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A diode multiplier can be made to produce considerably more harmonic output if it is biased, as shown in Fig. 1. This is particularly effective when the order of frequency multiplication required is high, as it frequently is in converters for 220 Mc. and higher bands. For example, the 220-Mc. converter in the Handbook requires quadrupling from 51.5 to 206 Mc.

Fig 1
Fig. 1. (A) Typical diode multiplier circuit. (B) Modified multiplier circuit for increased harmonic output.
C1-Button mica, standoff or feedthrough ceramic.
L1-C2-Tuned circuit, set to desired harmonic.
R1-Bias resistor, value determined experimentally.

Particular attention should be paid to the bypass capacitor Cl; preferably it should be a button mica, standoff or feedthrough ceramic type. The tuned circuit, L1 C2, should have high Q at the desired frequency to discriminate against unwanted multiples of the driving frequency as much as possible.

Frank Greene, K5IQL.

(Several factors determine whether biasing a multiplier diode will increase the level of a particular harmonic. Important considerations include the amount of drive available, the value of the bias resistor, the order of frequency multiplication, the type of mixer and the method of mixer injection. The usefulness of diode multiplier bias in any circuit is best determined empirically. - Editor.)