Truck cabs are sprouting an increasing number of antennas. Ideally, a CB antenna should be mounted at least 30 inches from others.
Combination wrench set
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Karl’s CB Shop
Walcott CB Sales
An antenna is to a citizens band radio what a transmission is to an engine: It transfers power from its source to some useful destination. Unfortunately, many truckers are using antennas that function as if they were missing the top three gears.
Several problems afflict antenna performance. Truck cabs and sleepers are increasingly made from composite materials, which provide no ground plane, an essential element for most CB operations. Manufacturers are outfitting their trucks with multi-purpose antennas designed to receive a wide range of airwaves. And a growing number of truckers no longer understand the fundamentals of CB equipment or perform the necessary maintenance.
CB customers were well-versed in the 1970s, says Rick Vincent, owner of Firestik Antenna Co. in Phoenix. “They’d be asking us about propagation philosophies, angles of radiation, impedance and inductance,” he says. “Now, a lot of people don’t know even the basics of antennas or the required tuning. I call this the Microsoft syndrome: Everyone has become too accustomed to point-and-click technology.”
Changes in CB distribution have also contributed to this decline in customer knowledge, says Bob Gladden, vice president of sales at Omnitronics in Cleveland. The CB shops of yesteryear “are somewhat of a dying breed,” he says. They’ve been replaced by large electronics stores, truck stops and Internet merchants, all of which can offer competitive pricing, but fall short when it comes to discussing the subtle nuances of gain, co-phase and voltage standing wave ratios.
Of course, these terms interested truckers more 30 years ago, when CBs were the only communication devices they had. Today, the humble, 4-watt two-ways must share time and cab space with cell phones, satellite messaging units, Internet-connected laptops and digital pagers. Still, the CB provides drivers with unlimited, free airtime and information available nowhere else on the electromagnetic spectrum. Given the device’s utility – and meager legal power limit – its optimum performance is essential to anyone wanting to “ratchet-jaw” with others more than 50 feet away. There are several procedures for ensuring maximum output.
TUNE THE RADIO. A CB radio is only as good as the coax and antenna connected to it. However, the unit itself should be tuned occasionally by a reliable technician. This procedure, known as a peak and tweak, is particularly important for new radios, which are intentionally detuned at the factory.
“Most manufacturers set their radios just below 4 watts,” says Firestik’s Vincent. “All of these products are made overseas. If the FCC checked an incoming shipment and found a couple of units putting out more than the allowable power, the agency would seize the entire shipment and require the manufacturer to recalibrate every unit.”
Peak-and-tweak services vary by shop, says Peter Toher, a technician at Walcott CB Sales in Walcott, Iowa. “I’ve seen some guys go in and just clip the modulation limiter and call it good,” he says. “Others take their time and go through the receive, gain and squelch; then they’ll do a frequency count and adjust modulation and power.” Toher says that most radios are capable of delivering much more than the standard-issue wattage, even without a linear amplifier. The key to maximizing output is finding a trustworthy shop staffed with skilled technicians.
The same shop can also offer helpful advice on choosing and installing the best-performing coax and antennas. These recommendations, though, might differ from those of other shops.
For example, some say that dual antennas work better than a single or that fiberglass is better than steel. Others say just the opposite. Some tout the benefits of top-loaded antennas, while others make similar cases for center- and base-loaded models. Many claim that coax must always be 18 feet long (or 36 feet for dual), but a few say that coax length is unimportant. At least three remedies exist for handling excess coax: A. Wind it in random-sized loops, secured with wire ties. B. Just stuff it into the headliner without ties. C. Route it through the cab along an indirect path that takes up the extra length.
USE CB-SPECIFIC ANTENNAS. Luckily for bewildered consumers, there is nearly universal consensus on other CB topics, such as the need for a good ground plane and regular CB maintenance, the importance of a low VSWR (voltage standing wave ratio) reading, and the pitfalls of factory-installed antennas and coax.
“What a nightmare,” says Vincent at Firestik. “Not only are truck makers using cheap coax, but they’re combining the antenna and coax function to serve all of a cab’s radios. This was done more for the convenience of manufacturing than radio performance. The CB always suffers.”
Mark Pili at Karl’s CB Shop in Las Vegas, agrees. “When you use the same antenna to collect multiple frequencies, there’s always a chance of bleed-over,” he says. “At least one of the radios won’t perform as well as it should.”
This problem can easily be remedied by switching to an antenna designed solely for CB signals. In doing so, however, you should mount it at least 30 inches – and preferably more – from the truck’s other antennas to reduce possible interference.
ESTABLISH A GROUND PLANE. Ramon Sandoval, a product manager at Cobra Electronics, says multi-purpose antennas are just one of several problems involving factory-installed equipment. He contends that the placement of antenna mounts and lack of a ground plane are equally troublesome. Truck makers “don’t really care about this stuff,” he says. “The installation of antenna brackets is the least of their concerns. In the past, some manufacturers didn’t even know that antennas needed to be grounded.”
All loaded antennas – that is, those with copper winding inside – must have a ground plane to work properly. A ground plane allows radio signals, which are electrical in nature, to flow between an antenna and receiver. This type of ground is achieved when an antenna bracket is mounted on a metal mirror brace, which is attached to a metal door or frame. If the mirror brace is made of a non-conducting material, the ground plane must be built, using a short length of braided metal strap to connect the antenna bracket to a nearby hinge or some other substantial metal part. A lot of truckers have mistakenly run a single long wire from their antenna to a negative battery post. This doesn’t work, though, because batteries operate on a DC, not RF, ground.
A poor ground plane is visibly evident in a VSWR check, registering a 3:1 ratio (or more) across all channels. To verify this type of trouble, technicians will sometimes grab an antenna to create a ground plane with their bodies. The action will decrease the ratio if the original ground had been faulty.
CHECK THE VSWR. Periodic VSWR checks are important because they indicate how much outgoing power is being returned to the radio. A ratio between 1.3:1 and 1.5:1 is considered ideal. The suggested limit is 2:1. Beyond that, too much power is being fed back into the radio’s output transistors, called finals, causing them to heat up and, eventually, burn out.
Measuring VSWR (called viswar) requires only a meter and short piece of coax with a PL-259 connector at each end. The antenna’s coax should be connected to the meter, and the jumper coax between the meter and radio. Meters vary by model, and each comes with its own set of operating instructions. VSWR is typically measured on three channels: 1, 19 and 40. If the ratio is greater on 40 than on 1, the antenna is too long. If the opposite is true, the antenna is too short. Many antennas on the market today can be lengthened or shortened by adjusting a small metal tip at the top. Without this feature, antennas must be uncapped to expose a small wire coil. The wire is then trimmed or stretched – a mere 1/8 inch at a time – as needed.
ELIMINATE RESISTANCE. Good VSWR meters are expensive, costing $80 to $150, but they offer more features and, generally, more accuracy. Regardless of their precision, meters should not remain connected during normal CB operation. “Any test equipment or in-line filter creates resistance,” says Pili at Karl’s CB Shop. “Ideally, you should have just 50 ohms of resistance at the radio – 50 at the coax and 50 at the antenna.”
Tools and doodads aren’t the only causes of in-line resistance. Quick-connect coax plugs (used by some truck makers) also contribute to the problem, says Lamont Davidson, owner of Walcott CB Sales. “Extra breaks in the coax are not good,” he says. “Coax is like a hydraulic line under pressure: any openings or weak areas will produce leaks, leading to performance loss.”
Corrosion is probably the biggest cause of in-line resistance. Davidson says coax will wick moisture and rot from the inside out. He suggests using a sealant on connections to help prevent the problem. He also says that coax and antennas will work better and longer if they’re periodically disassembled, inspected and cleaned.