Knowledge Base

Custom Cavity-Type Notch Filter for Mitigating GPS/GNSS Interference from Iridium Data Transmitters

The Iridium satellite communication system uses the 1616-1626.5 MHz band to uplink with orbiting communication satellites. UNAVCO Inc. uses iridium communication links to download GPS data from remote GPS stations located at high latitudes. The L1 frequencies broadcast by GPS, Galileo and GLONASS satellites are 1575.42 MHz, 1575.42 MHz and 1602 MHz + n × 0.5625 MHz, respectively (each GLONASS satellite uses a unique frequency). The proximity of the Iridium frequency band with the L1 frequencies of the GPS, Galileo and GLONASS systems leaves GNSS receivers susceptible to interference from Iridium data transmissions. Interference from Iridium transmissions can cause cycle slips and loss of lock on the carrier and code phases, thereby degrading the quality of GNSS observations.

The broader gain pattern of the Low Noise Amplifiers (LNA) installed in many newer GNSS receivers/antennas (shown below) can increase the impact of near-band RF interference on tracking performance.  Our testing has shown that the quality of data collected at sites collocated with iridium communications is highly degraded for antenna separations exceeding 100m. Using older GPS antenna models (e.g. TRM29659.00) with newer GNSS enabled receivers can reduce this effect. To mitigate the effects that iridium data transmissions have on receiver tracking performance, we tested a custom cavity-type notch filter designed to attenuate the Iridium RF band. The filter has a >20dB rejection at 1616-1626.5 MHz.  Test results when using the filter have shown excellent GPS data quality at antenna separations of ~30 m. Determining what impact the filter has on GLONASS and Galileo observations will require further testing.  Future investigations will also include alternative RF mitigation methods, including RF shielding.

Above: A custom cavity-type notch filter designed to mitigate the interference caused by Iridium communication transmissions.

Above: Gain vs. frequency for a Trimble GPS Choke Ring antenna LNA compared with a Trimble GNSS Choke Ring LNA. The gain pattern for the newer GNSS choke ring has been widened to improve the tracking of GNSS signals.

Above:  Gain (dB) vs. frequency (MHz) measurements for three different Device Under Test (DUT) combinations. 1) Reactel custom cavity-type notch filter. 2) Low Noise Amplifier (LNA) from a Trimble GNSS Choke Ring antenna. 3) Trimble LNA + the Reactel notch filter. Dashed black lines indicate the L5, L2 and L1 GPS frequencies. The dashed blue lines show the frequency band used by Iridium communications for uplinking to a satellite.  The notch filter has <0.5 dB insertion loss at the L1, L2 and L5 frequencies, and has a greater >20 dB rejection at 1616-1626.5 MHz.

Attached Files
There are no attachments for this article.
Comments (1)
Comment by Bottes UGG Classic Mini Pas Cher on Mon, Jan 6th, 2014 at 4:08 AM
13. Manager Jim Leyland
Security Code Security Code
Related Articles RSS Feed
Trimble TRM59900 Ti-Choke Ring GNSS Antenna Test Report
Viewed 8801 times since Wed, Oct 2, 2013
AOA Receivers Benchmark Test (1998)
Viewed 4316 times since Thu, Sep 10, 2009
Topcon GB-1000 First Article Receiver Testing
Viewed 3531 times since Thu, Oct 30, 2008
The Role of Multipath in Antenna Height Tests at Table Mountain (paper, 1995)
Viewed 3116 times since Wed, Mar 24, 2010
Real Time GPS Data Transmission Using VSAT Technology (paper, GPS Solutions, V5 N4, pp. 10-19, 2002)
Viewed 4463 times since Mon, Jan 19, 2009
1995 UNAVCO Antenna Height Tests
Viewed 3262 times since Wed, Mar 24, 2010
Power Draw Profile for Trimble NetRS and Iridium Systems
Viewed 6531 times since Sat, Aug 28, 2010
Iridium & GPS/GNSS Inteference from Iridium Data Transmitters
Viewed 19836 times since Mon, Oct 24, 2011
Digitizing Resolution of the Leica GR10 Receiver
Viewed 3827 times since Thu, Feb 3, 2011
The Effect of Antenna Covers On GPS Baseline Solutions (1997)
Viewed 7548 times since Wed, Mar 24, 2010

Last modified: 2019-12-27  16:36:35  America/Denver