merkerbird

I am trying to get my newly installed Cobra 75 Cb working. I tested it with an SWR meter and after trimming the antenna several times I am still getting a 3 reading. I tried running a ground wire from the mount to the vehicle, with no luck. I can hear the weather channels very well, but nothing on the CB. Any suggestions.

I have a 2008 Jeep JK with a 4' Firestik Antenns with a 50 ohm 18' Cable with the mount on the rear brake light extender.

RedneckJeep

Trimming the antenna does absolutely nothing except fool the SWR meter into "seeing" a better reading. It does NOTHING for the actual SWR at ALL. Have you checked the coax and shield with an ohmmeter? Disconnect it from the antenna and the CB. Measure the resistance between the coax (center electrode) and the shield (outer electrode). There should be NONE. In other words, it should read like an open circiut. Then, if that is ok, reconnect it back at the antenna and check the shield against ground. It should have continuity. The ground wire really should be connected to the antenna shield and NOT the mount. Grounding the mount is not onlt not necessary, but it also gives you more of a chance to lose ground down the road over time due to rust and debris since the ground has also been saddled with being the ground for the antenna as well. Grounding directly to the antenna shield cuts out the middleman so to speak. Make sure too, that you ground to the TUB and NOT the tailgate. Since the tailgate is held on with hinges and moveable, it is not a good ground source.

AK4Dave

What? I don't know if I'm understaning you correctly, but if so, and by you saying "it does nothing" then that's like saying you can use any length antenna for any band. So sorry guy, but I have to disagree with you there.
Trimming OR lengthening an antenna for a particular frequency does not "Fool" a SWR meter......it will either create better, or worse SWR for the SWR meter to see. Trimming or lengthening, ie tuning an antenna to resonate on a particular frequency (low SWR) allows the most RF power from the radio out through the antenna on that frequency, rather than an untuned antenna (high SWR) that reflects power back. So I don't understand how that's doing nothing?
Now put a tuner inline in the system and it will do what you say. A tuner will create an impedance match on an untuned antenna system and will fool the radio into seeing good SWR enabling the radio to transmit without harming the radio. It does nothing to tune the antenna, but does provide a match between radio and antenna feedline.
If this gentlemen saw that he needed to trim his antenna to resonance, and now he is not seeing any change in SWRs after a few "trims", then perhaps he's now trimmed it too short, or actually didn't need to trim, but lengthen it in the first place. To find out, he can clamp another short piece of wire to the stinger, maybe just alittle longer than the amount he cut off, key up, and see if that changes to a flatter match, ie lower swr. If it does, then indeed he went the wrong way and should not have cut the stinger, but lengthened, ie extended the stinger up from the mount. If there is still no change in SWRs then he might indeed have a grounding or coax problem. Is it possible that you may have a bad radio??? I mean, have you ran it before or is it brand new? If possible, hook your radio up to a friends antenna that has no problem and see if your radio works ok then. BTW...bad coax connectors can, and do create all kinds of problems.
Good Luck...

RedneckJeep

Read this and pay particular attention to number 8. Coax, antenna...it's all the same to the CB.

http://www.shadowstorm.com/cb/CB_Myths_Exploded.html

muddpuppy01

8) Trimming the length of my coax will lower my SWR.


think you need to re-read it that has nothing to do with the tuning " trimming " a antenna

coax has nothing to due with the antenna itself with it you can make it short or long as you please but the antenna has to be specific tune

getting a 3 swr sounds like either a bad ground, cable, or antenna placement or combination between them

Geko45

Trimming your coax (as mentioned in your link) does nothing to true SWR. Trimming your antenna does everything. Antenna length is the single most crucial element to obtaining a low SWR for a given band (i.e. CB).

AK4Dave

Red......merkerbird stated that he trimmed the "antenna" not the coax. Your #8 in the article also says "the coax". You must have missread it and thought he meant the coax. I guess that's why I couldn't understand what you were saying.
Senior moment?...... That's ok.....it don't make ya bad. I'm having more and more every day....