(T7A10) Boosting HT Power

T7A10  from the Technician License Course Section 1.1, Transceiver Basics:
What device increases the low-power output from a handheld transceiver?

A. A voltage divider
B. An RF power amplifier
C. An impedance network
D. All of these choices are correct

Most handheld transceivers, or ‘HT’ radios, output 5 watts or less of FM signal. This power level is sufficient for many local operating scenarios, and an HT connected to a rooftop or other external antenna on a car is often quite adequate for mobile operations in areas with accessible repeaters.  However, in many scenarios where the distance to a repeater is great or where the terrain rises and falls significantly and blocks signals, the HT power may be insufficient for reliable radio operations.  In such cases increasing the low-power output of the HT is desirable.

The correct response to this Technician Class question is pretty obvious, as only one answer refers to power amplification.  A voltage divider is a circuit that outputs a specific fraction of the voltage input to the circuit, so no direct relation to RF power increases. An impedance network is a circuit that helps to match the interfacing impedance between two other circuits to affect efficient power transfer between the circuits, but by itself it does nothing to increase the available RF power.

So, we are left with the HT radio connected to an RF power amplifier to increase the 5 watts or less that the HT can muster. For virtually every HT that means boosting the FM output on one or more bands in the VHF and/or UHF ranges. A very common scenario is the need to boost the power of a dual band HT that transmits on both 2-meter and 70-centimeter bands, or perhaps the 1.25-meter or 6-meter bands.

A typical dual band power amplifier may be purchased currently for around $200, and

Mirage BD-35 Dual Band RF Amplifier

Mirage BD-35 Dual Band RF Amplifier

sometimes less.  One popular example is the Mirage BD-35 amplifier that provides 45 watts output on 2-meters and 35 watts output on 70-centimeters.

The power supplied to such an amplifier in a vehicle should be via direct connections to battery terminals as recommended for installations in our Going Mobile article for the power supplied to any mobile transceiver. If used as a base station, an AC power supply or battery power sufficient to supply the amp will be necessary. Typically, the HT will connect to the amplifier via the antenna port, and the external / other antenna will connect to the amplifier.

AlincoDR-635

Alinco DR-635T Dual Band Mobile Transceiver

Total costs relative to a similarly powered mobile transceiver should be considered. For instance, a dual band mobile transceiver with equivalent power output to the amplifier may be acquired new for a bit over $300, and significantly less if used.  One example is the Alinco DR-635.  This cost is probably less than the sum of most midrange dual band HTs plus a separate RF amplifier like that noted above. With many of the inexpensive Chinese HTs on the market, the combined cost is perhaps somewhat less than the mobile transceiver. The value, convenience, and typical use should be considered in determining which option is best for the individual user, but the more common solution among the two options described here is the mobile transceiver in lieu of HT + amplifier for most hams.

The answer to Technician question T7A10, “What device increases the low-power output from a handheld transceiver? is B: An RF power amplifier.

Related Questions:   T7A02, T8A02, T8A04, T9A04, T9A07