Instruction manual
DDF1 32
Direction Indicator
Adjust the frequency of the audio generator very slowly around 500 Hz while
observing the LED display. You should see the direction indicating LEDs
around the green center LED illuminating. The LED illumination should ro-
tate clockwise when the frequency of the generator is set slightly lower than
the antenna rotation frequency. (Only one LED will be on when the fre-
quency of the generator equals the antenna rotation frequency.) The display
should rotate counterclockwise. The audio generator must be capable of
very fine frequency adjustment in order to observe the transition. All LED’s in
the display may appear to be on if the signal generator frequency is just
10Hz different from that of the antenna rotation frequency determined by U4.
It is interesting to observe the sharpness of the digital filter on pin 1 of U2 on
the oscilloscope as the display makes the transition from counterclockwise.
You can see the simulated Doppler tone of the generator come out of the
noise, peak and return into the noise as the transition takes place.
Calibration Control
Verify the function of the calibrate control by adjusting the audio generator
equal to the antenna rotation frequency. At this point, only a single LED will
illuminate. Rotate the calibrate control through out its range and observe the
direction indicating LED "move" around the display. The range of movement
should be more than 360 degrees. The direction indicating LED may move
slightly if the generator frequency drifts. It is very difficult to keep the gen-
erator frequency synchronized exactly, but that's not necessary in this test.
Disconnect the signal generator and reconnect the speaker to the receiver
audio input terminal.
Antenna Switcher
Verifying proper operation of the antenna switcher sequencing circuit re-
quires only a DC voltmeter. Connect the antenna switcher to the Doppler
RDF unit and position the four mag-mount antennas on a table.
Remove the whip antennas from all the mounting boards for this test
It is essential that the antennas be turned on in sequence to emulate an an-
tenna spinning in a circular pattern for the Doppler RDF unit to operate cor-
rectly. A single antenna turned on out of sequence is enough to produce a
bogus RDF reading. It does not matter if the antenna spins clockwise or
counterclockwise.
Scan/stop switch S2 stops the antenna from spinning. Close and open S2
until the voltage on terminal J2 pin 1 reads +1.4V. Pins 2, 3 and 4 should all
read near 0V. Pin 1 is the antenna enable signal for antenna 1. Label the
corresponding mag-mount antenna on the table as antenna 1. Close and
open S2 until the voltage on terminal J2 pin 2 reads +1.4V. Pins 1,3, and 4
should all read near 0V. Pin 2 is the antenna enable signal for antenna 4