What is a GP-Blocker?

A GP-Blocker is designed to turn off the antenna port of the time server in case of GNSS spoofing/jamming or low GNSS signal quality. The connected time server loses satellite signals and enters the “Hold Over” mode.

The GP-Blocker is installed between the time server and the GNSS antenna. It is the simplest way to integrate GPSPATRON and the time servers in case of brief setbacks when the accuracy of PPS of the time server in the “Hold Over” mode does not exceed the accepted limits.

Features of GP-Blocker:

  • RF switch for blocking high-frequency GNSS signal;
  • DC switch to simulate the power failure of the antenna;
  • Noise generator for guaranteed blocking of high-powered, counterfeit signals;
  • Backup power from the time server.

Embedded Noise Generator

The output power of satellite transmitters is only 60 watts with an average orbit of 20,000 km. As a result, the power of signals’ on the earth’s surface is about minus 150 dB/W. This value is below the environment noise level by 10 – 30 dB.

The average output power of a spoofer based on SDR HackRF One does not exceed 10 mW.  The power of “fake” signals will be about minus 90 dBW at a distance of 50 meters in open space. This is 60 dB greater compared to the power of genuine signals. This is enough power for an asynchronous attack. A synchronous attack can be conducted at a distance of 30 km.

RF switch with 90…110 dB isolation level can only block phony signals from HackRF One at a max distance of 5 meters with an asynchronous attack scenario. However, if the spoofer’s transmitting antenna is closer or a directional antenna with a high gain is applied, the blocking power may be subdued.

A military-scale spoofing application can use a high-power RF transmitter (100W or more). In that case, the RF switch is unable to block the bogus signal. The GP-Blocker’s embedded noise generator jams false signals and increases the blocking level up to 200 dB.

DC Switch

Many time servers measure the antenna’s preamplifier current to detect cable breaks. If the current value tends to zero, the time server generates an error and switches to Hold Over mode. Thus, the DC switch provides additional protection against the most dominant synchronous spoofer.

What Happens When the GP-Probe is Disabled?

Since GPSPATRON protects critical infrastructure elements, it is essential to guarantee the operability of the system in case of a GP-Probe failure or a power outage.

Although the GP-Probe is equipped with two independent power sources, a surplus power source must be provided in case of a power loss or a GP- Probe failure. In ordinary conditions, the GP-Probe powers the GP-Blocker.

In case of power loss, the GP-Blocker activates the emergency mode and obtains the power from the GNSS antenna port of the time server’s GNSS module.

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