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How Use of a Mobile Amplifier-Charger Gives Mobile Performance, plus Portability.

In this age of sophisticated radios, many land-mobile applications that previously required a conventional mobile unit are being met through the use of a portable--and for good reason. Despite its limited power output, decreased coverage and rapid battery consumption, the portable offers the user one powerful advantage over any mobile--versatility. And when combined with a mobile amplifier/charger, the above limitations are virtually eliminated.

The key to user satisfaction lies in the ability to fulfill communications needs through efficient and cost-effective system design. Today's availability of mobile amplifier/chargers offers a choice between the solely mobile and purely portable in an economical package that users find attractive.

When a user's requirements indicate the need for portables--plus the necessity for occasional enroute communications--the case for mobile amp/chargers is apparent. Or, when one's system criteria point toward mobile-radio application, yet one desires the versatility of portable communications, again the mobile amp/charger enters the picture. As will be shown later, many applications fit these formulas. Mobile amplifier/chargers exist to solve a wide range of problems.

As their name implies, mobile amp/chargers contain two primary circuits. In the order of their problem-solving importance, the first one combats battery drain with a fast/trickle charger that maintains a full charge whenever the portable finds itself dressed as a mobile. Easily the number-one enemy of portable popularity, dead batteries are of constant concern to the portable user.

Secondly, by adding an RF amplier, vehicle antenna, dynamic microphone, audio amplifier and speaker, the portable emulates even the finest of mobile radios. Plus, given the additional ground plane for antenna propagation, the portable's coverage area expands to meet demand.

All of this capability is attainable at an average saving of 35 percent compared to the price of separate mobile and portable. (Refer to the cost-comparison chart--Figure 1.) And installation time is reduced because such units have an internal RF amplifier rather than an auxiliary amp.

Although many manufacturers' product lines don't offer the option of a mobile amp/charger, they're often available via independent suppliers. There are now mobile amp/chargers for more portables than ever before, including Standard, Regency, E.F. Johnson, Wilson, Henry, Yaesu, Aerotron, Shinwa, Pathcom, Bayly, Icom, Uniden and Sonar.

In operation, a portable's RF transmit/receive signals are passed into the mobile amp/charger through low-loss coaxial cable to the antenna switch and RF sensor. When the sensor detects the presence of transmitted RF energy, it routes the signal into the broadband RF amplifier for further amplification. Typically, the power output to the antenna will be 20 to 45 watts (140 to 174 MHz) or 8 to 22 watts (450 to 470 MHz), depending on the portable's output level. Before reaching the antenna, the transmitted RF energy passes through a low-pass filter to reduce harmonic generation and match the impedance of the antenna system.

During the periods that the RD sensor is not detecting transmitted signals, the antenna switch allows a direct signal path for received signals to pass into the portable's receiver circuitry. Any signal attenuation that is induced by the connectors and antenna switch is masked by the enhanced reception provided by the vehicular antenna.

Speaker audio is routed through the portable's speaker/microphone jack to the audio amplifier circuitry. Here, the audio signal is boosted and filtered to drive the mobile amp/charger's speaker. Many vehicle environments benefit greatly from the availability of five watts of crisp, clear audio, rather than the portable's humble 500 milliwatts.

As previously mentioned, a portable's number-one drawback--battery drain--must receive constant attention. Ignoring it places the user in jeopardy of inadequate communications. Quality mobile amp/chargers address this condition with two methods of action. First, by monitoring the battery's voltage, the charging circuitry determines the level of discharge. Then, depending upon the condition, the charging circuitry sets in motion the process of bringing new life to the weakened power source.

If the battery is seriously discharged, the charger's control circuitry selects "fast-charge" mode. This will present a charging current (typically 140 milliamps) to the battery's terminals. Normally, this mode will bring the portable's battery to full charge within an hour.

Also, when the battery is fully drained, the charging circuitry allows immediate use of the portable through a battery-eliminator circuit. In this manner, while the battery is being charged, the portable is given full access to input voltage from the vehicle's battery.

When the control circuitry senses a battery condition near full-charge potential, it engages the charging components into "trickle-charge" status. In this configuration, the battery is held in a "maintained" condition with 50 milliamps of charging current.

The control circuitry also carries the responsibility of informing the user--through front-panel lights--which charging mode is being assigned. If the charger is in the fast-charge condition, the user must be made aware that the battery is not at full potential, and that if the portable is then used out of the charger, inadequate performance might result.

In addition to the internal electronics of a mobile amp/charger, the mechanical design is crucial to satisfactory performance. Only through well-defined engineering can the unit properly serve the user. It should allow easy, but sure, mounting of the portable into the "boot." Also, battery contacts should make positive connection with the charger's fingers.

The applications for mobile amp/chargers are quite varied. Statistically, the breakdown of users is illustrated in Figure 2. As can be seen, industrial applications make up the bulk of the usage.

Some examples of typical situations where mobile amp/chargers could solve communications problems can be seen in the following scenarios:

* A driver finds himself caught at the trough of his concrete truck as a summons comes over his mobile radio, but is unable to answer until the load is expended. Also, when at the job site, he often misses important calls while out of the cab.

* A factory security guard needs his radio with him while on his rounds. Then, upon return to the guard shack, he is required to check in and maintain radio communication with his headquarters.

* A county sheriff's department, with three vehicles and one base, rarely needs portables. However, when one is needed, it is needed immediately. The department would like to have mobiles and portables, but its budget is limited.

* A volunteer fireman is responsible for purchasing his own radio gear. He needs primary communications while enroute to the scene, but also must maintain radio availability while at home. Furthermore, it would be beneficial if portable communications could be available while working the forest fires that hit his area.

All of the above scenarios point toward one solution--mobile amp/chargers. Remote Amplifier Boosts Output

In applications requiring increased power outputs, an additional, remote power amplifier can be ganged to the mobile amp/charger's output. This can yield output levels in the neighborhood of 100 watts (UHF) to 150 watts (VHF).

When additional power is not required, the user can employ a charger-only version in the mobile application. This option offers all of the features of the mobile amp/charger, without the internal RF amplifier. Battery charge, battery eliminator, amplified speaker audio, dynamic microphone performance and increased signal strength, from the vehicle's antenna, boost a portable's performance.

Another consideration in the conventional mobile versus portable--amp/charger arena is the issue of operational education. By utilizing the same unit in mobile and portable communications, the user is only required to understand the operation of one radio, thus providing rapid familiarity.

Mobile amplifier/chargers allow simple answers to many of the unique applications that confront the land-mobile systems designer. With a properly engineered and correctly installed system, the user can realize the best of both worlds: mobile performance with portable convenience.

Companionships formed by portables and mobile amp/chargers present the ultimate in versatility, with the user as the ultimate beneficiary.
COPYRIGHT 1984 Nelson Publishing
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Copyright 1984 Gale, Cengage Learning. All rights reserved.

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Author:Gutsche, M.
Publication:Communications News
Date:Aug 1, 1984
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