How do you know how clean your HF SSB transmitter or amplifier is? One of the most important performance measurements is Transmit Intermodulation Distortion (IMD).
Elecraft's new 2T-gen is a 2-tone test oscillator that has been designed to provide a standard 2-tone (700 and 1900 Hz) audio source for testing of SSB transceivers and linear amplifiers. This type of testing is almost universally used as a measure of transmitter linearity for amateur radio equipment. (Linearity impacts both SSB fidelity and the amount of SSB splatter that causes adjacent channel interference.) Results of 2-tone IMD tests can be found in every ARRL review of new transceivers and power amplifiers.
The 2T-gen is battery operated and provides sufficient output level (0-200 mV) to be connected directly to the microphone connector of almost any transceiver. Transmitter linearity can be determined by observing the 2-tone envelope on an oscilloscope or station monitor. For more exacting IMD measurements the output can be measured using a spectrum analyzer.
For the 2T-gen, F1 is 700 Hz and F2 is 1900 Hz, which results in a 3rd order product of 3100 Hz and a 5th order product of 4300 Hz. The amplitude of these undesired outputs is usually increased as the transmitter output is increased, and is caused by various transmitter amplifier stages beginning to operate in compression.
Like our other low-cost mini-modules, the 2T-gen is quite small: the PC board is just 2.5"W by 3.5"L. Rubber feet are also included so the unit can be used on the workbench.