Timebase Calibration

The DDS RF Signal generator described in the October 2003 issue of Elektor Electronics has an internal 10 MHz quartz crystal oscillator for the AD9851 DDS chip. Obviously, the output frequencies supplied by the generator are only correct if the quartz crystal is adjusted to exactly 10.000 MHz using trimmer C22. For many applications like repair work on 445 kHz or 10.7 MHz IF amplifiers, the frequency of the signal supplied by the instrument is not terribly important. However, ‘netting’ narrow band FM (NBFM) equipment like a 6-m (50 MHz) amateur radio transceiver does require a frequency-accurate test source. After all, if you adjust the transceiver with the aid of a signal generator, any error in the frequency supplied by the latter is copied by the local oscillator(s) of the 50-MHz receiver.