A good GNSS receiver should bring in ALL of wideband GNSS signals and reject all other unwanted signals. We announced the existence of this technology months ago for the L1 band. Now we have improved this filter and added similar protection for all other GNSS bands.
The figure above shows the frequency response of our filter for L1. As shown in this figure, it allows complete, undisturbed L1 signals in and defends against any other signals outside this band. In particular it defends against LightSquared signals of 10L, 10H, and 10R (Handsets). The filter drops down quickly, at the rate of 12 dB/MHz outside the GNSS band.
Figure on the right shows the frequency response of our filter for other GNSS bands. Although there are no requests for other systems near these GNSS bands yet, our filters have protection if this happens in future.
Interference is not limited to wideband wireless systems. Harmonics of other transmitters can occur anywhere and we see it as an essential requirement to protect all GNSS bands in our receivers against all interferences as much as possible. Our technology allows us to do a better job today.
Our effort in protecting the GNSS bands did not end with designing appropriate filters. We needed to a) prove that these filters work, b) prove that these filters not only do not degrade the performance of GNSS receivers but improve performance, c) devise features that any person can use to test our receivers, and d) devise features where users can readily see the effect of interferences that may fall within the GNSS bands in some areas or see the effect of intentional jammers that are marketed these days with prices as low as $400.
So, how to recognize interferences and how to quantify their effects?
Without proper equipment and knowledge any technical issue can turn political and lobbyists, politicians, bloggers and editors will take over and stars of generals and titles of people will eclipse the scientific facts.
To study the effect of interferences in some official tests, they had to use very expensive equipment in highly sophisticated laboratories, employ experts, and then wait for several weeks to get the test results. These results were not conclusive and therefore were open to interpretation.
It is our claim that these new innovative test features that we have embedded in our GNSS receivers a) are much more comprehensive than those done in laboratories with a roomful of equipment, b) can be used by any novice user in the field, and c) provide instantaneous results.
The embedded features perform five different highly sophisticated tests and show the results automatically in a user friendly and easy way. A push of a button activates all these tests in the background while user can perform their normal survey or other positioning tasks.
For each GNSS band we have embedded features to A) quantify interferences by AGS numbers, and its variations, B) visualize interferences by the AGC control voltage graph, C) visualize and quantify in-band-interferences by the spectrum graphs deep inside the signal processing section, D) show deviations of C/N0 from standard numbers, E) measure and show any missing ‘heartbeat’ inside the carrier phase tracking system with our new sophisticated and comprehensive real-time cycle slip indicator.
J-Shield option protects GNSS bands on the first stage of antenna LNA system. Currently it is available on GrAnt-G3T, RingAnt-G3T, and internal antenna of TRIUMPH-1. Soon we will release it on GrAnt-G3, AirAnt-G3 and AirAnt-G3T. To order this option, select the J-Shield box in the order page of the related product.