ELT GNSS Receiver EMI Protection Circuit

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Solution Overview

Problem

Aircraft ELTs with GNSS receivers are vulnerable to damage from unintentional RF radiators and electromagnetic interference (EMI) due to the presence of various communication devices on board, which can degrade their performance and sensitivity during normal flight and emergency situations.

Innovation Solution

Incorporating a 406 MHz blanking switch, GNSS high-pass filter, and surface acoustic wave (SAW) filters into the ELT's triplexer-EMI protection filter circuitry connected to the antenna, providing isolation and filtering to protect the GNSS receiver from high-power RF transmissions and EMI, including those from Iridium, KU, KA, and other band transmitters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If various communication devices and RF transmitters are installed on aircraft, then communication and navigation capabilities are improved, but unintentional RF radiators and EMI damage the GNSS receiver

Engineering Contradiction:

Improvecommunication capabilitiesVSAvoidRF interference and EMI

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces a triplexer-EMI protection filter circuit as an intermediary component between the antenna and the GNSS receiver. This filter circuit selectively passes desired frequency bands while blocking harmful RF frequencies and EMI from various aircraft communication devices, thus protecting the GNSS receiver without compromising communication capabilities

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent segments the RF signal processing by using multiple specialized filters (triplexer, EMI protection filter, band-pass filters) that divide the frequency spectrum into separate channels. Each filter handles specific frequency bands, allowing the system to process multiple communication signals while isolating the GNSS receiver from interfering frequencies

Inventive Principle:

Principle #1Segmentation

2Power

If the ELT transmits high power 406 MHz emergency signals, then emergency location capability is improved, but the GNSS receiver sensitivity degrades due to transmitter interference

Engineering Contradiction:

Improveemergency signal transmission powerVSAvoidGNSS receiver sensitivity

Core Design Contradiction:

PowerVSMeasurement precision

Solution Approach 1:

The triplexer-EMI protection filter circuit serves as a mediator that allows the 406 MHz transmitter to operate at high power while simultaneously protecting the GNSS receiver from the resulting interference. The filter selectively blocks the 406 MHz frequency from reaching the GNSS receiver while allowing GNSS frequency bands to pass through

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the harmful effect of high-power 406 MHz transmissions into a manageable issue by using the filter circuit to redirect and block the interference. The same high-power transmitter that causes interference is utilized for its primary emergency location function, while the filter transforms the potential harm into a controlled signal path separation

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The solution effectively isolates the GNSS receiver from harmful RF frequencies and EMI, ensuring its sensitivity and accuracy in providing precise navigational location information during emergency transmissions and protecting it from degradation throughout all flight phases.

Implementation Method 1

The 406 MHz blanking switch protects the GNSS receiver from damage and receiver degradation during high power 406 MHz transmissions by providing isolation between the transmitter of the ELT and the GNSS receiver

Methodology Applied

Scientific EffectElectromagnetic isolation:

Implementation Method 2

A pair of different SAW filters, between the antenna and the GNSS filter provide filtering to prevent the ELT GNSS receiver sensitivity degradation from various unintentional RF frequencies

Methodology Applied

Scientific EffectSurface acoustic wave filtering: Surface Acoustic Wave

Implementation Method 3

The GNSS high-pass filter and the No. 1 and No. 2 SAW filters also protect the GNSS receiver from high-power 121.5 MHz or 243 MHz transmitters or their harmonics from these transmitters during their transmission

Methodology Applied

Scientific EffectHigh-pass filtering: Filter (electronic)

Data Source

PatentUS12019164B1Unintentional RF radiators filter protection for a cospas sarsat emergency locator transmitter (ELT) GNSS receiver

Publication Date: 2024.06.25 ACR ELECTRONICS INC

AI summary

This invention relates to an emergency locator transmitter (ELT) that transmits an emergency signal to a global navigational satellite system (GNSS) indicating an aircraft crash location, or an aircraft distress tracker event signal that triggers the ELT to provide location of the aircraft, the ELT including a GNSS RF receiver. The invention ELT includes 406 MHz RF signal blanking switch, a GNSS high pass filter, RF radiator and EMI filter protection for the GNSS receiver to protect the GNSS receiver from 406 MHz emergency signals, unintentional RF radiators and electromagnetic interference (EMI) typically found in aircraft.