Question about Cobra 25 LTD 40-Channels Base CB Radio

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Breaking up When transmitting the sound on the other end goes faint and breaks off compleatly. We have a full wave antenna with top quality coax cable mounted on the side of a metal building. we switched out the radio but still had the same problem.

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Hello richf, With out a complete rundown of what you have, I'm sort of guessing here, but I'd say offhand that you are not using a base antenna. Most "full waves" are usually mobile fiberglass antennas. If this the case, Get the antenna above the metal siding, you might be getting a "reflection" back from the metal skin and causing a extreme high SWR which will cause damage to your radio, from a short period of talking. Either go higher up to clear the siding or put up a mast pipe and order or buy an Antron 1/2 wave base antenna. Those are a 3 piece fiberglass base ant. that is tunable for different situations. Run roughly about $50.00 but solves so many problems,,,Let me know more info and I'll try to help the best I can,,, Mechanic

Posted on Nov 01, 2008

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How do I adjust my swr on cOnex 3300

SWR is adjusted at the antenna. I am not sure how familiar you are with SWR so forgive me if I repeat something you already know.
The first thing you need is a way to measure SWR, an SWR meter. Theses can be found on ebay or elsewhere. The SWR meter attaches to the radio with a short coax cable of about 2 feet or less. The other connector on the SWR meter goes to the antenna coax. Once hooked up you should see a switch that reads forward and reverse or abbreviations of such. Place it in forward position. Now there should be a knob adjustment that you can turn. You key the radio, meaning press the mic button to transmit. While holding the button and transmitting adjust the knob on the SWR meter until it reads exactly full scale. After you have done that flip the switch to reverse while transmitting and read the value shown. At the low end it should read 1,2,3,4 etc. If you are lucky it should be between 1 and 2. If so say it is 1.5 then you can say your SWR is 1.5:1 which is ok. If you had a 2.0:1 Swr you would be losing only 11% of your power, giving you 89% still going out the antenna. 3.0:1 would be a 25% loss and so on. Really not that big of a deal. But some radios need better than that or they will reduce their power slightly or not at all if its too far off meaning something is terribly wrong with the coax or antenna. If its less than 2.0:1 I would just leave it alone. But if you find in reverse that the meter goes way over to the right, then you need to find the problem. a shorted or open coax or same with antenna. If you are ok with swr but just want to play and dial it in better than all you do is raise and lower the antenna ever so slightly by loosing the set screw at the base of the antenna. Make sure you mark the old spot in case you need to return it back to that position. Now on other antennas there will be an adjustment at the very top of the antenna that can be turned. Like a carbon ferrite type of screw inside the antenna. This is of course for a short antenna. If you are using a 1/4 wave whip which is the best to use in my opinion kit is around 102 inches long. gives you more range and better receive. If you drive a truck then that is out of the question. But somthing that is overlooked is the fact when you take the meter out after you are done checking the SWR. Your SWR will change and wont be what you just had with the meter in line. So leave meter inline or do this: Most meters have a field strength option. What you do is attach a small wire antenna to the SWR box where there is a small screw hole for it to attach. If you dont have an antenna make one out of a bout a 10 inch stiff copper wire. In this test you will not be hooked up to the cb radio with your SWR meter. Hook you cb back up just to the antenna coax to your antenna. Key the mic again to transmit, tape it into place to hold it there. Now put the swr meter on forward or field strength if if has a selection for that. Now walk away from your antenna about 10 feet so with the adjustment turned up all the way for full meter deflection on the swr meter you should see it get stronger as you get closer to the antenna or weaker as you move away from it. You are actually seeing the power coming from the antenna. You can now set you meter on something away from your antenna where you can see the meter but dont have to hold it. Note the reading. Go back to the cb and stop it from transmitting. You can now make adjustments to your antenna then transmit again and look at the meter. Did it go up or down? Ideally you want maximum meter deflection for maximum power. I f you hook up the swr meter again with cables and it shows something other than 1:1 doesn't matter because like I said once you take the meter out or put it in the swr changes. you are changing the length of the coax. What matters is maximum power right? That's what most people try to achieve by adjusting swr. But like I said on that too, really you wont be able to tell the difference on the receiving end of somebody elses CB when you are talking. To be real you would have to 4 times your power in order for the s meter to go up one s unit on your buddys receiver while you are transmitting. So don't get lost in in all the CB hype of other peoples theory of how important swr is. Your radio is looking for about 50 Ohms of value to work as it should. a 2.0:1 swr would say that it is seeing either 25 Ohms or 100 Ohms. The coax cable should be rated at 50 Ohms meaning if there is 50 Ohms t the other end the coax will be 50 Ohms if you were to measure it at any point on the line. But if there is anything different, then these rf waves travel from your radio to the antenna where if not 50 Ohms will not consume or output all the power at the antenna and the result is waves not going out will come back toward your radio, hence the reverse setting where you are seeing this happen. This can be so involved and yes just because there might be 50 Ohms at the antenna doesn't mean the antenna is resonating at the right frequency. This is why the field strength is important too. The value where the coax meets the antenna ideally should be 50 Ohms but it can be anything because of the design and length of the antenna. So you see you can be moving the antenna in and out to make it 50 Ohms but at the same time you are changing the frequency it wants to emit the best too which could be different. So to say the swr can be off a little if you get more power coming out of the antenna. Sorry for such length but hoping it makes more sense for you.

Jul 17, 2016 | Radio Communications

1 Answer

Receives but won't transmit

It's hard to say , there are lots of reasons.
Check the coax connection to the antenna at both ends. Or better yet the another antenna and coax, or try an on set whip antenna to verify the transmitter.
Hope this helps.

Mar 14, 2015 | Radio Communications

1 Answer

When i press the mike two red lights are coming on end the reception isn't good how do i fix this problem

Green changing to Red it normal operation from receive to transmit.

However the ant light should not light it is to indicate the SWR= standing wave ratio.This does not normally indicate any reduction in you ability to receive signal it only refers to reflected power from you antenna system to your receiver/cb. You may have a insulator in the wrong location. If it is an solid mirror or body mount the mount must be grounded with no insulator on coax side and an insulator on the antenna top of mount antenna must not be grounded.
If you have a coax that is damaged and i mean even bend from pasting thru a door or other "pinch point" it may be bad.

Sep 16, 2011 | Cobra 29 LTD CB Radio

1 Answer

Won't send out. I have replaced mike already.

if the Mic gain is up. and an antenna is connected. its possible that the transmit circuit is blown out. this is definitely the case if you have been operating the radio and the red ant lift has been lighting when you key up. that means your antenna was not tuned to the radio and your swr was too highroad. swr is standing wave ratio. basically if the antenna is not exactly the right length thenyou create a standing wave that does not leave the antenna and bounces back down the coax into the radio which destroys the transmit circuit. if when you key and there is no signal output then it is shot.

but make sure the cb pa switch is on cb.

Jun 15, 2011 | Cobra 29 LTD CB Radio

2 Answers

I drive a Freightliner Columbia and have 2 Wilson 2000 antennas. My SWR is at a 2 and sometimes higher, while the truck is running. If the truck is off, it goes below 2. Unlatch the door, it goes lower and...

hello dcigno when you say you have two wilson 2000 antennas you mean cofaced this could be down to the lengths of coax ,are both coax lengths the same if not you would not get a perfect match also check the pl259 connectors on each antenna make sure there is no short whatsoever iff all fails just use the one antenna , and see how that works for ya ,for a more technical term the antennas should be a 1/2 wave apart taking into account the lengths of coax ,hope this helps you out above all check coax for breaks or faults goodluck

Mar 30, 2011 | Cobra 29 WX NW ST 40-Channels Base CB...

2 Answers

29 cobra ltd c.b. wont transmit or receive. mic antenna coax are good

make sure the RF gain is all the way up, and the dynamic is all the way up or most of the way up.

When you say the antenna is good, have you checked the SWR's and or have tuned the antenna to be the correct length for the radio? If this has not been done ever, your radio could be a brick.

Also, make sure the PA/CB switch is on CB. if its on PA(public address) it will not receive or transmit because it is on PA mode, which if you have one hooked up, a PA speaker, then you can talk to people through it out side your car.

Also, make sure the S/RF SWR CAL switch, its the first one on the left, is all the way up on S/RF. this is your signal/ receive setting for the meter. When you hold the key, does this needle swing forward? As well does the RX/TX light turn red? If it does, then the radio is transmitting.

There is another light on the radio under the TX/RX light. It is the Antenna warning light. If this light comes on when you transmit, or has come on all the time during transmit, and now it doesn't then the radio is a brick. That is a warning light. It means that the antenna is not matched, or has not been tuned to the radio. If this has not been done ever, you have killed the radio.

Here is why. When you transmit, you are sending off a radio wave. This radio wave, at 27mhz, is about 36 feet long. In order for the wave to radiate off the antenna, the length of the antenna has to match the length of the radio wave. Now it does not have to be a full 36 feet. It can be an exact multiple of 36 feet. In other words it can be 1/4( one quarter) or 5/8(five eights) of a wave in length. 1/4 of a wave is 108 inches, or 9 feet long. Your antenna is still probably does not seem 9 feet long, but there is usually a loading coil that is not exposed making up the rest of the length of antenna, so that it matches the length of the radio waves electrically. If you were to stretch the coil out with the antenna whip, it would be 9 feet long.

When the antenna does not match the wave length, part of the RF energy does not leave the antenna, and goes back down the feed line(coax) and hits the transmit transistor. Prolonged reflection to the transmit transistor, otherwise known as the final will blow it out. As well depending on how bad the length was off, the more off, the more reflect energy, the more RF energy you are blasting back into the radio, and this causes more things then just the transmit to blow out. Some time the receive goes along with it when it finally goes.

So if the RF gain is up all the way, which by the way is basically how much receive you have, and there really is no reason to have it down at all, and the CB/PA switch is on CB and the needle does not swing forward when its on the S/RF setting, chances are that the radio is now no good.

It is fixable, but if there are no CB shops near you then you will have to send it out. And Cobra will not cover this under warranty because its stated in their warranty that they do not cover damage due to high SWR.

Apr 06, 2010 | Cobra 29 LTD CB Radio

2 Answers

Hello, I need help with a cb problem. My radio isn't reaching or receiving any thing farther than 100 feet. I just rewired it directly to the battery and I have a fire stick antennae.

Having that short a range would give me the indication that there is a disconnect in the antenna system. Here's a couple of clues: Is the connector on the back of the radio connected to the coaxial cable?

If it is not factory installed connector, is it possible that the solder job on that connector was bad? If the cable is old, it could have a crack in the coax.

Is it the RIGHT kind of coax? It should be an RG-8, and RG-58, or a variation of those types of cable. It would likely be marked with "50 Ohm" somewhere along it's length.

Is the connection at the antenna solid? A firestick antenna for CB looks like this:

You must make a good connection at the base of the antenna from the center coax conductor that does NOT short it to ground, and the ground conductor should attach to the antenna mount frame.

With your symptoms, it is very likely that either the center conductor has worked loose, has become unsoldered from the terminal lug, or your coax has come unsoldered from the center pin. All of these things would really honk up your SWR, or Standing Wave Ratio, which is sort of like a string on a guitar that is tuned to a specific frequency for a specific note. The center freq of the CB band is 27.155 Mhz, so you would typically "tune" your antenna for that to be the lowest. A firestick KW is not tunable, so that should not be an issue. Look to your coax at both ends, and the coax itself to find your problem. If you have a simple ohm meter it would help to locate the short circuit. Good luck, write back if you need some assistance in further troubleshooting.

Apr 02, 2010 | Radio Communications

1 Answer


its the coax. i had this same issue. i thought a bought a great strand but, it was very poor in design and it developed many breaks over time, reducing its transmitting ability. I would also check the mic wire and head connections as well. this is a problem spot at times.

Feb 25, 2009 | Cobra 25 LTD 40-Channels Base CB Radio

1 Answer

CB Squeal When Transmitting

I believe the coiled coax may indeed be the problem. To check, try a temporary rerouting of the cable which eliminates the coils. Dave g.

Dec 20, 2008 | Galaxy Radios DX-44V 40-Channels Base CB...

4 Answers

CB Squeal When Transmitting

Grounding the antenna bracket is extremely important, if it's bolted into the metal frame or fender it should be OK. The coiled coax cable could be the culprit but that's only a remote possibility.Try running a separate groung wire from the radio mounting bracket (or one of the radio's cover screws if not using a bracket) to the CLOSEST vehicle ground...keep this a short as possible. Your problem is definitely caused by insufficient ground at either end of the coax, with the antenna side being more suspect.

Mar 15, 2008 | Midland 1001Z 40-Channels Base CB Radio

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