A Twin-tone/Multitone IM Signal Source
This page will describe the design of a twin-tone high-frequency IM source that can be used to perform CCIF 19 kHz + 20 kHz IM distortion tests. The unit can also generate the three-tone MIM test signal (9 kHz + 10.05 kHz + 20 kHz).
The source employs two or three simple fixed-frequency Wein bridge oscillators, each of which comprises little more than a dual JFET op amp and a discrete JFET for agc. The outputs of the oscillators are combined in the an inverting mixer by a very low distortion op amp, so that IM products in the resulting test signal depend only on the low-distortion performance of the mixer and not the individual oscillators.
This page will be completed soon. Stay tuned.