wave oscillator, uses an electron beam longitudinally focused by a magnetic field, and a slow-wave circuit interacting with the beam. A collector collects the beam at the end of the tube. O-BWO spectral purity and noise The BWO is a voltage tunable oscillator, whose voltage tuning rate is directly related to the propagation characteristics of the circuit. The oscillation starts at a frequency where the wave propagating on the circuit is synchronous with the slow space charge wave of the beam. Inherently the BWO is more sensitive than other oscillators to external fluctuations. Nevertheless, its ability to be phase- or frequency-locked has been demonstrated, leading to successful operation as a heterodyne local oscillator. Frequency stability The frequency–voltage sensitivity, is given by the relation f/f = 1/2 [1/(1 + |vΦ/vg|)] (V0/V0) The oscillation frequency is also sensitive to the beam current (called "frequency pushing"). The current fluctuations at low frequencies are mainly due to the anode voltage supply, and the sensitivity to the anode voltage is given by f/f = 3/4 [ωq/ω/(1 + |vΦ/vg|)] (Va/Va) This sensitivity as compared to the cathode voltage sensitivity, is reduced by the ratio ωq/ω, where ωq is the angular plasma frequency; this ratio is of the order of a few times 10−2. Noise Measurements on submillimeter-wave BWO's (de Graauw et al., 1978) have shown that a signal-to-noise ratio of 120 dB per MHz could be expected in this wavelength range. In heterodyne detection using a BWO as a local oscillator, this figure corresponds to a noise temperature added by the oscillator of only 1000–3000 K. Notes References Johnson, H. R. (1955). Backward-wave oscillators. Proceedings of the IRE, 43(6), 684–697. Ramo S., Whinnery J. R., Van Duzer T. - Fields and Waves in Communication Electronics (3rd ed.1994) John Wiley & Sons Kantorowicz G., Palluel P. - Backward Wave Oscillators, in Infrared and Millimeter Waves, Vol 1, Chap. 4, K. Button ed., Academic Press 1979 de Graauw Th., Anderegg M., Fitton B., Bonnefoy R., Gustincic J. J. - 3rd Int. Conf. Submm. Waves, Guilford University of Surrey (1978) Convert G., Yeou T., in Millimeter and Submillimeter Waves, Chap. 4, (1964) Illife Books, London External links Virtual Valve Museum Thomson CSF CV6124 (Wayback Machine) Microwave technology Terahertz technology Vacuum tubes