Don’t Cheapen Out the System and Certain Truck Issues
Anything that has a CB in it, from an ATV to a Tractomas and everything in between, your CB setup is a “system”. You can buy a huge radio, but if you go cheap on the rest and wonder why you only get out a mile, it’s because you’re a cheap bastard! Everybody has their favorite brand and sometimes it’s based on what your daddy ran or going against your pop (please see other publications of why you do shit). What I am going to present of how to get out there better based on real world practice. I have run software and performed the calculations the old fashion way and have proven one thing. Getting a mobile antenna to perform EFFICIENTLY is almost freakin impossible!
A lot of drivers, tri-axles especially, want the shortest antenna possible because they’re always in low laying shit. I get that, but what you are putting out power wise on a 1 foot antenna is hideous! Now it’s just plain old physics that the manufactures have to get any antenna to act like it’s 102” long. They wind it, twist it, make big coils, tiny ones, open air, totally sealed (which sometimes let water in), oil filled, base loaded, center loaded, top loaded. Hell, I took a short antenna apart and it had 28’ of wire, a coil on a coil. It will be tunable, and you can get the SWR down, but it ain’t doing it efficiently! As a matter of fact, after you look at the chart below, you will either tell me I’m full of shit or you’ll go “oh shit”.
| Antenna Length | Efficiency | 10 watts in gives you |
| 12” | 0.6% | 0.06 watts output |
| 24” | 2.4% | 0.24 watts out |
| 36” | 5.3% | 0.53 watts out |
| 48 | 9.5% | 0.95 watts out |
| 53” | 11.6% | 1.16 watts out |
| 60” | 15.3% | 1.53 watts out |
| 64” | 17% | 1.7 watts out |
Some of you might be saying how is this possible. You have your SWRs perfect based on any meter you put on it. Well, when you bring your radio to a shop, they hook it up to a 1.1:1 SWR dummy load, a perfect match that is a few inches long and does not radiate. Where does all that power go? It gets transformed into heat! Yup, your 10 watt output radio on a 1 foot antenna makes 9.94 watts of heat, farking heat! That is as efficient as shoveling out a dump trailer with a trowel. Get a bigger radio and you will be able to toast your bagel in the morning. To add insult to injury, the numbers above are the best-case scenario. Also, I’m using 10 watts to make the math simpler. Smaller radio, smaller output and you ain’t talking outside of the yard.
You may be wondering how these figures were calculated. Like I said, I crunched them with a calculator, not the one on your phone, an old TI 80 something. I had to make assumptions which bothered the shit out of me, but some things are not measurable. The big one is ground resistance. So my next adventure was software which is really phenomenal but again assumptions had to be made. When I used the best possible parameters, the program matched up with the pages of calculations I had, BUT, it was under the best possible conditions that don’t exist. For example, it’s all based on the antenna being in “free space”. Well, it happens to be attached to a truck, so that one is out. Ground resistance, yeah, anywhere between 6 to 26 ohms. That kind of range is like comparing sleeping overnight in a two stick, one stack Mack with a window in the back versus an 86” sleeper, it just doesn’t compare. All you Mack folk please take note, the only thing I mentioned is sleeping in it, so ease up on the hate mail.
So, being the nurd that I am, I had to take it to the next level and do actual testing. I took a walkie-talkie, turned down the output to a consistent 1 watt. It was then wired it directly to the aforementioned antennas tuned to 27.185 to the lowest SWR and resonant. I used a field strength meter at a measured distance. Now this is not an exact measurement of power, but a relative comparison of power between antennas. And holy shit, the numbers correlated. Same truck, same antenna placement, same power output and where the strength meter max out on a 64” antenna, it barely moved on a 12”! You can have the lowest SRW possible, but it has nothing to do with efficiency! Size matters. Also, I’d like to thank all those who let me use their trucks in the process, I owe you all a beer.
Specific Issues with Specific Trucks.
Before I get into specifics, if you run your coax through the door and it’s constantly getting mashed, contact me. I have a down-n-dirty method to prevent this from happening again and you will no longer have an excuse of why you didn’t replace the coax yearly besides the fact that you have CRS.
Peterbilt pre 2006 300 Series Cab with Mirror Mounted Antennas
(359, 379, 352, 362, 377, 357, 378, 389, etc)
Sloppy door hinges that lead to a bad ground. I have come by this issue so much that it’s worth mentioning. Solution, a short, let me repeat, short ground strap from the door to the door frame. This bonding usually takes care of an untunable antenna. Hint that this is occurring – can’t get theSWRs below 2.
Peterbilt post 2006 300 Series – your mirrors are
cab mounted and 99.5% of the time there is no issue.
New Western Star 4900
The bullet proof plastic mirror frames are plastic. When the antenna is screwed into the mirror it’s mounted in plastic so there is no ground. The mirror needs to be bonded.
Mack: Anthem and Pinnacle
The mirrors are metal, but they are mounted in rubber isolators. A short bonding strap from the mirror mounting screws to a stainless antenna bracket will usually do the trick.
T600 series
The single aluminum mirror arm can corrode up like a mofo. On a recent installation I had to hammer the stud out of the arm! When doing an install, I have a cart and tool belt to minimize trips up the ladder or back into the shop. I’m a radio guy so there is no hammer, never had a use for one to install an antenna until now. Clean the crap out of it. It’s a pain in the ass but sand every little bit of aluminum oxide off and out of the mounting hole and replace the stud at least once a year.
"To those who fight for it, life has a flavor the protected never know."