Crystal Checker for Balanced Mixers

To achieve optimum performance from a microwave receiver that uses a balanced crystal mixer, matched pairs of crystals should be used. However depending on the reason for choosing the balanced mixer for a particular receiver, the crystal characteristics that should be matched and the degree of balance that is required vary considerably. The three principal reasons for using balanced mixers are: 1. To minimize noise figure by suppressing local-oscillator noise. 2. To suppress local-oscillator power radiation. 3. To reduce receiver sensitivity to certain spurious responses. For radar receivers, the first reason is the only important one, and fortunately it places the least stringent requirement on the degree of balance.