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post #1 of (permalink) Old 09-14-2000, 07:30 AM
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Cb troubles!!

Well, my little Midland weather band cb went haywire!!.It has started making whistling noise on other cbs.It' sporattic though.I took it to the cb shop yesterday, and it checked out just fine.They said that my grounds could be bad, so I did the Cj dave thing and grounded everthing better.I switched ant. and tried to set the swr's.I cant get the swr's below 2 1/2.Just how much do you have to cut off of a metal whip to get them down? I cut it down allmost 3in. and It didnt change one bit.It isnt making the noise again yet!! but I couldnt talk to local traffic last night, or I couldnt transmit that far.I had a friend over picking up his jeep, and came in loud and clear on his radio.I had him go down the road bout 1/4 mile and he couldnt hear me.I dont know if he ever tried to get ahold of me though.His setup is a little questionable to though.Anybody out there got any smarts on this stuff?


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post #2 of (permalink) Old 09-14-2000, 08:36 AM
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Re: Cb troubles!!

Is this a magnetic antenna? Have you ever cut the cable?

Generally, a new CB antenna comes tuned to channel 1 (26.965Mhz) so depending what channel you generally use, the length will vary.

Also, when you assemble the antenna, before cutting the antenna rod, drop the rod into the antenna base until it stops then pull it up about 1/4" . This will generally tune the antenna to channel 1.

Check the SWR often. The SWR is a measure of the efficiency of the antenna.

When checking the SWR, make sure the vehicle is not near any structure (Never check SWR indoors!!). The reflection the the RF energy will be re-absorbed into the antenna giving a poor SWR ratio.

Where is the antenna placed? This makes a huge difference.

Do you have a fiberglass tub?

post #3 of (permalink) Old 09-14-2000, 08:44 AM
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Re: Cb troubles!!

The ant. is on the rear of the tub.Yes I did cut the cable to the length I needed.The ant. is going thru a big spring and diamondplate alum..It is a 6ft whip metal ant..I had a fiberglass one, but it was getting chewed up pretty good.I did just have the back of the jeep out of the garage when I was setting / trying to set the swr's.

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post #4 of (permalink) Old 09-14-2000, 10:22 AM
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Re: Cb troubles!!

When setting the SWR you should be out in an open area away from buildings. There are lots of metal in them, such as wiring, gas pipes,
water pipes and appliances. This will effect the SWR.

Gary
post #5 of (permalink) Old 09-14-2000, 10:50 AM
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Re: Cb troubles!!

Ok, but how much can a person expect to cut off a ant. to get it where you want it? The thing was shutting off the radio in my garage when I keyed it up.That good or bad?

post #6 of (permalink) Old 09-14-2000, 10:53 AM
 
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Re: Cb troubles!!

It sounds like a grounding problem at you antenna. I would check all your end connections. Also an 18 ft length of cable is optimum, as it matches the badn width of the antenna. If 18 ft is to long remove the extra in 3 ft lengths as this is fractional of the band width is will reduce impedance at the antenna and will signifacantly improve signal propogation. Again check those connections I would bet that you have a piece of the signal wire touching ground somewhere.

Jeff
89 Wrangler
I take my Jeep "On the Rocks",usually "With a Splash of Addrenalin"
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post #7 of (permalink) Old 09-14-2000, 11:31 AM
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Re: Cb troubles!!

Just because I manufacture the CBrack doesn't mean that I know much about CB radios. You would be surprised at the number of e-mails I get with radio or electronic questions. Some have even asked for obscure radio parts.

BUT, I can wade through some things sometimes.

There are some things that are important in the CB stuff. First don't get reception mixed up with transmission. It will receive long after the antenna system will not let it transmit. Second for transmitting the antena is critical from the back of the radio to the tip of the antenna. The coax length is part of that total as is the positioning and method of storing any excess coax. If you lay the coax out straight the radio works differently than if you roll the coax up in a 10" roll, for example. If you put your own ends on the coax, it has to be done perfectly. A single little strand of the outer webbed metal covering touching the wrong thing and you are out of business. Water and debris in these connections can cause problems too.

The third thing is the interference from all things electrical. Doesn't sound like that is your problem, however. Solid clean grounding is very important.

Suggestions: Get your friend back - the one with the good radio. Swap radios and try your radio with his antenna setup. If that shows your radio is good, then work your way through the system. Swap antenna with the other system and try it again. This is a rather crude method, but keep in mind, I kinda approach things from a "shade tree" perspective and not the sophisticated electronic (use meters etc) way. I suspect what you are going to find is replacing the antenna from the back of the radio to the tip of the antenna will cure your problems. The coax itself is often a cause of problems.

Doug '97 TJ
Creator of the CBrack
http://www.CBrack.com
post #8 of (permalink) Old 09-14-2000, 12:55 PM
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Re: Cb troubles!!

Make sure that you have a large enough guage wire for the CB power. If you have 22 ga. wire, that could be a cuase of this problem.

You shouldn't need to take too much off of the antenna rod, no more than 3".

If all else fails, find a local Amature Radio Operator, they are generally more than happy to help.

post #9 of (permalink) Old 09-14-2000, 01:14 PM
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Re: Cb troubles!!

I would go along with H8 on this one and guess that, if your antenna is properly mounted and the radio is ok, the problem is probably in the cut down cable. He gave the proper length advice, to which I'll add...never coil the wire. Always make one loose loop here and there to take up slack instead of cutting wire or making one big bundle. I bet if you play with the cable length, you'll find the culprit. Try just running a new cable from radio to antenna (don't bother with routing it properly..) Oh, and does the cable go past any huge sources of electronic noise (ignition, etc.)? What kind of antenna is it?

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post #10 of (permalink) Old 09-14-2000, 01:16 PM
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Re: Cb troubles!!

Hello Leader. I don't have time to walk you through the troubleshooting of your CB at this time. Today has turned into a $hit$torm.

I know more about radio than most of the folks responding. Sorry guys, but most of your advice and technical info is wrong. Not flaming anyone here, but you are wrong, and conveying it to someone who doesn't need wrong info.

You don't see 50 ohms with an ohmmeter. It is 50 ohms at frequency only. Ohmmeters test at DC. You will more likely see short or open at DC, depending on the antenna.

The length of coax doesn't matter. Period.

Yes, metal structures in the area will affect SWR, but not much. Cutting the antenna to a specific channel will affect SWR, but not much. You have described a serious problem. A little SWR problem would not cause the problems you described, and is not your problem. Something like infinite SWR would be a problem.

Look for damaged coax, bad grounds, bad connectors, or something bad with the unit. Check for good power to unit, both plus and ground.

Forget the length of coax, ohmmeters, and exact length and tuning of the antenna, and worrying about nearby metal structures. Those are things in the wrong direction.

Good luck, and I'll try to help more later.

Turtle

"Pleased to meet you, hope you guess my name."
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