The ABCs of CB Installation

| December 20, 2004

All you need to know to change out a citizens band radio and stay loud and clear.

Without a citizens band radio to stay in touch with drivers around you on the highway, the road would be a lonely place. Conversation can make the miles speed by, not to mention all the valuable information you can get about traffic and road conditions.

If you don’t have a CB, need to replace a broken CB or want to upgrade to a fancier model, all you need are a few simple tools and the ABCs of swapping or installing one to save you money.

When you go to buy a CB, do your homework. “Buy one that’s really to your liking,” says Ramon Sandoval, product manager for CB radios at Cobra Electronics. “Do a careful brand and product analysis, and look carefully at all the features.”

One feature that can be helpful (if you’re electronically capable) during installation is an SWR (“standing wave ratio”) meter. While an external meter can be used, having one on the CB makes it easier to match the setting of the antenna to the radio so the outgoing signal will be properly distributed when you transmit.

Another consideration with some CBs is the polarity of your truck’s electrical system – whether it has a positive or a negative ground. According to the installation manual for a Midland Model 4001 CB radio, the unit is designed for 12-volt, negative ground systems only, and “some newer large trucks may have a positive ground.” The manual makes clear what you probably already know: If the minus (-) battery cable is connected to the engine block, the truck has a negative ground system. Check with your truck dealer if you can’t determine the polarity of the system.

Make sure your truck has a 12-volt system (not 24). If it has a positive ground system, you can purchase a CB designed for either type of polarity.

Mounting the unit
“Every CB comes with a bracket for mounting on the dash or in a cubby hole,” Sandoval says. “There will be a simple diagram to show you how to do that. You can also call our customer service line for help, if you need it.”

The manual for installing the Midland 4001 CB, for example, has some important advice about deciding where to install your CB: “Be sure that the unit is located so that it does not interfere with the driver, supplemental restraint systems (air bags) or impair access to any controls. Connecting cables must be routed and secured in such a manner as not to interfere with the operation of the brake, accelerator or other controls.” Although most trucks don’t have airbags, a few do, so recognize that possibility and ensure clearance accordingly.

Route everything carefully, use durable ties to keep cables in place, and then sit in the driver’s seat and make sure there is clearance everywhere around you – including your feet – before driving the truck. Make sure the front seat passenger won’t run into trouble, either.

Most units have a mounting bracket that makes it easy for you to attach it to the underside of the dash or anywhere else you want. The radio itself then attaches to the bracket at any angle you want.

  1. Attach the unit to the bracket, via the slide or hinge mechanism and knobs normally used, before installing the bracket. Then position the bracket on the dash or wherever you plan to mount it to make sure there is clearance for you when driving and that you can reach the controls. Brackets normally are attached with short machine or sheet metal screws, a type of screw that makes its own threads when a small hole is drilled through the metal first. Before starting the drilling, eyeball the length of the screws to make sure you have a good idea how far they will penetrate into the metal. Then check behind the metal panel where you will be mounting the unit to make sure there is plenty of clearance for the screws to go through without running into anything mounted there or damaging wiring or other components.

  2. Disconnect the unit from the bracket. Get an awl or sharp nail, and then position the bracket exactly where it will be when the unit is installed. When you are sure the bracket is in just the right place, hold it securely and stick the awl or nail through each of the mounting holes to mark exactly where they will go on the metal surface.
  3. Now you will need a drill that is slightly smaller than the diameter of the machine screws used for mounting. On Midland CBs, that means a drill that will make a 1/8-inch hole. Carefully drill holes right where your marks are so you can easily get the screws started in the metal. This will be easier to do right if you either use a hand drill and turn it slowly or use an electric drill that you can turn down to a low rpm. Be careful not to allow the drill to penetrate very far through the metal unless you know there is plenty of clearance.
  4. Finally, put the bracket in position. Take a minute to pick out exactly the right size and style of screwdriver for the screws because this will help make it easy to put enough torque on them without damaging the heads. Then install and snug up all the mounting screws.

Connecting the power wiring
On the Midland CB, connect the polarized power plug to the rear of the radio. If your radio has a similar, plug-in connector, connect it now.

Now you have to decide where to hook up your radio for power. Sandoval suggests that it is ideal, from the standpoint of ensuring maximum voltage, to connect your radio directly to the battery terminals. However, there are two problems with connecting there. First, you would probably need to get a power cord that is longer than the one provided with your radio. Second, you will always need to remember to turn off the radio when you shut down the vehicle as it will be powered up at all times.

An excellent compromise is to connect the wiring to the accessory junction box, which is something “most trucks have,” according to Sandoval. This is a spot where good voltage is guaranteed, polarity is marked and the radio will be shut down when you shut down the truck. Locations vary. If you can’t find this, ask your dealer whether or not your truck has one and how to find it if it does. Older trucks may have two simple terminals for accessories somewhere on or under the dash.

It’s best to disconnect the negative battery cable now and leave it disconnected while you are connecting the unit’s power wiring. This way, if you were to create a short circuit as you work, it would not cause damage.

The positive side of the power cord will have a fuse in it to protect the unit and the truck’s wiring in case of a short. It will also be red if the wires are color-coded, as on units from Midland and Uniden. On Midland CBs, you can connect this to the accessory terminal on the fuse block or ignition switch, so that your CB automatically goes off when the ignition goes off. Then tightly connect the ground (black wire) directly to the vehicle’s metal frame. A good direct metal-to-metal ground is essential for optimum performance.

On other CBs, which typically can be installed on either positive or negative ground systems, make sure you know which type of polarity you have. Positive ground systems will have the red battery connectors, normally marked on the battery with a plus sign, connected to the alternator and starter, while the negative connection will go to the engine block. Positive ground systems will have a connection between the battery positive terminal and the engine block, while the negative terminal will connect to the alternator and starter.

With the more typical negative ground systems, connect the (typically) red lead from the CB with the fuse in it to the positive battery terminal or red, positive connector in the accessory junction box. Connect the negative lead to the negative battery terminal or negative connector in the accessory junction box. You could also connect the positive lead to an accessory connector in the fuse box or the battery side of a fuse. If connecting to a circuit in the fuse box, find one that turns off with the ignition switch. The negative lead to the CB must then be tightly connected to a good chassis ground, ideally the frame, or to a negative accessory connector in the fuse box, if one is provided.

With positive ground, connect the red lead with the fuse to the vehicle chassis or battery positive terminal, or to a positive terminal in the accessory junction box. Connect the negative, black lead to the negative battery terminal, or to a negative terminal in the accessory junction box.

Once your wiring is secure, reconnect the battery terminal.

The aerial
The most important part of the CB radio system is the antenna, Sandoval says. “If you choose a good antenna, you get good performance. If not, you get mediocre performance,” he says. “Also, the longer the antenna whip, the better.”

The installation manual for the Uniden PC68 CB radio says, “Because the maximum power output of your transmitter is limited by the FCC, the quality of your antenna is very important. Only a properly matched antenna system will allow maximum power transfer from the 50-ohm transmission line to the radiating element (antenna).”

The manual recommends that you don’t skimp when buying the antenna and that you seek the advice of the dealer who sold you the CB. It also recommends a longer style antenna, termed a full “quarter wave” device.

The Midland manual states that mounted height above the roof helps the antenna to transmit more efficiently.

“But consider the installed height,” Sandoval says. The antenna needs to be set so the top is at a height near where the top of your trailer or load would be, so it will clear bridges. While an occasional gentle rub on a tree branch probably won’t hurt it, constant hard collisions with bridges will make short work of a valuable antenna.

The Midland manual says the antenna must be mounted so it will be eight inches or more from anybody riding in or driving the truck; it must also be mounted well away from any other antenna. And by the way, never try to transmit with the CB unless the antenna is connected and the cable is intact.

When it comes to mounting, “The most important thing is that the antenna mounting system must be properly grounded to the chassis,” Sandoval says. The chassis then becomes a part of the system and helps the signal come out of the antenna evenly.

“Make sure the antenna bracket is in contact with the mirror bracket and that there is continuity from there right back to the frame,” Sandoval says. This means ensuring metal-to-metal contact with the mirror bracket – no interfering rust or plastic or rubber mounting parts. Also, it would be helpful to check the condition of any ground straps connecting the cab to the chassis and make sure connections are clean and tight.

Carefully inspect where a fiberglass whip antenna mounts to its metal mounting bracket. Sandoval says there’s a nylon bushing where the antenna-mounting stud connects the antenna (through female threads) to that bracket. “The bushing needs to be there to separate the antenna mounting stud from the bracket,” he says. If the part is missing, ask the antenna supplier for a replacement.

If you mount “co-phase” (dual antennae) to the mirror brackets, the cable going back to the CB will form a Y where the leads from the two antennae connect. “When routing the cable back, you do not want that to touch any other cables in the vehicle like the one carrying the stereo signal to the speakers,” Sandoval says. You need to “isolate the cables from the other electronics in the vehicle.”

Also, routing is critical if there is excess cable. The last thing you want is a ball or coil of cable in one spot because that will create tremendous resistance. “Route it around the cab so it’s stretched out,” Sandoval says.

The cable is then routed to the back of the radio and connected.


Routine Maintenance
The manual for the Uniden PC68 recommends having the SWR adjusted every six months (or doing it yourself). They also recommend a careful inspection to make sure mounting hardware and electrical connections are tight. Inspect the coaxial cable to the antenna along its entire length to make sure it’s not worn and that the shielding is intact everywhere. Replace if necessary.

Take care to follow these points during installation so the radio will get good voltage and the signal will be properly protected and distributed. A little extra care now will give you many happy hours of communication with your fellow drivers down the road.


Adjusting the SWR
“SWR” means “standing wave ratio.” This involves tuning the antenna and the CB to one another. It involves adjusting the CB itself and then tuning the exact length of the antenna to the characteristics of the CB. The tuning must be done in both Channel 1 and Channel 40; and, with dual antennae, it must be done for each antenna.

Some CBs are equipped with an internal SWR meter, but an external one can easily be used if yours is not so equipped. This is a difficult operation for someone unfamiliar with electronics, but it can be easily accomplished by a technician where you purchased your equipment. If you’re comfortable with electronics, you can normally find the steps included with the directions for installing the antenna and can probably do it yourself.


For further information
Cobra Electronics
www.cobra.com
(773) 889-3087

Midland Radio Corp.
www.midlandradio.com
(816) 241 8500

Uniden America Corp.
www.uniden.com
(800) 858-3300

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