TRANSVERTER INTERFACING
2 Meter IF Load/Attenuator
W3KM, November 1992
Transverter transmit mixers require 1 to 10 mW of IF power. When the low-level stage of a 10-watt transceiver can not be tapped into, a suitable 50-ohm load and attenuator is required.
A flanged microstrip mounted 50-ohm load of 10-30 watts is used to dissipate the power. A small value variable capacitor couples off a small amount of power. A fixed value attenuator follows to provide the required attenuation and 50 ohm match to drive the transmit mixer. The circuit shown will provide >35 dB of attenuation at 144 MHz. Additional attenuation can be accomplished with a 100 ohm pot or a chip resistor attenuator at the mixer port.
This circuit should be built into a metal enclosure. Even so, it is still possible to work a strong station on the IF frequency when running 10 watts. Good coaxial relays or a high isolation Pin diode switch must be used. Additionally, switching off your 2-meter station GaAsFET preamp during transverter operation will also help considerably.