Does anyone know how i can get a good ground to my cb antenna. It is set up through the bed. right behing my sliding rear window. do i jus run a wire (ground) from my fram to the antenna? Just not getting good ground. Any help would be great guys!

 

When i was going to mount a mountable antenna on my metal that i put on my bed, since the bed is fiberglass i was going to run a ground to the piece of metal.....i thought you had it mounted on your bumper now??

Rocky

 

did but not working there. so i put the whip up on the bed rail centerd with the sliding rear window. Its weird because i m rinning the same set up as b4 but with one antenna (same mounting procedures) and i get nothing. hmmmmmmm

 

Wait a minuete, what antenna are u using now?

 

The steel bed is a ground. You don't need to go to the frame.

 

my guess would be to use a ground wire. but it didnt make sense that when the ground wire was on nothing, but then we took the wire off we got ppl talkin. weird.

 

The shield of the coax gets grounded to the antenna mount. Do not try to attach it anywhere else. The mount is attached to the steel bed therefore it is grounded.

The center conductor of the coax is attached to the center pin of the antenna mount. The center pin and the shield/ground must not be touching eachother.

 

69" stainless steel whip. Its a trucker 2000 antenna. Just running 1 now. Like the way the whip looks.

 

Right. Thats why i have this black plastic circular piece on the bottom side of the antenna bracket so it does not touch the bracket causing it to touch ground. I checked all my connections and they were tight and nothing wrong with them. Now could it be that i have a dual coax line coming out (from when i was runnings dual fiberglass whips) and im only using one now? should i just get one coax to run strait from the cb to the antenna since i dont use 2 antennas any more?

 

DOH! Yes. Definately. Get rid of that co-phase harness. You want one piece of coax going from the antenna to the radio.

 

lol didnt think i would need jus a single one. lol I guess that would help or no?

 

how many feet will work? i only saw 5',9', and 18'

 

Lesson #1 in coaxial cable. For a single antenna installation, the optimum length of coax is the shortest run possible. The BS about "Optimum 18ft of coax" is a myth that just refuses to die. There is no length requirement for a single antenna installation.

 

so if i get the 18' ill be ok than. i even if (prob will) have extra?

 

if you have extra, do not coil it up in a ball. Spread it out. Ideally, you should cut it down to the proper length so there is enough to go from point A to point B with a little bit of slack to work with.

 

so pretty much hes saying that u should go with the 9' and be happy. hey shane u doin this 2 nite?

 

yeah stopping by the truck stop tonight. I got to measure it first. idk if 9' will be long enough...........it went from 9' to 18' i saw

 

ok ill have to go measure now to see bout how much ill need. well on my lunch break.

 

get 18'...9' isnt enough, it might be just to run it inside the door but not if you will ever move it...where i have my mount its bolted to fiberglass so a whip would need grounded....Thats why i want to stick with a manget mount, hopefully ill be getting my wilson 1000 magnet mount soon..

Rocky

 

ok ill jus get the 18' then. I have to ground the antenna tho cause when i took a ground wire to my frame to the antenna it picked up reception and when i too it off nothing. I got to fing a good way to connect the wire tho.

 

Yes, and no, Matt.

You will occasionally use a length that causes an antenna to not tune. The actual length required is a EVEN multiple of 1/4 wavelength (1/4 wave is 8 to 9 feet at CB frequencies). This is NOT a myth.

Every 1/4 wave, the line acts as an "impedance" transformer. It reverses the relationship between voltage and current (not the phase: instead it causes a change to a different impedance, changing the ratio between voltage and current, although the two together still multiply out to the same power).

Here's some info on it, if you'd care to wade through it, lol.

http://www.firecommunications.com/coax.shtml

Anyway, if you use 1/4 wave of coax, you'll have a nasty time getting a match from your antenna, and it even if you match, it will tend to be "high Q" and narrow -- it will be out rapidly as you change frequency.

So, the 18 feet is a real usefu number. You should either be about 6 feet or less, or in the 14 to 22 foot range to keep from getting too close to an "odd multiple" of 1/4 wave.

Cut some line sometimes and you'll see what I mean, lol.

Actually, 18 feet may not be right either. There's a thing called velocity factor that figures in. Since waves move slower down a coax than they do in free space, a 1/4 wave section of coax is shorter than the "reference" 1/4 wave length in free space. Well, that's for advanced students, lol!

Anyway, keep to to an approximate even number of 1/4 wavelengths and matching will be easier.

 

In all the professional emergency services communications work I have done myself or have seen done from the many communications service companies (ie- Motorola, Kenwood, etc), never once has a piece of coax been measured. I'm not denying what you are saying, you clearly have a lot more RF theory and nitty-gritty than I do. I'm more of a programming and physical installation guy. Now that you've meantioned it, I'm going to ask some of the guys at the radio shop about this to see what they have to say.

Either way, it does not *need* to be 18ft or 9ft.

 

but i do need a single coax right?

 

9 feet is bad, lol.

Well, you're right: some professionals don't keep track of cable. And guess what? I have a friend who has made a great deal of money fixing bad installations with incorrect cable lengths, lol. The WORK, yes -- but they don't work with full efficiency. REAL professionals are aware of this and either precut the cable, or cut it after installation if there are problems.

By the way, if the feed line is long enough, the loss over the long cable MASKS the impedance mismatch when measured from the transmitter end -- but you would see it if you're at the antenna.

Here's something to try with your 2 meter rig. Put an SWR meter on your rig, and measure/set the SWR on your antenna. Now, add an additional 14" to 18" jumper between the SWR meter and the antenna and measure it again. What do you see? Do NOT put it between the transmitter and meter, lol, or you won't be measuring the result -- only the transmitter will see it.

This will be on the test, lol...quiz on Friday.

 

so a jumper with a single coax?