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We describe how to perform signal averaging using a multichannel analyzer without internal modification. It thus becomes possible to average signals with the aid of “borrowed” equipment. Required equipment, in addition to a multichannel analyzer, consists of approximately $100 worth of transistor circuitry and a voltage to frequency converter.

Broadband microwave radiation in the X and KA bands was observed from a non-neutral electron layer prepared by passing a 2.5-MeV straight hollow electron beam through a narrow magnetic cusp. The mean beam radius shrank from 6 to 4.5 cm and the beam radial width increased from less than 1 to 2.7 cm in the postcusp e-layer drift region. When the beam was passed through a thin scattering foil prior to cusp transmission, the observed radiation decreased by two orders of magnitude and the beam width and radius remained at values consistent with single-particle calculations. Results are discussed in terms of the negative-mass instability.

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