Automatic Direction Finding Step By Step - L3Harris Narda SignalShark User Manual

Automatic Direction Finding
A bearing measurement or bearing cycle is a sequence of signal power measurements for
each antenna element in combination with four phase shifters.
The parameter "Cycle Time" is the time needed for one complete bearing cycle. For the
circular arrays it is the result of:
1 omnidirectional measurement
+ 9 (antenna elements)
x 4 (phase shifters) measurements
= 37 power measurements
The filter settling time equals the minimum configurable measurement time.
The minimum configurable measurement time depends mainly on the current CBW
settings.
Cycle Time = 37 x Meas. Time + 37 x filter settling time.
In general: Broader CBWs allow shorter cycle times down to 1.2 ms.
SignalShark calculates a so called covariance vectors out of this power measurements for
every bearing cycle. This covariance vector is then correlated to stored reference data to
evaluate the azimuth and elevation angle of the bearing.
The omnidirectional power and spectrum of the reference antenna element are also
measured at the end of each bearing cycle, so the measurement results consists of bearings,
as well as omnidirectional level and spectrum values This makes it possible to monitor
changes in the signal level or spectrum concurrently with the bearings. Thus, you can
optimize your bearing settings to the signal of interest and monitor the adjacent channels.
Following three conditions must be met to get a valid bearing:
1. The average power of the signal at the reference element is the same during all four
power measurements for a single antenna element.
2. The signal to noise ratio is sufficiently high during the entire bearing measurement time.
3. The angle of arrival does not change during the entire bearing measurement time.
The SignalShark simplifies localization of transmitters by autonomously evaluating all the
available bearing results and plotting them on a map. It uses a statistical distribution of
bearing lines that represents the uncertainty in the bearing. The result is a map on which the
possible locations of the transmitter are plotted and color-coded according to their probability.
Red corresponds to a very likely and blue to a very unlikely transmitter position. The
SignalShark also draws an ellipse, which marks the area where the transmitter has a 95%
probability of being located, and its center is the estimated position of the transmitter.
When bearings are taken under non-ideal conditions, such as in an urban environment, the
uncertainty in the bearings is much more dependent on the environment than on the ADFA.
Nevertheless, if enough bearings are taken from enough locations, the localization algorithm
of the SignalShark will generally result in a convergence on the actual location of the
transmitter, even in urban surroundings. To speed up and optimize the localization process,
an ADFA can be attached to the roof of a vehicle to take bearings from random positions in
the suspected area. This allows fast and reliable localizations even in challenging
environments

Automatic Direction Finding step by step

The following recommended steps will lead you through the direction finding process on a
most direct way possible and without too many trial and error.
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