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RF Guru

RX Frontend Protector – Galvanic Isolator & RF Limiter (0.5MHz - 125 MHz)

RX Frontend Protector – Galvanic Isolator & RF Limiter (0.5MHz - 125 MHz)

€119,00 EUR
€119,00 EUR
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Handmade in Belgium — Small-batch assembly and individual testing. Please allow 1–2 weeks for fulfilment depending on order volume.

The RX Frontend Protector – Galvanic Isolator & RF Limiter is a passive, wideband in-line protection module designed to safeguard sensitive HF/VHF receiver and SDR front ends against ESD, static buildup, and excessive RF levels caused by nearby transmitters.

Optimized for HF reception (0.5–125 MHz), this module combines multi-stage ESD and surge protection, a wideband MMIC RF limiter, and a 1:1 RF transformer isolator. When installed directly at the receiver input, it helps prevent permanent damage, reduces front-end overload, and improves immunity to common-mode noise pickup.

What This Module Does in Practice

  • Protects receiver inputs from ESD, static discharge, and accidental high RF exposure.
  • Limits strong RF signals so coupled TX energy is capped to receiver-safe levels.
  • Provides galvanic isolation to break ground loops and suppress shield-borne noise.
  • Improves receive SNR by reducing common-mode noise that often dominates modern HF installations.

ESD and Static Discharge Protection

The front-end protection network safely diverts fast, high-voltage transients away from the receiver input before they can reach sensitive circuitry:

  • Gas discharge tube surge arrestor — conducts high-energy ESD and surge events to ground once its sparkover voltage is exceeded, while remaining effectively invisible to RF during normal operation.
  • High-value static bleed path (1.2 MΩ) — prevents charge accumulation on the antenna or coax.
  • Low-capacitance ESD clamp array — provides fast secondary clamping for residual ESD energy and sharp voltage spikes.

Outcome: ESD events are dissipated before reaching the limiter stage or receiver input.

RF Limiting for Strong Signal Protection

A wideband MMIC limiter follows the ESD stage and acts as the primary RF amplitude protection element. It is designed to tolerate high incident RF levels caused by near-field coupling from nearby transmit antennas.

  • Handles high RF input levels without damage.
  • Clamps excessive RF so the receiver is not driven into destructive or severe over-range conditions.
  • Design target: up to +32 dBm input limited to ≤ +8 dBm at the output.

The limits stated in the specifications are conservative. In practical testing, the device was exposed to 5 W CW RF input and consistently delivered approximately +8 dBm PEP at the receiver-side output.

Galvanic Isolation and Common-Mode Noise Rejection

A 1:1 RF transformer provides galvanic isolation between antenna-side and receiver-side grounds:

  • No DC continuity between antenna and receiver.
  • Strong suppression of common-mode currents on coax shields.
  • Reduced RF stray pickup entering the receiver chassis.

In real installations, the noise reduction achieved by this isolation typically results in a net SNR improvement that exceeds the small insertion loss of the device.

Recommended Placement

  • Install directly at the receiver input for maximum protection and noise reduction.
  • Avoid unintentionally bonding antenna-side and receiver-side grounds together.
  • Keep isolation intact unless your mechanical design explicitly accounts for it.

Integration Notes

  • Impedance: Designed for standard 50 Ω systems.
  • DC blocking: No DC pass-through due to the transformer. If using bias-T powered active antennas, inject DC on the antenna side.
  • Not a T/R switch: Intended for incidental RF coupling and transient protection only.

Technical Specifications

Parameter Specification
HF optimization range 0.5 – 125 MHz
Wideband operating range 1 – 400 MHz
Optional Band Pass Filter operating range 1.7 – 30 MHz
Optional Low Pass Filter operating range 0 – 30 MHz
Insertion loss < 1 dB
VSWR < 1.6
Common-mode rejection ±10 dB on HF, >30 dB on 160 m / 80 m / 40 m
Output limiting level Max +8 dBm
Limiter input handling Up to +32 dBm (conservative rating)

S-Parameter Measurements

S11 (Return Loss)

RX Frontend Protector S11 measurement

S21 (Insertion Loss)

RX Frontend Protector S21 measurement

Live RF Limiting Test

Mini-FAQ

  • Will it affect weak signals? — No. Insertion loss is <1 dB, and the limiter only acts on strong RF. In practice, the galvanic isolation and common-mode noise reduction often provide a net SNR improvement compared to a direct connection.
  • Is this an active device? — No. It is fully passive and requires no power.
  • Can it replace a T/R switch? — No. It is not intended for intentional transmit power.
  • Is DC passed through? — No. The transformer provides full DC isolation.
  • Where should it be installed? — Directly at the receiver input for best results.
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