2-58
CHASSIS MODIFICATIONS
D
AILY 4x4
Base - May 2007 Print 603.93.761
Electrical System: Modifications and Drawing-Off Power
Amateur equipment for CB and 2m band.
The installation of CB (27 MHz) and 2m (144 MHz) sets must use the power system provided on the vehicle. The connection
is made to terminal 30 of connector ST40.
The s ystems must be legally ty pe-approved and fixed (not portable). Install the transmitting part in a flat, dry area separate from the
electronic components of the vehicle, away from humidity and vibrations.
The an t enna must be installed outside the vehicle, possibly on a large metallic base as vertically as possible with the connect ion wire
leading downwards. Follow the instructions and the manufacturer’s warnings for assembly (see Figure 2.31).
• The SWR must be as close as possible to one. The recommended value is 1.5, while the maximum acceptable value must not
in any case be greater th an 2.
• The AERIAL GAIN values must be as high as possible and ensure sufficient spatial uniformity, normally with deviations from the
average valu e in the order of 1.5dB in the typical CB radio band (26.965- 27.405 MHz).
• The RADIATED CAB FIELD value must be as low as possible. We su ggest < 1 V/m as a quality target. In any case, the value
must not exceed limits imposed by current European guidelines.
• The aerial must therefore always be located outside the passenger compartment.
It is advisable to consider t he following guidelines to ensure th at the radio-cable-aerial is working effectively and assess whether the
aerial is adjusted:
1) If the SWR is higher on low channels than high channels, extend the aerial.
2) If the SWR is higher on high channels than low channels, shorten the aerial.
After adjusting the aerial, it is advisable to re-check the SWR on all chann els.
The best position to install the aerial is the c entre of the roof because the earth plane is proportional in all directions, while installation
on a side or any other part of the vehicle makes the earth plane proportional to the vehicle mass.
Cables involved in the installation s shou ld be connected an d positioned taking care to:
- Use a top-quality, low-loss coaxial antenna cable with the same impedance as the transmitter and the antenna. (see Figure 2.32).
- The co axial cable run must be at a suitable distance (minimum 50 mm) from pre-existing w iring (TV, radio, telephone, amplifiers
and other electronic devices) to prevent int erference and malfunctionin g. Ensure t h e minimum distance from th e metallic struc-
ture of the cab. Cable installation on the left or righ t-h an d side is preferable.
- Clean th e lower part of the hole made in t h e body for in stalling th e antenna in fixed position so that the antenna su pport is
perfectly connected to the vehicle earth.
- The coaxial cable connecting the antenna to the radio must be fitted with the utmost care. Avoid curves or bends which can
pinch or distort the cable. Avoid tangling. Shorten the wire as much as possible. Remember that any imperfections in t he coaxial
cablewillcausesevereinterferencefortheradiotransmitter.
To Next Page
Loading...
Need help?
General
