The KPA3A option consists of three sub assemblies: the KPA3A power amplifier, a fan panel to provide cooling, and the KPAIO3A interface module.
The KPAIO3A acts as an interface between the RF board and the KPA3A power amplifier. It includes a relay that allows the KPA3A to be bypassed when it is not needed during low power operation. The cooling fans are also controlled by circuitry on the KPAIO3A. There are four fan speeds, plus OFF, selected automatically based on measurement of the KPA3A heat sink temperature.
KPA3A Fan Panel
Two fans are mounted on this panel, along with a circuit breaker to protect the KPA3A from accidental short circuits. The fan panel is connected to the KPAIO3A fan connectors and to the heavy 12-volt connections of the KPA3A module.
KPA3A Power Amplifier
The KPA3A Power Amplifier consists of two RF power transistors operating as a broadband push-pull amplifier; a PIN diode TR switch; and associated bias and control circuitry. The KPA3A provides the necessary gain to increase the power output of the K3S or K3 from 10 watts to 100 watts from 1.8 MHz and 54 MHz. A heat sink is provided that, together with the cooling fans, provides the necessary cooling to maintain the operating temperature of the output transistors at a safe level.
The KPA3A is mounted in the K3S/K3 with the circuit side of the board down so that only the heat sink is visible after removing the top cover. Each KP