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Do You Need a Screened Enclosure to Test a GNSS Receiver?
The traditional logic that all RF testing should be carried out in a screened enclosure has much to recommend it. But do you always need to go to this level of protection when testing a GNSS receiver with a simulator? The short answer is no, because the preferred method of testing is to remove the antenna from the equation and connect the simulator directly to the receiver.

However, there will be occasions where the antenna cannot be removed. And there will also be certain acceptance tests that demand the testing of the complete system – including the antenna.

The screened enclosure (or TEMS cell), which only needs to be large enough to accommodate the test piece and a dipole antenna to emit the simulator signals, will act as a Faraday cage to keep unwanted signals from the outside away from the receiver's antenna. And while testing will inevitably be performed indoors, within a building that itself will act as a Faraday cage so far as live-sky GNSS signals are concerned, the building will also be home to its own array of intentional wireless signals and accidental radio frequency interference that could compromise the validity of the receiver tests. What's more, RF-reflecting surfaces within the test area can also create complex multipath effects that could also compromise the results.

A wide variety of screened enclosures are available with a wide range of sizes and a huge variation in costs. The enclosure must be large enough to accommodate the unit under test and the half-wavelength dipole antenna, and should provide RF shielding of at least 40dB at 1.5GHz and have all its internal surfaces covered in suitable RF absorbing material to minimise internal reflections and multipath effects.

For more information on the importance of antenna modeling in GNSS testing download the FREE Spirent Application Note "Keeping your eye on the sky".
By: Andy Walker - 6/15/2011 7:47:41 AM
Tags: GNSS Receivers

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