Need help routing coax in Volvo

why 18 feet? the only coax you need is enough to run from the radio to the antenna. the 18 foot or 3 foot increments is false.

 

Why 18 foot?

 

if you think the 18 foot myth is real, perhaps you need to sit down and read this link.

http://www.stu-offroad.com/misc/myth-1.htm

 

Volt -- you're the one who made the point initially about having a handmade 18-foot lead, then you asked how to route it. I think that exposing the myth (again, as have others) is a valid point.
As for routing it without pinching it, what size coax did you get? For as short a lead as you need from average mounting location for a radio in a tractor cab to an average antenna mounting point, there's absolutely no need for anything larger than RG-58A/U (0.20 inch). If you used something larger, like RG-8x, you gain outside diameter (about 0.25 inch) with exactly zero additional performance at 27 MHz.
Sure, with better gear than most shops have, you might be able to measure a nearly infinitesimally greater amount of signal out to the antenna (or in to the receiver), but it will never be noted on the air.

Unless your door-edge to fender gap is under 0.20 inches, RG-58A/U won't get pinched. If you can't drill any holes, and since passivated glass windows don't pass RF well enough to work with an on-glass antenna, you're severely limited in your transmission line choices.

Personally, I'd be looking for a spare rubber grommet in the firewall, then go up to the fender where the hood closes (unless you're in a cabover).

But RG-58A/U should fit through nearly any "natural" opening between movable door panels.

By the way, simply having a chunk of coax handmade at a shop doesn't guarantee its quality. There are a few different methods of a soldered connection, some of which melt the inner insulation on the coax, altering the inter-conductor spacing, forming an "impedance lump", although again, at just 27 MHz, anything less than a dead short will hardly be noticed.

Since I'm used to working on gear that runs up to nearly 2 GHz in frequency, I typically sweep all my cables with a TDR (Time Domain Reflectometer -- and no, neither Radio Shack nor Dosy build them). So I'm a purist, but the principles hold true -- as does a random length of coax that has the same characteristic impedance as the source and the load.

73

 

RG-8? The half inch thick cable? That's base station stuff for when you are running 100' or more. Good luck running that.

 

If you can find another use for the RG-8 you've got, you could use RG-58-class coax and lose only about 0.15 dB for 10 feet at 27 MHz (if that'll reach) and handle up to 900 watts, all at just 0.20 inches outside diameter. It's what I use for most VHF & UHF installations in some of the most demanding uses -- police, fire, and EMS vehicles -- and seldom have to replace the coax run. The only time I do is when I'm removing a radio installation from one vehicle and putting it in another vehicle, and I do so to avoid any chance of scraping the outer jacket from the coax. It's worth $10 or $12 for another cable kit and NMO mount (which i use for nearly all my installations).

Just a thought, especially as you may have no other recourse for routing the big stuff.

As always, I hope it helps -- and MsJ has a good point above, too.
73