Fox Hunt

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A new feature from version 7.8.9 is the 'Fox Hunt'. When a Radio Direction finding event is taking place, radio bearings to the 'Fox' can be taken from a number of locations, and where these cross is a possible Fox site. To demonstrate the use of this feature, I have moved the Mobile Unit in my Base Network to a central road map position as shown below, and the azimuth bearings from the two Hand Held Units HH and HH-2 will be used.

Opening 'Tools/Fox Hunt' generates the pane below, where bearings from up to 6 Units can be entered plus the length of the generated azimuth line defined. The 'width' here has been set to 0˚ to give a direct bearing line.

In practice the bearing wouldn't be entered to decimal degrees as above, as the uncertainty in the bearing would limit this to possible 5 degrees at best, but I cheated as I used the link azimuths from the Radio Link pane to obtain these values. A click on 'Draw' will then project the bearing lines on the map as shown. Closing the 'Fox Hunt' pane allows you to select how you wish to keep the picture as normal. This picture3 shows the effect when 'Keep in New Picture' is used.

It can be seen that the three bearing azimuths cross at the Mobile Unit, but for a more detailed view, the area round the crossing point can be Zoomed, and merged with a data source. Picture4 shows a merged Road map from Virtual Earth, converted to greyscale, with the Mobile Unit sited at a cross Roads.

Opening 'Tools/Fox Hunt' once more - which retains your previous settings - and pressing Draw, will now draw the azimuth lines on the Zoomed view to confirm that the plot is accurate on my Base Network at a range of 10Km!

In practice this sort of accuracy of location won't be achieved due to bearing measurement uncertainties, but the plot will accurately display the entered values.

If the Fox Hunt pane is opened once more, these bearing uncertainties can be taken into account by entering a 'width' value for them as shown. It should be noted that the maximum width which can be employed is 60˚.

and when plotted over the road map, this picture will result, showing the area where the mobile unit should be located.

By zooming into the 'crossover' area, merging with a road map once more, then forcing greyscale, the map below is generated - over which the bearing plot has been repeated from the three locations.

Illustrating the power of the technique.

There is no restriction on the allocation of the 'From' Unit, so this can be used for multiple bearing plots from a single unit if required when set as below.