Chapter 4 — Antenna Hacks 75
FIGURE 4-14: SmartSolar solar charger and power pack
Setting Up a Reradiating Antenna in a Car
This section describes how to set up a reradiating antenna in a car. Before you start, you have to make some decisions:
Consider how you are going to power your reradiating antenna and your GPS while it’s in the car. If your car has a 12-volt cigarette adapter, then that can be used (add a splitter if you need to double up on the sockets available). If you need to tap into the power supply to hardwire the power supply, remember to add a fuse to the circuit (2A will work).
Consider antenna placement carefully. The best place is the highest point on the vehicle. Normally, the spot that has the best exposure to the sky is the roof, but if you usually have a roof rack, then this might need to be reconsidered.
Is the antenna going to be permanently fixed to the vehicle or is it temporary? If it is going to be a permanent addition to your vehicle, I suggest you attach it using stainlesssteel screws or bolts, and use silicone to waterproof any holes you make. You can achieve a temporary setup with a magnetically mounted antenna. These antennas often have a
76 Part I — Hardware Hacks
low profile, so they can be left attached and will withstand normal driving speeds and high winds. For a permanent antenna, you should take the cable into the vehicle through a hole near the antenna. For a temporary job, it’s a better idea to take the cable in through the door frame. There is usually enough give in the rubber seal, and as long as you don’t route it at the top of the door, it is unlikely to let in water.
Consider where you are going to place the reradiator. The usual place for this is on the front windshield, attached using the suction cups that are supplied with most reradiating antenna units.
After you have answered the preceding questions, you can set up the reradiating gear:
1.Place the antenna in a suitable spot. Whether you plan to fix the antenna permanently or temporarily, attach it temporarily initially so that you can test the location before drilling holes in the bodywork.
2.Route the cable. The passenger door is the typical route into the vehicle (unless you are planning on a permanent connection — but even then, don’t drill the holes just yet!). Tape can be used to fix the cables and keep them in place, as can cable ties. Don’t use wire — this can cut through the cable. Route the cable from the antenna to the location you have chosen for the reradiator (on the front window).
3.Sort out the power. Route the wiring to the spot where you plan on putting the reradiator.
4.Add the reradiator. Attach this securely using the suction cups and loop any remaining cables tidily to keep them under control.
Testing the System
Now it’s time for a test drive with the GPS system running. This can be a simple test in which you drive around and examine your route afterwards or you can plot a few different routes and see if the GPS will take you there.
Also test the reception from the reradiator at various points in the vehicle. Remember that the signal from the reradiator is the same frequency as the signal from the GPS satellites (just brought a lot closer) so obstructions, especially people, can adversely affect the signal. If you find that the placement is less than ideal, try raising it higher.
If you have installed a temporary reradiating antenna system, you are not done. After your first drive around, you might decide that you want to make a few adjustments to the setup (moving the antenna or rerouting the cables differently).
Making the System Permanent
Now’s the time to make the setup permanent (if that was what you had planned in the first place). Ensure that you’re happy with the placement of the various antennas and cabling, and think about any changes or additions you might want to make to your vehicle in the near future that might mean undoing any work you do now. Moving something held in place with a suction cup is one thing; moving something after you have drilled holes for it is another.