SRRC Filing Timelines for a Product Entering China
SRRC radio type approval in China takes 8 to 16 weeks, requiring local agent representation, strict customs sample clearing, and accredited domestic lab scans.
Co-Located Transmitter Intermodulation
Meaning
Harmonic interference happens when multiple nearby antennas radiate simultaneous signals that mix inside non-linear circuit elements to produce new unwanted frequencies. Detecting co-located transmitter intermodulation identifies signal leakage that falls into active receiving bands of the same device. This measurement prevents self-interference in complex connected devices where cellular antennas sit millimeters away from wireless local area network chips.
The resulting phantom signals typically appear at predictable mathematical combinations of the primary frequencies.
Signal Interaction
Mixing occurs when the radiated energy of one transmitter reaches the final amplifier stage of a nearby radio. The co-located transmitter intermodulation levels increase when physical isolation between radiators is low or when power amplifiers lack sufficient output filtering. Third-order products are the most concerning as they reside mathematically close to the original bandwidth.
These peaks introduce a rising noise floor that blinds the device to weak incoming signals.
Hardware Design
Designers insert high-rejection bandpass filters to suppress the transfer of energy between antennas. Evaluating co-located transmitter intermodulation requires testing in an electromagnetic silence chamber with all radios active at maximum gain. If a board layout places the primary transmit path directly over a receiver trace, the resulting coupling facilitates the intermodulation effect.
Inductors and capacitors near the feed points help manage internal reflections.
Compliance Verification
Regulatory testing evaluates these unwanted emissions to ensure they do not exceed prescribed spurious limits at the chassis boundary. A passing result for co-located transmitter intermodulation proves the design effectively separates distinct communication channels. Measurement tools isolate the spectral components during a simultaneous dual-band data transfer.
If thresholds are exceeded, the device fails to gain the necessary market entry certificate.