Determining Antenna Separation Requirements for Co-Located Transmitters
Minimum antenna separation depends on transmitter power, receiver blocking thresholds, intermodulation mixing products, and regulatory simultaneous exposure ratios.
Out of Band Noise Floor
Meaning
Radio receivers are susceptible to desensitization when strong signals or broadband noise generated outside the operating channel leak into the sensitive input stages. The out of band noise floor represents the level of residual noise present in these non-operating frequency bands during transmission. Maintaining a low noise level in these regions is necessary to prevent interference with adjacent communications.
Spectral Interference
Transmitter architectures always generate some broad thermal noise that spills over into neighboring channels. The out of band noise floor is a critical metric because a high noise level can drown out weak signals on other devices operating nearby. Designers must budget this emission level when integrating the transceiver module onto a multi-radio system board.
Filtering Efficiency
Bandpass and bandreject filters are placed after the power amplifier to suppress these unwanted out of band emissions. Without adequate filtering, the out of band noise floor rises, causing the system to fail regulatory spectral mask requirements. The insertion loss of these filters must be balanced against the needed noise suppression to maintain output efficiency.
High-performance ceramic filters are typically integrated into the antenna path to achieve the sharp rolloff required for dense frequency environments.
System Verification
Spectrum analyzers measure this parameter during formal transceiver certification. Tests run while the module transmits at full power to verify that noise in the adjacent bands remains below the limits. This step protects public airways.