CONFIDENTIAL – LIMITED DISCLOSURE ADDENDUM TO EXISTING PCB DESIGN BRIEF 433.92 MHz ANTENNA REQUIREMENT This document is an additional requirement to the previously issued XIAO ESP32C3 Carrier PCB hardware design brief. 1. DEFAULT ANTENNA IMPLEMENTATION --------------------------------- Use a PCB-integrated 433.92 MHz antenna as the default receive antenna for the removable SYN480R V199 receiver module, provided that this can be implemented without materially increasing the overall PCB dimensions. The preferred implementation is a compact proven PCB antenna geometry suitable for 433.92 MHz, such as a meandered monopole or equivalent low-cost PCB-integrated antenna. The antenna is receive-only and is used by the SYN480R receiver path. 2. ANTENNA LOCATION ------------------- Place the 433.92 MHz PCB antenna close to a PCB edge. Keep it as far as practical from: - the XIAO ESP32C3 2.4 GHz antenna, - digital switching circuitry, - buzzer circuitry, - IR driver/current paths, - battery hardware, - spring contacts, - large metallic connectors or other conductive objects. Where practical, place the 433.92 MHz antenna and the XIAO ESP32C3 2.4 GHz antenna at opposite sides/edges of the PCB. 3. ANTENNA KEEPOUT ------------------ Provide the required copper/component keepout area around and underneath the 433.92 MHz PCB antenna according to the selected antenna geometry and RF design requirements. Do not route: - signal traces, - power traces, - GND copper, - switching-current traces, - vias, - components inside the antenna keepout region unless specifically required by the validated antenna design. Clearly identify the antenna keepout in the PCB design notes. 4. RF FEED ---------- Connect the SYN480R ANT node to the antenna through a short and direct RF feed path. Requirements: - Keep the RF feed as short as practical. - Avoid unnecessary vias. - Avoid unnecessary bends. - Keep noisy/high-current traces away from the RF feed. - Do not route the RF feed through switching-current areas. 5. EXTERNAL SPRING/HELICAL ANTENNA BACKUP ----------------------------------------- Provide a DNP footprint/pad for an alternative external 433.92 MHz spring/helical antenna. This backup antenna must not be populated by default. The PCB must allow the designer/assembler to select either: A. the PCB-integrated antenna, or B. the external spring/helical antenna. Do not connect both antennas simultaneously in normal operation. 6. 0-OHM ANTENNA SELECTION LINK ------------------------------- Provide a 0-ohm selection/link arrangement so that the active antenna path can be changed without redesigning the PCB. Default production configuration: - PCB-integrated antenna selected. - External spring/helical antenna path disabled / DNP. The 0-ohm link arrangement must allow the PCB antenna to be isolated if the external antenna is later required. 7. OPTIONAL RF MATCHING NETWORK ------------------------------- Provide a compact optional PI matching-network footprint between the SYN480R ANT node and the antenna feed. The matching network must be DNP by default unless RF measurements show that matching components are required. Do not guess matching component values. Matching values, if required, must be selected only after RF measurement/tuning on the real PCB and preferably with the final enclosure. 8. RF TEST / TUNING PROVISION ----------------------------- If PCB space allows, provide either: - an accessible RF test point, or - an optional DNP RF test-connector footprint for RF tuning and pre-compliance measurement. The test provision must not materially disturb the RF path when unused. 9. SILKSCREEN / IDENTIFICATION ------------------------------ Clearly identify: - RF 433 ANT - external spring/helical antenna backup pad - 0-ohm selection link(s) - optional matching-network components - Pin 1 / orientation where applicable Use normal reference designators for all related parts. 10. CE / RED PRE-COMPLIANCE --------------------------- The antenna layout must support the previously specified CE / EU RED design-for-compliance requirement. The designer must: - review antenna placement and separation, - maintain appropriate RF keepout, - minimize RF interaction with the XIAO 2.4 GHz antenna, - avoid noisy trace routing near the antenna, - document the selected PCB antenna geometry, - provide the antenna type/reference information, - document any matching/tuning components used, - support reasonable layout or matching changes if prototype/pre-compliance testing identifies an RF/EMC issue. 11. COST OBJECTIVE ------------------ The PCB-integrated antenna is the preferred default because it avoids the cost of an additional antenna component and assembly operation. However, the PCB antenna must not be used if it causes a significant increase in PCB dimensions or materially reduces RF reliability. The final design must prioritize: 1. reliable RF reception, 2. CE/RED pre-compliance readiness, 3. low production cost, 4. compact PCB dimensions. END OF ADDENDUM
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