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Handheld Users Group - Interference Hunting

Using Direction Finding to Locate Interference in Citiers

Using Direction Finding to Locate Interference in Cities

Interference hunter


Identifying an interfering signal means you’re half way to solving your network problem, however the hard part may yet remain – finding the source. This can be particularly tricky in an urban environment, where congestion, large buildings, and multiple networks reside. Using the proper direction finding methods can help you locate the interference cause faster and more efficiently.

In cities, the main propagation paths that the signal follows will probably be multiple bounces off buildings. In this scenario, a good method is to walk to an intersection and point your antenna (either a Yagi beam, log-periodic, or flat panel directional antenna) attached to an Anritsu Spectrum Master™ down each road. To find the best direction to the emitter, follow the strongest signal until it there is a radical change in the direction in which the strongest signal arrives.

As you move around, you may come close to other transmitters operating at different frequencies that can saturate the spectrum analyzer front end. Eliminate this possibility and subsequent problems with strong out-of-band signals by using a bandpass filter tuned to the frequency range of interest.

Eventually you will walk past the emitter. You’ll know when this happens because the direction of the strongest signal changes significantly. At this point try triangulating the signal. If the signal is still being received via indirect paths, triangulation will yield different answers, depending on your exact position and the signal with the strongest bounce. By this time, you probably will be receiving a signal directly from the emitter, so more traditional direction-finding techniques will work.

Proper direction-finding techniques are also important in locating interference sources in other environments, such as fixed networks and Doppler arrays.

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