Weird swr problem.

Isnt 250 watts too much for the multiplexor box, I had a Volvo a couple of years ago and was told by Volvo tech that the Rami system( thats the company that supplies it) could only handle 30 watts being run through it, however I did run a 2 pill box(2×1446) into it for about 6months and it never burned up or quit.

 

250 will NOT work in a ProStar with the stock coax! I tried a 200 watt setup and no go....Well worth the price to run new coax!

 

Forgot about box. You are right.

 

Probably still has one for the TV. I think my old ProStar had it because I could never get good range with the CB.
After installing my own antenna and coax my receive was way better on the CB too.

 

Had the same problem in a Volvo that uses a multiplexer also. I ended up just getting a new antenna mount and running its own coax to it. Fixed the problem.

 

Before you go changing out coax or antennas again, first spend $25 for a modest 50 ohm dummy load (like f'r instance from MFJ Enterprises), put that on the antenna end of the coax, and see if you see a 1:1 (or so) match. If you do, then your coax is OK. That being the case, put on the antennas again. If your radio has been through some sort of wildly inappropriate "tweak and peak", to where the radio is spewing out harmonics, then the antenna will do part of its job as a bandpass filter, and will reject the spurs and harmonics, showing as a high SWR. But that dummy load should show a 50 ohm match up to, depending upon the design, up to around 60 MHz, or 150 MHz, or even 1 GHz. While it won't radiate across a parking lot, the transmitter will see it as an "ideal antenna".

Even the most poorly equipped "CB shop" should have a dry dummy load in their test arsenal. Without one, a "tech" will spend all his time chasing down nearly-unfindable reactances, and without a decent antenna analyzer, will have to use coin tosses and waving a chicken overhead under a full moon to try to figure out whether your antenna needs a dollop of inductance (series or parallel) or capacitance (again, series or parallel) to get it resonant. Only after it's resonant should you be even considering SWR.

Remember, a perfect ground plane antenna at resonance has a feed point impedance of around 35 ohms. A resonant half-wave dipole has a feed point impedance of about 72 ohms. BOTH antennas will show an SWR of ~1.5:1.

Think about it for a minute, and you'll find that "smart" can equal "inexpensive".

HTH
73

P.S. And by all that is holy, if your truck has one of those crappy multiplexers under the dash to make one or two antennas do the job of three or four for disparate devices, just run a separate coax and antenna for your CB, as has already been suggested by many users. Multiplexers only work by attenuating (reducing) some of the energy to all ports.

 

Wow they allow you to put antennas on their trucks?

Running 250 watts with internal truck wiring?

Hate to break the news to you, and others, if you had the firestick on first and it worked great, then you put the sireo or what ever the thing is on, everything turned to crap for you - it ain't the coax.

I am betting that you messed with the actual mount or changed it out which screwed up the mount. These mounts are mass produced and some of them as simple as they are, are fragile. If you have a mid or center loaded sirioe or what ever it is, then it is a direct replacement for the firestick (3/8-24 thread) while if you have a base loaded what ever antenna thing, then you have to replace the base if I remember right and it takes a spad end on the coax (crap design). So either way I would check the mount itself, see if the insulating washers are not crushed or are messed and maybe get another one to compare.