2-35
Figure 2-24.—Single-ended crystal mixer.
One type of mixer which cancels local oscillator noise is the BALANCED, OR HYBRID, MIXER
(sometimes called the MAGIC T). Figure 2-25 shows this type of mixer. In hybrid mixers, crystals are
inserted directly into the waveguide. The crystals are located one-quarter wavelength from their
respective short-circuited waveguide ends (a point of maximum voltage along a tuned line). The crystals
are also connected to a balanced transformer, the secondary of which is tuned to the desired IF. The local
oscillator signal is introduced into the waveguide local oscillator arm and distributes itself as shown in
view A of figure 2-26. Observe that the local oscillator signal is in phase across the crystals. In view B the
echo signal is introduced into the echo signal arm of the waveguide and is out of phase across the crystals.
The resulting fields are shown in view C.
