Video Transmission RF Board PCBA

High-Linearity OFDM Video Transmitter —<3% evm="">

Product Overview

The Video Transmission RF Board is a high-performance RF front-end PCBA purpose-built by Superb Automation for the challenging task of transmitting high-bandwidth digital video over wireless channels from UAVs to ground receivers. Unlike voice or telemetry radios that operate with narrow bandwidths and simple modulation, video transmission demands wideband RF circuitry capable of handling OFDM signals with 64-QAM or 256-QAM subcarrier modulation, peak-to-average power ratios exceeding 10 dB, and occupied bandwidths up to 20 MHz. This board delivers on all these requirements through a carefully designed signal chain optimized for linearity, spectral purity, and thermal stability. All fabrication meets IPC-6012 Class 3 for high-frequency RF substrates.

The PCBA uses a 4-layer Rogers RO4350B substrate with all RF traces implemented as grounded coplanar waveguides at 50 Ω. The transmitter chain features a Skyworks SE5004L power amplifier delivering +26 dBm linear output power with an error vector magnitude (EVM) below 3% at 64-QAM — a critical metric for maintaining high data throughput without packet errors. A digital pre-distortion (DPD) feedback path samples the PA output through a directional coupler and provides correction data to the baseband processor, enabling the PA to operate closer to its compression point without degrading modulation accuracy. The board covers the 2.4 GHz and 5.8 GHz ISM bands with band-switching achieved through PIN-diode-switched SAW filter banks providing >45 dB of adjacent channel rejection. DO-160 Section 21 compliance is verified for spectral mask and spurious emissions.

Key Specifications

OFDM Linearity Requirements

OFDM modulation with high-order QAM constellations demands exceptional PA linearity to prevent spectral regrowth and constellation distortion. The board's PA is backed off from its P1dB compression point by 6 dB in linear mode, achieving an ACPR of >45 dBc. The DPD feedback loop samples the PA output, compares it to the ideal baseband waveform, and applies inverse predistortion coefficients updated every 100 ms to track thermal drift. This closed-loop correction allows the PA to operate 2–3 dB closer to compression than open-loop designs, improving DC-to-RF efficiency by approximately 15%. The Rogers RO4350B substrate's low Dk variation (±0.05) across the operating band ensures consistent impedance matching regardless of channel selection.

Test Strategy

Every assembled board undergoes full modulation analysis using a vector signal analyzer: EVM is measured across all subcarriers at maximum bandwidth, spectral mask compliance is verified per regulatory requirements, and ACPR is measured at ±20 MHz offset. The DPD loop is tested by injecting a stepped-power ramp and verifying EVM remains below 3% across the entire output power range. Band switching is verified for insertion loss (<1.5 db="">

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