Direction Finder Overview
The following paragraphs give an overview of the Doppler direction finder. They consist of two parts. First of all, they consist of a base unit, which does the signal processing. Secondly, they contain an antenna unit, which controls the multi-element antenna array. The base unit issues commands to the antenna (for example, the sweep rate) via an RS485 data link. The same serial link synchronizes the rotation of the antenna to the signal, processing in the base. The system supports many possible arrangements of antennas, processors, receivers, and network configurations. We have illustrated the most basic fixed site arrangement below.
Basic Fixed Site Arrangement
In this configuration, a single processor unit connects to a single antenna and a single receiver. The PC displays bearing data. The PC also controls the DF and the receiver. The DF processor provides a host USB port for connection to the receiver, thereby allowing it to be remotely controlled. The receiver processes audio to compute the bearing angle. It is also filtered to remove the commutation tone and drive the loudspeaker shown. The USB port reads the received signal strength (RSSI). It is sent, along with the bearing data, to the PC.
Each fixed site DF antenna has a bandwidth of one octave (115-250, 250-500 and 500-1000 MHz). The antennas themselves accomplish antenna switching. This, therefore, allows one to run a single control cable and a single coax cable to the stacked antenna array. For example, see the diagram below.
Users can simultaneously monitor multiple channels and compute bearings using the same DF antenna. Multiple processors connected together This is accomplish this in a daisy chain arrangement. The Master DF controls and synchronizes the antenna and the Slave DF processors. While we show two channels below, the scheme can extend to thirty-two.
In mobile operation, replace the fixed site antenna with a magnetic mounted RF summing unit. Using the MPT User Interface software, one may construct a simple homing direction finder by simply adding a narrowband FM receiver.
When running an application such as TargetTrack, connect a laptop to the MPT using the Ethernet port. The GPS will connect to the MPT USB port either directly or through a USB-to-serial converter. You may also connect a compass or yaw rate sensor.