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Ten-Tec 418 Power Amplifier | Radioaficion Ham Radio

Ten-Tec 418 Power Amplifier


Ten-Tec Model 418 100W RF External Power Amplifier

Ten-Tec Model 418 100W RF External Power Amplifier

Operating Frequency: 1.8 - 54 MHz (Amateur Bands Only)

Power Source: External DC Power Supply +13.8V @ 17A (typical)

The amplifier operates only in the amateur radio bands below 30 MHz and also in the 6 meter amateur band (50-54 MHz). The amplifier is NOT capable of operation on any frequency outside of the amateur bands including 26-28 MHz and also will NOT operate above 54 MHz.

The amplifier typically requires 4-6 Watts of drive to obtain full output power depending upon which transmit band it is on.

The gain of the amplifier is less than 15dB on all bands under all conditions.

In off or standby positions the amplifier does NOT amplify. The exciter energy is simply passed on to the antenna at the same level in which it entered the amplifier. The spurious emissions of the transceiver remain unaffected.


Ten-Tec Model 418 100W RF External Power Amplifier

Ten-Tec Model 418 100W RF External Power Amplifier

Theory of Operation

With the Model 418, Ten-Tec has created a 100-watt solid state silicon MOSFET amplifier combining automatic and manual control for ease of operation in the 160 through 6 meter ham band.

Refer to the Block Diagram for the following discussion.

Ten-Tec Model 418 block diagram

Receive signals are routed through the antenna connector to the antenna relays on to the T/R relay switching on the Lowpass Filter Board. From here the receive signals are passed on to the Radio connector. Transmit signals are applied at the Radio connector and routed to the T/R relay switching on the Lowpass Filter Board and then on to the input attenuator, input power bridge and frequency counter. The transmit signal is then applied to the 100-watt MOSFET amplifier and passed back to a lowpass filter to be applied to the correct filter and then on to the antenna relays, and finally, to the antenna connector.

Ten-Tec Model 418 100W RF External Power Amplifier

The PIC processor in the CPU module executes the firmware to perform certain functions. Those functions include:

1. checking input power and frequency

2. enabling bias to the MOSFET amplifier

3. checking SWR

4. checking current

5. checking output power

6. checking temperature

The PIC performs these functions based on input from the front panel buttons, key in jack or data from the ACC 1 connector.

Cooling is achieved with the two internal fans that are also controlled by the CPU.

Connection to Antenna & Power Supply

The 418 is designed for use with any antenna system providing 50 Ohm resistive impedance at the desired operating frequency. Every effort should be made to ensure the impedance of the antenna system is as close as possible to the specified 50-Ohm value.

The 418 requires a source of well-filtered and regulated DC voltage. The supply voltage on the 418 is 13.8 Vdc nominal +/- 15% to allow for mobile and battery operation. The voltage source must be capable of supplying 23 amperes continuous duty.

We recommend using the included DC power cable (P/N 46214). Use of #12 stranded wire is recommended for mobile and in home use to accommodate the required current demand during transmit.

Note: Always enable the power source first and then the amplifier. If a generator or battery connected to a charger is used to supply the DC source, always turn off the amplifier before starting or shutting off the DC source equipment. These recharging devices often generate large voltage spikes that can damage the amplifier.

Ten-Tec Model 418 100W RF External Power Amplifier

A word about grounding

A good ground system is essential for optimum operation of any HF transmitter. The best solution is to connect all the station equipment to a single ground connection. Refer to Local and National Electrical Codes before making any connections with the 418. Another source of information on grounding can be found in the ARRL Handbook.

A good ground system can contribute to the station efficiency in a number of ways including minimizing the possibility of electrical shock, and minimizing RF currents flowing on the shield of the coax cable causing interference to electrical equipment and transceiver accessories.

It is critical that the power supply, the 418, and other equipment in the station be properly grounded to an Earth ground. Improper grounding can lead to various issues, including RFI, ground loops, or even death. Therefore it is extremely important to refer to the Local and National Electrical Codes and ARRL Handbook with regards to grounding.

TEN-TEC 418 Resources:




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