How To – Mobile Installation
Some careful considerations are required to install a mobile transceiver into a vehicle. This example shows how I installed my Yaesu FT-7900 dual band radio.
Below is a list of a few things you should think about before simply throwing the radio into the vehicle.
Getting power to the radio
Possibly the most important consideration is the power source. A quick glance around inside the car and there is the most convenient power source.
STOP, don’t even think about using the cigarette lighter socket, or aux power socket as they are now commonly labelled.
Why not? There are a variety of reasons why you shouldn’t use this handy, already available source.
Probably the most important reason is the current requirement. It is highly unlikely that the socket or it’s wiring can handle the current needed during transmission.
Virtually all modern vehicles use the CAN bus system. This system is basically a computer network using the vehicle’s wiring which allows the various ECU’s “talk” to each other.
As a consequence, the radio can pick up unwanted noise through this power source. Of course, it’s also possible that the radio could introduce noise into the wiring, thus disrupting CAN bus communication.
Where should we get the power from? The manual that comes with the radio will most probably advise that connections are made directly to the battery.
In fact, every manual I’ve read to date does recommend this method including the manual for the Yaesu FT-7900.
How you route the wiring to the battery is a matter of personal choice, but more importantly, making sure it’s safe.
Choice of mobile antenna mount
What’s the best method of mounting my antenna? You may as well ask “how long is a piece of wire?”
Many factors affect the choice and method of mobile antenna mounting.
The magnetic based (mag-mount) may be the best option for some. While others may prefer to drill a hole and mount it directly to the bodywork.
Alternatives include rail mounts, possibly one of the preferred options if your car has roof bars.
The drawback with this method is you MUST ensure the rails are well grounded!
Both of these clamp onto the lip of the boot lid or tailgate.
They are very similar in design to each other, the major difference being the hatch mount tends to have a greater degree of adjustment. This is to take the steeper angles often found on a tailgate into consideration.
Gutter mounts are available, again these are similar to the boot and hatch mounts, although these are seldom seen as most modern cars no longer have gutters.
My best option was to use a hatch mount. The reasons for my choice were twofold, firstly, the car is a hatchback, secondly and most importantly, being a nice new car I did not want to drill any holes or damage the bodywork.
The coaxial cable is routed upwards to the top edge of the tailgate, some slack has been left to allow opening and closing of the tailgate.
The coax then follows the line of the boot rubber to the bottom of the aperture. At this point a drip loop is made thus preventing water ingress, before entering at the bottom edge of the boot.
Self adhesive cable tie anchors and cable ties prevent the coax from moving around, consequently, this prevent the cable becoming trapped, damaged or crushed.
Mounting the Yaesu FT-7900 Face
A complete kit (YSK 7800 separation kit) allowing mounting of the front panel away from the radio body may be purchased. The kit was included with some radios therefore eliminating the need to purchase it separately.
Included in the kit are a mounting plate for the front panel along with two cables. One cable connects the front panel to the main unit, the other allows use of an extension speaker.
For the same reasons that I didn’t want to drill holes for mounting the antenna, a number of different mounting methods were considered, from mobile phone holders, double-sided sticky pads etc.
In the end, I opted to use an air vent to mount the radio face plate. Cable ties were threaded into the air vent, wiggled around the back of the air-direction slats and back out again.
A small piece of non-slip foam matting was placed between the mounting plate and vent which was then held in place with the cable ties.
NOTE: Be sure that the airflow can be turned off to prevent hot air blowing onto the radio face when the heater is on.
Mounting the Yaesu FT-7900 Body
A lot of new vehicles are supplied with emergency tyre inflation kits with spare wheels being an option as in the case of mine. This leaves a huge aperture in the floor of the boot where the spare would be placed if it was fitted. It was this space into which I fitted the body of the FT-7900.
Holes in the FT-7900 mounting bracket lined up nicely with holes that are in the spare wheel securing bracket and so I simply bolted the radio bracket to it. Bolting them together also helps to ensure the radio is grounded.
The cables from the face plate are routed around the door rubber to floor level where they are tucked between the carpet and plastic trim along to the back of the car.
Once at the back of the car, the cables pass through a small gap where the rear seats hinge for folding down, into the boot.
The excess cable is simply wound up and tied to the power cable to prevent it from moving and rubbing against the vehicle thus preventing the insulation becoming damaged.
It can be seen in the picture, the car battery is placed in a well just in front of the spare wheel well. Obviously, this was extremely helpful for the power wiring. At the time the picture was taken, the antenna feed was not yet installed.