Digital Synchronizer TF 217ÖB (Fig. 1.1) is a self contained instrument designed expressly for use with the TF 2002 s e r ie s of signal g en e ra to rs. The (synchronizer is constructed to be easily fitted to the signal g en e rato r and when the instruments a re used together, the combination can be classified as an accurate and stable phase locked frequency synthesizer covering a range 32 kHz to 88 MHz when used with signal generator TF 2002B or 100 kHz to 72 MHz when used with TF 2002 or TF 2002AS. The setting up procedure is extremely simple and calls only for the positioning of the TF 2170B frequency switches and the tuning of the signal generator to obtain a 'locked on* condition which holds the frequency of the signal generator to within 1 p. p. m. of the frequency indicated by the synchronizer switches for ambient temperatures from +10 ° to 35 °C. Used together, the combination provides an r. f. source with many applications. Solid state circuits are employed throughout to ensure long term reliability and the design provides for easy access to a ll components for servicing. If desired, the signal generator can be used independently without disconnection, by operating a switch located on the front panel of TF 2170B.