SPECIAL INSTRUCTIONS FOR ELECTRONIC SUBSYSTEMS 5-23 E UROCARGO Euro 4/5 Choosing an antenna installation is of considerable importance to assure the transceiver apparatus the greatest performance. It must be of excellent quality and installed with the greatest care, also the position in which it is fixed is of fundamental importance; it deter- mines the efficiency of the antenna and therefore the capacity of the transmission.
Therefore the characteristics of SWR (Standing Wave Ratio), gain and electromagnetic field generatedmust beassured within certain limits, while the parameters of impedance, effective height, efficiency and directivity are deduced from the manufacturer’s technical information sheet. The installation of c.b. ham 2m appliances, mobile phones (gsm) and satellite navigation systems (GPS) must use the supply system already set up on the vehicle, making the connection directly to terminal 30 of connector ST40 (and 15 where necessary). This equipment must be type approved according to the law and be the fixed type (not portable).
Using transceivers that have not been type approved or applying additional amplifiers could seriously jeopardize the correct operation of the electric/electronic de- vices normally supplied, with negative effects on the safety of the vehicle and/or of the driver. CB and 2m band ham radio appliances The installation of C.B. (27 MHz), 2m (144 MHz) appliances must use the supply system already set up on the vehicle, making the connection to terminal 30 of connector ST40. This equipment must be type approved according to the law and be the fixed type (not portable).
Install the transmitting part in a flat and dry zone separated from the electronic components of the vehicle sheltered from moisture and vibration. The antenna must be installed outside the vehicle, preferably on a large metal base fitted as vertically as possible with the connecting cable turned downwards, observing the assembly prescriptions and the instructions of the manufacturer (see Figure 5.10). • The value of the SWR must be as near as possible to unity, the recommended value is 1.5 while the maximum acceptable value must in no case be greater than 2.
• The values of the ANTENNA GAIN must be as high as possible and assure a sufficient characteristic of spatial uniformity, char- acterized by deviations from the mean in the order of 1.5dB in the typical cb band (26.965-27.405 MHz). • The value of the RADIATED FIELD IN THE CAB must be as low as possible, as a quality objective we recommend In any case the limits set by the current European directive must not be exceeded. • For this reason the antenna must be always be set outside the cab. To determine proper operation of the radio-cable-antenna system and allow evaluating whether the antenna is calibrated, it is rec- ommended to take account of the following indications:
1) if the SWR is higher on the low channels than on the high ones it is necessary to lengthen the antenna; 2) if the SWR is higher on the high channels than on the lower ones it is necessary to shorten the antenna. After calibrating the antenna it is advisable to recheck the value of the SWR on all the channels. Installation in the middle of the roof is considered the best since the ground surface is proportional in every direction, while assembly on a side or on any other part of the vehicle makes the ground surface proportional to its ground. The connection and positioning of the cables that involve the installations must be done taking care to:
- use a coaxial antenna cable of excellent quality with low loss and having the same impedance as the transmitter and the antenna (see Figure 5.11); - for the aforesaid coaxial cable make a route that, so as to avoid interference and malfunctioning, has a suitable distance (min.
50 mm) from the pre-existing wiring and from other cables (TV, Radio, Telephone, Amplifiers and other electronic equipment), saving the minimum distance from the metal structure of the cab; application is preferable on the left or right side; - when installing the fixed antenna it is necessary to clean the bottom of the hole made in the bodywork, so that the antenna support is properly connected to the ground of the vehicle; - the coaxial cable joining the antenna to the radio must be mounted with great care, it is necessary to avoid bends or folds that can crush or deform. If the cable is too long, avoid pointless tangles, and preferably shorten it as much as possible.
It is wise to remember that any imperfection in the coaxial cable always causes serious trouble for the transceiver; Electrical system: modifications and drawing-off power Print 603.93.431 Base - January 2008