Wide-Range Double-Heterodyne Spectrum Analyzers

Spectrum analyzers using double-heterodyne converter units can cover very wide frequency bands. A typical instrument described in this paper covers the range from 10 to 3000 megacycles. The signal frequency is changed to 24,600 megacycles by a crystal mixer and a special beating oscillator. A band-pass filter network rejects undesired frequencies and passes the output of the first mixer to a second crystal, where the frequency is reduced to 115 megacycles. A narrow-band amplifier increases the level at this frequency and drives a cathode-ray presentation unit. Also mentioned are two other analyzers using production oscillators and covering smaller ranges. The succeeding sections of the paper discuss qualitatively the following points: frequency stability, losses and noise figure, and suppression of spurious responses.