Although wideband receiver front ends are in increasing use, they cannot handle situations with very strong off-channel signals. Passive tuned circuit filters are still needed to protect against cross-modulation, IM, damage, and other interference effects. The trend is toward separately packaged preselector filter units using sophisticated tuning and control methods. Selectivity, noise figure degradation, and maximum interference voltage are important constraints. It is possible to design filters with an optimal trade-off of these parameters for given component limitations. With some forethought in the filter design, several preselectors can be driven by the same antenna in a multicoupling configuration. The same filters or similar circuits can be employed as postselectors to filter the transmitter signal before final power amplification, thus reducing its out-of-band noise and spurious emissions that could interfere with nearby receivers.

Chapter Contents:

• 9.1 Purpose and General Description
• 9.2 Design Considerations for Preselectors
• 9.3 Filter Design
• 9.4 Design Examples
• 9.5 Implementation Considerations
• 9.6 Computer Aids
• 9.7 Multicoupling
• References

Inspec keywords: passive filters; interference suppression

Other keywords: damage effects; filter design; IM; wideband receiver front ends; multicoupling configuration; power amplification; maximum interference voltage; interference effects; tuning methods; noise figure degradation; out-of-band noise reduction; passive tuned circuit filters; selectivity; cross-modulation; spurious emissions reduction; preselectors filter units; postselectors; control methods

Subjects: Electromagnetic compatibility and interference; Passive filters and other passive networks