A GPS filter with DC pass is a specialized RF (radio frequency) component designed to filter out unwanted signals while allowing both GPS signals and DC voltage to pass through.
This is important for applications where power must be delivered to an active antenna or amplifier over the same coaxial cable carrying the GPS signal.
Table of Contents
🧩 Breaking it Down
- GPS Filter: Removes out-of-band noise, interference, or nearby signals that can disrupt GPS reception (such as LTE, Wi-Fi, or radar).
- DC Pass: Allows low-voltage DC power (usually 3–12V) to pass through the same coaxial cable—this is used to power active GPS antennas or low-noise amplifiers (LNAs).
⚙️ How Does It Work?
A GPS filter with DC pass is usually placed in-line between a GPS receiver and an active antenna. Here’s what it does:
- Filters unwanted signals outside the GPS frequency band (L1 at 1575.42 MHz).
- Passes clean GPS signals to the receiver.
- Allows DC voltage from the GPS receiver (or bias tee) to travel up the coaxial cable and power the antenna or LNA.
It achieves this by using internal circuitry—capacitors and inductors—to block RF interference while allowing DC power through.
🌐 Applications of GPS Filters with DC Pass
These filters are essential in many precision and professional applications:
🚗 Automotive & Telematics
- In fleet management and connected vehicles, these filters maintain signal integrity in noisy environments (e.g., near LTE modems).
🛰️ GNSS Survey & Mapping
- Used with high-precision GNSS receivers for land surveying, marine navigation, and agricultural automation where accuracy is critical.
📡 Timing & Synchronization
- Telecom networks and data centers rely on GPS-disciplined clocks—filters reduce signal degradation that can affect synchronization.
🧪 RF Test & Measurement
- Engineers use these in test setups to ensure clean GPS signals during hardware validation or device certification.
🏢 Indoor GPS Repeater Systems
- When GPS signals are rebroadcast indoors, filters with DC pass are used in conjunction with inline amplifiers and splitters.
🧰 Example Setup
Here’s a typical configuration:
GPS Receiver ← Filter with DC Pass ← Coax Cable ← Active GPS Antenna- The receiver sends 5V DC through the coax to power the antenna.
- The filter blocks LTE or other out-of-band interference and only allows GPS signals + DC voltage.
✅ Advantages
- Improved GPS accuracy by reducing interference.
- Simplifies wiring—no separate power cable needed for powering the antenna.
- Protects sensitive receivers from strong nearby signals.
⚠️ Things to Consider
- Make sure the DC pass rating supports the required voltage and current.
- Choose a filter with the right frequency range for your GPS band (L1, L2, L5).
- Check insertion loss—some filters may slightly attenuate the GPS signal.
🔚 Conclusion
A GPS filter with DC pass is a small but powerful device that plays a crucial role in maintaining signal clarity and system simplicity in GPS-based applications. If you’re working with autonomous systems, timing solutions, or RF testing, this filter is a must-have for optimal GPS performance in complex environments.