Warning: New Trucks with Bad Coax!

Pretty well-known about the new trucks having junk coax. And don't get me started on those stupid multiplexers. At least the ProStar coax goes straight from the CB to the antenna(s), unlike, well, every other truck on the market now.

 

Yeah I get that.

And in the ProStar, if it has twin antennas, instead of a proper co-phase harness, it's spliced RG-58...and the runs are of unequal length. Yikes...

 

I don't know, I just bought a second brand new truck - Mack - and it has Belden coax. Ripping it out doesn't make much sense especially when the losses according to my little HP transmission line test thingy shows less losses with this new truck than my pickup truck's Scorpion antenna. I put in a Cobra 29XLR in the truck an talked to my wife 18 miles form me until she got to the storage yard, the radio was tuned up to factory specs by the way.

 

Unsurprising, considering Mack's primary customer base. Lots of Mack dump trucks, and those guys are often required to have a CB in good working order.

Freightliner couldn't care less, and it shows.

 

Once your radio is hooked up, The very first thing to do is check the SWR with an external meter. Do not run your mouth on the CB radio until you have a SWR reading below 3. Why?
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.Because a reading of 3 or higher on an external SWR meter can cause the final amplification circuit to degrade and damage your radio. What you think is being transmitted is mostly being reflected back to the radio and beating up your amplification circuit or "finals". This circuit will degrade to an absence of an final amplifiction of your signal. Without being amplified, your radio will work across the truckstop parking lot [maybe] but not be worth spit on the road.
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.There are 3 possible causes: A- bad coax, B- bad antenna or C- bad or faulty antenna ground. For both A&B the solution is simple. If you can borrow from a friend a section of known good coax of the proper resistance and a known good antenna, one at a time, substitute a known good component and recheck your SWR. If necessary substitute the other possibility with a known good component and, again, recheck your SWR with an external meter.
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.If neither the coax nor antenna is the problem, that leaves the antenna ground plane as the only possible solution. Do a search on "Antenna Ground Plane" in this the CB radio forum. This has been covered to death in great detail.

 

A couple few things that come to mind about this subject.

First thing is how does someone test coax in the CB world? I mean that unless there is access to a few pieces of equipment like say a TDR or a VNA, then how?A continuity test isn't showing degrading dielectric issues within the coax.

The second thing is how does one determine other than putting grounds everywhere to produce an RF ground?

As for the SWR meter, I've had a few bad ones in the past, even a bird slug that gave far off readings on low (reflective) power. The best one was a Lafayette meter that was built in kit form in 1968, it seems to be the best one yet other than the antenna analyser, Diawa, HP and military meters. So how does one know when they are bad?

 

Would a dipole setup not solve this issue?

 

Over the years some of the best performing radios have been stock right out of the box with no modifications using factory coaxial cable on a brand new truck with factory antennas. The guys that seem to have most of the problems are the ones that spend big money for big radios and big fancy antennas from radio technicians that don't have a clue what they are doing. I agree on plastic trucks like Kenworth t2000 and Peterbilt 387 the factory antenna system leaves much to be desired but I have never encountered a direct short in a brand new piece of cable.