mixers that operate with both even and odd harmonics have one diode,
require a DC
return path for the diode current. This DC return path follows the IF path in the diplexer, and the device attached to
the IF port of the diplexer must have some provision for the diode current. This may take the form of the 50 ohm (DC)
input impedance of the IF amplifier, an inductor to ground or a diode bias circuit. Mixer conversion loss is dependent
upon frequency, harmonic number and applied LO power as well as diode current. Many spectrum analyzers have a
mixer bias provision, and this bias can be used to peak the output from the mixer to optimize performance.
Mixers designed to operate on even LO harmonics only or odd LO harmonics only have two diodes in an anti-parallel
configuration and do not require bias for normal operation. Bias can be used, however, to make an "even only" mixer
operate with odd LO harmonics or an "odd only" mixer operate with even LO harmonics.