The Advance Type B4 Signal Generator is available in two versions, the B4A and B4B, each providing a wide frequency range with accurate frequency and output voltage calibration. The frequency ranges are 100 kc/s to 80 Mc/s on B4A, and 30 kc/s to 30 Mc/s on B4B. The accuracy of frequency calibration is ± 1% A linear scale and vernier are provided to give very close resetting accuracy. Due to the use of a crystal voltmeter followed by our type A.38 high frequency resistive attenuator, the output is measured to ± (1 dB + 2% F.S.D.). The signal can be modulated internally at 400 c/s from 0 to 80%. External modulation, also O to 80%, may be applied up to 30 kc/s into the B4A and up to 10 kc/s into the B4B. Both internal and external modulation depths are monitored.