5
Chapter 3
Mobile Antenna Installation
Note:
Do not place the direction finder antennas near a transmitting antenna. Transmitting
too close to the DF antennas can cause catastrophic damage to the summing unit.
Four antenna elements are used for mobile operation. At frequencies below 500 MHz, magnetically
mounted quarter wave whips are used. These antennas must provide a good coupling to the ground
plane, and must be of exactly the same type. It is especially important that the coaxes used have the
same length. Doppler Systems antennas DDF7061 and 7062 use the same magnetic mount base and
cover the frequency ranges 88-136 and 136-500 MHz respectively. Cut the whips to resonance using
the chart provided with the antennas and space them approximately 1/8 to 1/4 wavelength apart on
the car’s roof. (See table for spacing recommendation)
Antenna Spacing Recommendation
Frequency
Range
(MHz)
Low High
Spacing
(in)
Spacing
(cm)
100 120
23.7
60.2
120 144
19.8
50.2
150 180
15.8
40.2
180 220
13.1
33.2
220 250
11.1
28.1
250 300
9.5
24.1
300 360
7.9
20.1
360 430
6.6
16.8
430 500
5.6
14.2
Note: T
o avoid damage to the input circuitry used in the RF summer, touch the antenna ground plane before
attaching the whips to the magnetic mounts.
It is important that the vehicle provides at least 1/4 wavelength of ground plane outboard of the
antennas.
Place the RF summer (DDF7080) on the car with the cables oriented towards the rear of the car.
Connect the magnetic mount antenna cables to the corresponding TNC connectors on the RF
summer. (That is, the left front antenna to the left front connector, etc. See Figure 1.) Locate the
summer near the back of the car (e.g. the lid of the trunk) so that the magnetic mount antenna cables
do not have excessive slack. Secure the four antenna cables together with nylon ties so that they are
Chapter
Chapter
Chapter
Chapter 3
3
3
3
MOBILE ANTENNA INSTALLATION
MOBILE ANTENNA INSTALLATION
MOBILE ANTENNA INSTALLATION
MOBILE ANTENNA INSTALLATION
Summary of Contents for DDF7000
Page 12: ......
Page 25: ...21 Fixed Site Antenna Assembly Figure 15 UHF to THF mast with cables ...
Page 26: ...22 Doppler MPT Users Manual User s Guide Figure 16 THF Antenna Frame Installed ...
Page 34: ...30 Doppler MPT Users Manual Revision D Figure 24 Direction Finder with RS232 receiver ...
Page 48: ...44 Doppler MPT Users Manual Revision D J5 in master position J5 in slave position ...