instruments and they are replaced on schedule before they are worn out. Lead acid batteries require disposal as hazardous waste, unless recycled or reused, so a hospital's "donation" to your ARES / RACES organization reduces their disposal cost. Your EC could write a letter to the purchasing agent or environmental officer of the local hospital, explaining how gel batteries a few years old, which they discard are useful to provide power for your emergency communications activity. It may be possible to obtain a useful 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 administrator. Assemble auxiliary power cords to power your HT and small brick amp following the standard wiring configuration shown in the ARRL ARES Resource Manual. Use twin lead AWG12 to AWG18 gage "zipline" with Molex Series 1545, 2-pin polarized connectors and .093 pins. In ARES practice the female pins are assembled into the male plug and the male pins into the female receptacle. The plug, receptacle and pin sets cost $0.99 each from Radio Shack, Part No. 274-222 and are rated at 8 amps, which is adequate to power small brick amps up to 35w output. Electronic suppliers carry the genuine Molex parts in bulk. These are rated at 11 amps and suitable for mobile rigs up to 50w. Wiring is simple. The end of the two-pin Molex plug in cross section resembles a little 2-story house with peaked roof. It's easy to remember the proper polarity by using the word associations "red roof" and "black basement," or "pointy positive" and "flat black." Crimp the tabs to hold the wires in place before soldering them to ensure a strong connection. After inserting the pins into the plug and receptacle, check fit of the assembled fitting and reinforce the wires behind the plug and receptacle with heat shrink or tape. On the battery ends attach crimp type .187" female tab terminals to fit the male tabs on the battery. Wire a plug receptacle onto the leads of a 12-15v, 500mah to 900mah charger. A depleted 2 ah battery is restored in 4 to 6 hours, but larger gel cells may be continually trickle charged without harm. You can rig two sets of cords directly from your car battery to power an HT and your brick amplifier without using the cigarette lighter plug. This is a good arrangement for using an HT in the vehicle during your commute and taking it with you when you park the car. Splice AGC type fuse holders on the red or "hot" leads, as close to the battery as possible. Use a 2 amp fuse for the HT and 10 amp for a 25w-50w brick amp. Use a heavier gage wire than needed to reduce voltage drop, and use different sizes, such as AWG 16 or 18 for the HT and AWG 14 or 12 for the brick amp, so the two cords are easily distinguished by both sight and feel. HAND HELD DUTY CYCLE LIMITS If you subject today's HTs to frequent full power, 5w transmissions of several minutes duration they 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 their maximum RF output, or 30 seconds of transmit to 2 minutes of standby. After I first got my license, I burned up three sets of "finals" in less than a year with long winded QSOs using a Radio Shack HTX-202 which produced 8w when powered at 13.8V from my auto cigarette lighter plug! When the warranty ran out, I replaced it with a Kenwood TH-22 and repeated the same result. Kenwood's Virginia Beach service center politely admonished me that I was "exceeding the recommended duty cycle" and should buy a mobile. I followed their advice and am satisfied with my two Kenwood mobiles, but I sought out other HTs and pass that advice along. 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. My advice is that 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 afford to replace or supplement your hand held with a mobile rig, my advice is to get a small 25-50w brick amp to do the work. This keeps your HT from overheating, and helps ensure a solid copy signal for $100 or less. ADVICE ON BRICK AMPLIFIERS An ideal small amp for an HT owner to upgrade his portable ARES equipment, at modest cost should weigh under a 1½ pounds, be capable of 10 to 15w output when driven by an HT at ½-1w, or 30 to 40w output when driven by the same HT at normal 2 or 3w output from its 7.2 volt nicad battery pack. It should draw no more than 8 amps current at its maximum rated output, enabling it to operate safely from the .093 pin Molex Series 1545 connector or fused cigarette lighter plug. An FM-only brick amplifier without preamp is fine, unless you have a portable all-mode, weak signal rig, with notch or cavity bandpass filter to suppress intermodulation distortion from commercial paging transmitters and the like. Brick amps which have been satisfactory in our group experience are the Mirage B-23, the dual-band Mirage BD-45, and RF Concepts Mini 144. There are larger amps producing 100+ watts output when driven by an HT, but their size, 5+lb. weight and 20+ amp power consumption lend them more to base or rover, wide area simplex coverage, than to local "backpack portable" ARES / RACES operation. Be wary of bargain, "no-name" amps you'll see at ham fasts or in discount catalogs. Some are not aligned properly for the entire U.S. 2-meter band, many lack thermal protection circuitry for over voltage, overdrive or high VWSR or simply may have an inadequate heat sink and will overheat and quit. A friend bought a Chinese amp from MCM Electronics for $69 which worked fine on packet, some repeaters and on simplex from 146.415 to 146.585, but did not function at all above 147 MHZ. MCM took it back and refunded his money cheerfully. Though aware of duty cycle limitations in small amps having minimal heat sink, I still wanted a tiny mini-amp for my "Go Kit," to boost an HT when really needed. I found a Maxon CA-1461, which is only 1.7"x1.7"x5.5" and weighed 9 ozs. and bought the last one that Associated Equipment Sales had displayed at the Gaithersburg ham fest. It was reputed to be for 2 meters, but it did not produce rated output as received. The seller didn't offer a refund, but told me to return it to Maxon. I e-mailed Maxon and they told me this accessory for a discontinued commercial product was never marketed for amateur use, but was type accepted as Class C at 136-172 mhz had an adjustable 7 mhz. passband within that window. Beyond that they said I was on "my own." I asked KE4VIH open it up, since he had access to a lab full of test equipment. As it came from the factory it was aligned for 153-160 mhz., marine VHF and Public Safety high bands, but it had an adjustable input potentiometer which came down easily to 2 meters. A minor glitch was that the "Tx In" and "Ant Out" ports were unmarked. The jumper provided had male BNC and UHF connectors which led me to hook it up reversed! Fortunately, nothing inside was damaged. We used a double-male BNC to connect the HT to the input, put a dummy load on the UHF output and soon got it working. It now produces 15w out with 1w of drive, 25w out for 2w and 35w for 5w. It doesn't get uncomfortably warm after five minutes of continuous key-down at 15w into a dummy load, but gets somewhat warm after 3 minutes at 25w, and "hot" after 2 min. at 35w as you might expect. It did well for transmitting medlog data during the 22nd Marine Corps Marathon, but a longer trial is needed before recommending that you search ham fests to find one to "mod." Unless you know how to modify commercial gear, my advice is to buy 25-40 watt amp of a known brand, with an ample heat sink, from a supplier that backs the product rather than seeking the smallest "box" at the lowest price. For further emergency communications information see the Virginia ARES web page at http://www.aresva.org Reply To: ed_harris@p3006.F120.n109.z1.fidonet.org '73 de KE4SKY, Regards, Ed -------------------------