I bought some CB antennas with mirror mounts and 18 ft. of cable. Can I cut the cable and reconnect it? The connector(s) at 9' and 18' feet will be a real %@#*! to feed through some holes. Solder/shrink wrap good enough?

Thanks,
Dan

P.S. the mirror mounts suck! They won't fit on the towing mirrors of my 00 F-350!!! The mirror 'struts' are too fat. Anybody know where I can get just the mounts for a 4' fiberglass cable?

 

Cutting them should not be a problem. You are not running enough power for varying lengths to be a problem (I'm assuming you are running legal.) In my eyes, soldering connectors is the only way to do it for a good connection. Biggest thing to be careful of is inadvertantly shorting the line when you put the connector on. (Sometimes, part of the ground braid finds it's way to the center conductor.)

 

You didn't say if the antennas you bought were "ground independent" or not. If they are, then DON'T CUT THE CABLE. This will destroy the SWR match. A ground independent antenna doesn't need a ground connection at the antenna mount to match properly. It relies on a specific length of feedline (coax) to match properly. If you don't have this kind of antenna, then by all means, cut away. Just be careful to solder the connector or mount end back on good. Some of the premade connectors are real bad, so soldering on a new one is quite often an improvement.

 

NO NO NO, you can't just solder/heat-shrink coax! Coax is constant-impedence... if you cut it, you need to install mating connectors and connect them... not just try to solder the center and shield together.

NFG has it right about the possibility of a required specific feedline length.

 

Coax has to be used in multiples of 3', example 3' 6' 9' 12' 18' 21' are the most common sizes I use at work, Craig.

 

I tell you what... it's damn difficult getting the yellow tape out and measuring the Heliax running up a tower to make sure we've got a multiple of three feet.

Coax does NOT have to be used in multiples of 3'. The only time coax length matters is, for instance, on a few special types of antennas, and also on duplexer jumpers, etc.

My F-350 has a total of 20 runs of Belden RG-58A/U and Times Microwave LMR-195 to handle the radio equipment being installed within. I've been working with radio for ~15 years. I think I should know what I'm talking about...

 

If you are running a co-phase harness, then both sides have to be the same length, whatever that may be, right?

 

How do I tell if they are "ground-independant" antennas? Is there a way to tell by looking at it? All I know is that they have aluminum brackets that bolt to the mirror arm. I need to cut cable, I can't get around it! The connectors are too big! Even if this is a ground independant or a non ground independant antenna, the cable needs to be cut. Can't I just cut them and put new connectors on? I think the antennas are "Work Boy" or something like that, can't find a website on them. I bought them off of ebay so I can't go ask somebody at a store. The seller I bought it from knows nothing about them. I am running a co-phase harness, where both sides are equal.

Thanks,
DC-9

 

If you're running co-phased antennas on a Super Duty, you're an idiot. Sorry, but it's true.

The idea of phasing a pair of antennas is to provide omnidirectional coverage on an 18-wheeler. A tractor-trailer rig will often stick the trailer behind the antenna should it be mounted on one side. If you look at the response on an azimuth plot, you'll see a large null where the trailer is (obvious). The purpose of phasing antennas is to install an antenna on the opposite side as well to eliminate the null and generate coverage approaching omni.

If the antennas can see each other (physically) then you're only adding the insertion loss from the phasing harness and opening up the potential for problems.

 

Not true.

I have never seen an 18 wheeler where the dual antennas could NOT physically see each other, thats almost physically impossible. I mounted dual wilson silverloads on each side of my tool box, tuned them and have gotten my SWR to about 1.1-1.3. What kind of problems are you talking about? Ive been running them like this on a Grant XL for about 10 years, have had no problems TX or RX.

9' is the magic number, when you get to about 5-6' or closer, you run into tuning problems, but they can be overcome. You won't get omni directional pattern, but you will gain most of the benefits of having a cophased system. If they are tuned properly, NO HARM will come of it. Besides that, when you are on the road, the front and back is where i want my TX and RX power, so the sides are not of the most importance.

 

Try not to get hung up on what Redneck Bob at your local CB shop or truckstop says. Most of these guys are giving you nothing but personal oppinion. Take all the advice, and then read up a little bit in books or reputable websites and you will reach a good decision.

 

What exactly do you see as the benefits of phasing a pair of antennas? If they can physically see each other, you get no better radiation pattern... you have a whole new set of problems to work with... you have the insertion loss of the phasing harness... lots of cons, not many pros (other than it looks redneck-sexy). Sure, you might be able to make it work with no problems (although I'd venture to say you don't have the test equipment to say this with certainty) but are you getting any benefit out of it?

When we phase antennas, we do it on a tower with the antennas stacked vertically using commercial hardware and dB's phasing harness, for the purpose of increasing gain or playing with the coverage pattern. You can't see the benefits of increased gain if the antennas are in the same vertical plane.

Of course, I've had this argument with other CBer types... most seem to think that the advice they've heard from Billyfred down the street changes the laws of physics.

As for me, a simple Radiall/Larsen NMO27 mounted on a lip mount just works... nice omnidirectional pattern, virtually zero SWR, etc. I think you'd be surprised what you might see if you plugged a Sitemaster into your phased whoop-aerials.

 

thats what i am asking....

Where have you ever seen an 18 wheeler with phased antennas situated such that they cannot physically see each other? Its not possible unless one is mounted on the mirror and one is mounted on the running boards.

I cannot speak to the physics of it, but i can speak to the operation. I have personally never noticed any difference between a cophased system vs. a non-cophased system for my application. For my radio setup, neither system shows an advantage over the other. It may be true in theory, but theory and practice are often very different.

Also, please explain insertion loss...

 

Insertion loss is loss introduced by a system... in this case, the phasing harness. You're going to lose a dB or two, especially if the harness is connectorized.

I'm not saying I agree with the 18-wheeler systems either. Just like I don't agree with most of the CB droids running a killer-watt linneyor.

You don't need phased antennas on a Super Duty, of any description.

 

Drop all that junk, buy a Wilson Mag mount antenna, run the cable out the cab vents in the rear of the truck, tune to SWR and have a nice day.