HF amplifier RM Italy MLA 400

Practical benefits of the RM Italy MLA 400 HF amplifier

The RM Italy MLA 400 is a transistor linear HF amplifier operating in the 1.8–30 MHz range, designed primarily for transceivers with an output of around 100 W, but it also works equally well with lower-power stations capable of delivering excitation power from 1 to 35 W. The practical meaning of such an addition is most visible when operating on crowded HF bands, in contests, during DX contacts or when working from the field, where increasing the output power from the standard 100 W to the declared up to 400 W of average power significantly improves the chance of a successful connection, especially in poor propagation.

Power supply from 13.6 V DC allows the amplifier to be used not only in a home station, but also in a mobile or portable installation - the manufacturer directly declares its suitability for both types of use. Automatic selection of the low-pass filter according to the operating band and microprocessor-controlled protection functions (against wake-up, high PSV, overheating and out-of-band operation) reduce the risk of damage to the output transistors during normal operation.

Features and technical parameters of RM Italy MLA 400

The output stage consists of four RF power transistors (RM1607 / 2SC2879 / MRF421) arranged in two parallel push-pull pairs operating in class AB, which ensures the linear waveform of the output signal necessary for SSB, AM and other modes sensitive to linearity. Harmonic components are filtered by a set of six low-pass filters with cutoff frequencies of 3, 4, 5, 8, 15, 22 and 31 MHz; the filter for the current operating band is selected automatically according to the sensed excitation frequency, or it can be selected manually from the front panel. The entire operation, including protection functions, is controlled by a built-in microprocessor.

Technical specification

Front and rear panel description

The amplifier's controls and connectors are divided between the front panel, where the controls and indications are located, and the rear panel, where all connections to the transceiver, antenna, and power supply are made.

Front panel

Rear panel

Amplifier connection and operation

The connection is based on a simple sequence of steps. The RTX input is connected to the transceiver output with a short 50 Ω cable, the ANT output can be connected to an external power meter or automatic antenna tuner (ATU), and then to the antenna. The power cables should be connected to a source or battery with a voltage of 13.6 V (±1 V) capable of delivering at least 70 A. The wires to the source should have a diameter of at least 6 mm² and be as short as possible to minimize voltage drop; for mobile installations, they should not exceed 3 m in length and should be connected directly to the car battery, ideally with an additional fuse in the supply.

Connecting the PTT to the amplifier is optional - the device includes an RF scanning function (similar to VOX), which automatically switches it to transmission when an excitation signal is detected at the input. Before the first power-on, the transceiver output power must be reduced to a value of up to 35 W (around 10 W is recommended) and this adjustment must be made with the amplifier turned off. The filter for the current band can be set manually, or the amplifier will select it automatically when transmitting for the first time.

The amplifier must not be used while the antenna is being tuned by a manual or automatic antenna tuner. After the antenna has been tuned, the automatic ATU must be switched to standby mode so that another tuning cycle does not start while broadcasting with the amplifier active.

After turning on the amplifier and starting to transmit, it is necessary to verify that the antenna PSV remains within an acceptable range - a value of around 1.1:1 is ideal, up to 2.0:1 is acceptable, and from approximately 2.5:1 the protection is activated. When it is activated (with the exception of the thermal protection, which resets itself after cooling down), the amplifier must be turned off and on again to restore normal operation.

When transmitting in high duty cycle modes (FM, data traffic), the manufacturer recommends not to exceed continuous transmission for more than one to two minutes to prevent overheating of the output transistors; for SSB and CW, where the power is intermittent or peaks only briefly, the thermal load is significantly lower. According to the manufacturer, the difference between the 35 W excitation power and the 400 W output represents an increase of approximately 10.6 dB, which corresponds to almost two S-points on the receiving side - an improvement that would be difficult to achieve for most stations with the antenna alone.

Where to buy and price

The RM Italy MLA 400 is distributed by several European amateur radio dealers, prices vary by country, current promotions and shipping costs. Directly from the manufacturer RM Italy, the amplifier is listed in the product catalog, including a technical sheet and manual, but the sale itself is carried out through a network of authorized dealers.

When ordering from abroad, you should consider shipping costs and possibly customs and tax fees, which vary depending on the seller and the country of delivery; some sellers (such as Moonraker) include these fees for EU countries directly in the listed price.