User`s manual

5
Chapter 3
Mobile Antenna Installation
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 1/4 wavelength apart on the car’s roof.
Note: To 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.) Locate the
summer near the back of the car (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 not free to move around and touch the antenna elements. Route the control
and RF cables through a rear window. For mobile operation in the 700-1000 MHz band,
antenna DDF7064 should be mounted directly on top of the RF summer. This antenna
provides an extended ground plane, a wind shroud, and four stub type antennas built into
TNC connectors. Place the assembled RF summer/antenna in the center of the car roof. Be
sure to use the safety strap provided with the DDF7064 antenna.
The photos below show typical installations.
Chapter
3
MOBILE ANTENNA INSTALLATION