Question about Cobra 29 LX

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SWR displays briefly then back 1.1

Have been trying aerials for fiberglass motorhome. Is need for ngp the problem?

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Your problem is not very well described, but let me guess: while you transmit, SWR peaks shortly to a high value and then drops back sharply.
There are two possible reasons:
1) Strong radio transmission pulse somewhere very close to the antenna;
2) Bad contact between connector and coaxial cable somewhere between SWR meter and antenna. Points to check:
- Coaxial connector on the cable from SWR. Is it soldered properly?
- The coaxial cable: can you see mechanical damage, stress? If you find scratches, broken isolation, sharp bends, etc, try to replace the cable.
- Connection between coaxial cable and antenna (or connector): is it soldered properly, is it not corroded or mechanically damaged?
- Connections inside the antenna (if there are any such joints): look for corrosion and mechanical damage, also loose screws.

If you find multiple places of potential problem, go step by step from antenna towards the SWR meter: if the most distant problematic location is fixed and it still shows this strange behavior, go closer.

Rarely this could be a problem in the SWR meter itself. That can be identified if you replace antenna by a dummy load. Dummy load should never cause bad SWR "flashes" (unless it is mechanically broken, too).

Posted on Apr 01, 2014

  • David Thompson
    David Thompson Apr 01, 2014

    The SWR meter is built in to radio. Dumby load do tests without aerial?

  • OK4RM Apr 01, 2014

    If it's built-in then everything I wrote remains valid, you are looking for problems between transceiver antenna connector and antenna. Dummy load is nothing but a resistor having the same resistance as is the transceiver's coaxial output characteristic impedance (usually 50 ohm, sometimes 75 ohms) and sufficient power rating. It can be bought or, sometimes, home-made (for lower frequencies, let's say not more than 30 MHz if it is carefully built).


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I agree with OK4RM but he forgot to mention that the problem could be the fiberglass motor home , no ground plane , also how high does it peak to.As long as it doesn't swing to over 3.0 it won't hurt the radio.Its not great either.

Posted on Jun 28, 2015


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Newbie here. U was trying to tune my trc 447 swr but am having more than 3 to 1 regardless. I have checked the antenna system and its fine. Can anybody help me. Thanks

What kind of antenna do you have ? If it a fiberglass whip you may or may not have a tuning rod that may be in the tip of the antenna. If you have a metal antenna then you should be able to adjust it . First,get an external SWR meter and attach it to your radio with a 12" section of jumper coax from the radio to the transmitter side of the meter then your antenna coax goes to the other connector. Now loosen the tuning rod using the alan wrench and set screws on the antenna. Next , place the whip or rod to the bottom and bring it 1/4 " then key you radio and check your swr on channel 1/40/and 19. Write down the numbers you get and then readjust and recheck it. Always writing down the results until you are at least a 1.5:1.

Jan 23, 2016 | Radio Communications

1 Answer

I have a cobra 25 ltd classic with firestik ngp antenna , using swr meter I cannot get a match.

Make sure you have a good ground on the antenna and radio.
Check the SWR at Ch 1, Channel 20 and channel 40.
Does the SWR reflected power improve as you go up in channels or get worse.
If it gets better, the antenna is too short, if it gets worse the antenna is too long.
Also when you say a match, are you trying to get 1.1 to 1?
This may not always be possible depending on the antenna. Anything 1.5 to 1 or lower would be acceptable.
And again check your grounding, most Radio and RF issues are a result of poor grounding and poor antenna positioning and poor groundplane for the antenna.

Good luck

Oct 16, 2014 | Radio Communications

1 Answer

How to set standing wave

The SWR is set by the antenna. It depends on the type of antenna you have as to the correct procedure. If the antenna has a stainless steel whip then a set screw is loosened so that the whip can be adjusted up and down. Most Fiberglass antennas have to be trimmed. Some of the fiberglass antennas have tuning adjustments under the rubber cap on the end. Check you SWR on channel 1 and on channel 40. If it is higher on 40 than it is on channel 1 then your antenna is too long and needs to be shortened. If your SWR is higher on 1 and lower on 40 then the antenna is too short. There are many articles on the web concerning SWR. I urge you to read up because having the SWR set on your rig will ensure many years of good operation and performance.

Mar 10, 2013 | Cobra Radio Communications

1 Answer

The light for high swr keeps coming on. replaced antenna and coaxle. how do i go about lowering the swr. is there a nob or switch for this. thank you

You cannot lower the SWR via the radio. it has to do with the antenna. The length of the antenna is essential to transmitting properly. It must match the transmitting frequency.

To check SWR tune to ch 20. Flip the meter switch to CAL. Key the radio without talking into the radio. Turn the CAL knob up until the meter needle is at the CAL mark. Unkey the mic. Flip the meter switch to SWR. key the radio again, and the meter will show your SWR. We already know it is high because you are getting antenna warning, but we will have a base line now to work on.

What you did was calibrate the meter for that channel. that is necessary to check the SWR. So you must calibrate for each channel you check.

You should at least be under 2 swr. Ideal is 1.5 or under. the lower the better.

If your SWR is high, your antenna is either too long or too short. To find out here is what you do:

Check the SWR on ch 1 and ch 40 calibrating for each channel. Compare the difference of the SWR between 1 and 40. If the SWR is higher on 40 then 1, your antenna is too long. If your SWR is higher on 1 then 40 your antenna is too short. All CB antennas have a way to adjust the length.

If its a mag mount, its usually a set screw you loosen to raise or lower the whip. Fiberglass antenna's usually have something under the cap at the tip to adjust. It will either be like the mag mount, with a set screw and a small rod to raise or lower it, or a screw, that you screw in or out to make it longer or shorter.

make small adjustments. 1/8th or a 1/4 of an inch at a time. Each time you make a change, take an SWR reading on 1 and 40 again and compare the difference. The difference should be getting less. Do this until there is very little or no difference between 1 and 40.

Then you go back to 20, because it is the center channel and check the SWR there. It should now be low. If you did a good job it will be under 1.5 and you are good to go.

Aug 07, 2011 | Galaxy Radios DX-93T Base CB Radio

1 Answer

I hooked everything up the way it said but i get nothing on every channel....also when i drive i here a lot of feed-back

Im not sure feed back is the correct description. You can only have feedback when you transmit. I think you are talking about interference from the car.

First lets address the issue of hearing nothing....

  • Make sure the coax is tightly screwed onto the back of the radio.
  • Depending on the type of antenna, for fiberglass antenna, make sure its grounded properly, for mag mount, make sure there is nothing wrong with the mebrane on the bottom of the magnet, and that you haven't put anything in between the magnet and the car.
  • Make sure the mic is plugged in. You will have no receive if there is an issue with the mic.
  • Make sure you have tuned your antenna. This is important. If you don't you will ruin your radio.
As for the interference. Some times devices in a car can cause interference to the radio. Here are some ways to battle that.

  • Make sure ANL is turned on. This is the Automatic Noise Limiter.
  • If you have the power wire connect into the fuse box, try running it straight off the battery.
  • If that does not stop the interference, then got to a truck stop, and get a power wire noise filter.
Also, I am including information on tuning your antenna below.

It is important to tune your CB radio antenna to the proper length. The length must exactly match the wavelength of the frequency you transmit on. Or be really really close.

All Cb antenna's have a way to adjust the length of the antenna. If it's a mag mount, the metal whip can be slid in and out of a metal collar. Usually a set screw. If its a fiberglass whip, the way to tune it is on top. It either has a small metal rod with a set screw to adjust the length, or it threads in and out to adjust length.

Either type you have it will need to be adjusted for proper length. Here is how to tune the antenna to lowest SWR.

Some radios have a built in SWR meter. Some do not. If yours doesn't have an SWR meter, then you have to use an external SWR meter. Radio shack carries one, and you can find them cheap on ebay.

If you have a built in SWR meter or external, the procedure is the same:

1. Turn the radio to CH 20.(This is the center of the band.)
2. Switch the meter switch to CAL. (CAL stand for calibrate.
3. Key the radio. (Important. Do not talk while keying the radio.)
4. turn the CAL knob up until the meter hits the CAL mark.
5. Now while still keying the radio flip the meter switch to SWR.

Where the meter falls after that point is you SWR reading. If its above 3, that is real bad. 2 is not gonna kill your radio but its not the greatest. 1.5 and under is a good place to be, but the lower the better.

If your SWR is high, Here is how to find out if your antenna is too long or too short.

1. Turn to CH 1
2. Repeat SWR procedure. You must calibrate every time you do it.
3. Remember the SWR reading.
4. Turn to CH 40.
5. Again repeat SWR procedure.
6. Compare the reading between CH 1 and CH 40.

Now if the SWR is higher on channel 1 then channel 40 your antenna is too short. You must make it longer.

If the SWR is longer on channel 40 then on channel 1, then the antenna is too long, you need to make it shorter.

Make height adjustments about an eight inch at a time, and take reading each time.

once the SWR is significantly lower and the reading on channel 1 and 40 are about the same, you a about matched. At this point turn the radio to the center of the band, channel 20 and take an SWR reading.

You should now have a low SWR reading, 1.5 or under. If you are 1.5 or under, you are good to go.

If you cannot get the SWR to an appropriate level, there may be an antenna problem.

Nov 15, 2010 | Radio Communications

1 Answer

Having trouble setting swr .moved anttena up and down 1/4 inch at a time and there is no change

There are several things that can cause you not to be able to get an acceptable SWR.

The first is the most obvious. Poor antenna, or bad coax. Make sure your coax is good. Make sure the antenna is mounted in a good location.

Some things I have seen that cause this problem.

  • Wilson Little wil, almost impossible to get under a 1.6 SWR.
  • Fiberglass antenna's, a break in the wire near the top of the antenna. Will show the antenna as being too short, and adjusting the top will do nothing. This antenna is no good.
  • Common mode current. This is when the RF is traveling back down the outside of the coax, and or causes the coax to act like part of the antenna. SOLUTION. As close to the antenna as you can, take 6 to 8 inches of coax, and coil it into a tight coil, about the diameter of a spray paint can. In fact using a spray can to wrap the coax around works well. Use electrical tape to secure the coil so that it will stay tight and uniform. This will stop common mode.
  • missing foil/vinyl membrane on bottom of magmount antenna. This is essential for the antenna to see ground plane.
  • bad connections on coax connector.
  • Cracked isolator on stud mount.
  • incorrect procedure for taking SWR reading.
  • Poor location of antenna. E.g. antenna's load not above roof of vehicle.
  • Incorrect length whip being used.
  • corrosion of any part of the antenna system.
There are some cheap antenna's out there that you just can't get lower then say a 1.5 or worse, like the wilson little wil. Wilson makes great antenna's. The 500, 1000 and 5000, as well as their silver load antenna's are excellent. I have been able to get them all to at least a 1.1 SWR, and some like the 5000, and silver load fiberglass whip to 1.0 using an analyzer. The Little will is just a poor antenna. Anything under 2.0 SWR is okay of a barefoot radio, although I don't like going over 1.5 my self. A barefoot radio, will do a 2 swr all day. If the radio is stock, and not peaked and tuned, 2 swr is fine and won't hurt the radio.

You should always try to get the lowest SWR that you can in any case. The lower the SWR, the more RF energy is leaving the antenna. As well, receive will improve the closer you get to a perfect match. This is known as being "On Que".

Check everything I have listed that applies. And if nothing fixes it, you may want to try a different antenna. Some antenna's just don't work well on certain vehicles.

Oct 13, 2010 | Cobra 29 WX NW ST 40-Channels Base CB...

1 Answer

I have a cobra 29 ltd bluetoot. with builtin swr meter that reads 2.0 on channels,40,1 ,20 when testing is this low enough .what can i doo to get it lower

what type of aerial are you using? is the aerial near any metalwork ie fencing/metal sheeting etc if so move it away as you could be getting reflected power back into the aerial causing high swr, also 2.0 swr isnt too bad could be better but the swr meters built into cbs are not that acurate, I would use a dedicated in line swr meter (even a loan of one) and compare the readings, I take it all your electrical conections to the aerial are good? let me know and i will try and help, Thanks.

Jul 14, 2009 | Cobra 29 LTD CB Radio

2 Answers

My swr is too high, was 1:1 WHEN I INSTALLED 2 WEEKS AGO

Something has changed in your system. Check all of your connections and grounds. Thats where I would start.

Jul 05, 2009 | Superstar SS-3900EGHPA CB Radio

2 Answers

Uniden pc 78 elite cb

Hi, This is a link to your old post re SWR 3.... As stated SWR 3 is too high, it should be 1.5 or lower. Fiberglass antenna are kinda notorious in setup and experience wise have not performed well or at all. Maybe you should try a different antenna (metal rod). Some good brands/models I have tried with very good results are K40, Hokushin, Comet, Oscar, Maldol, Daiwa. To check if you can receive, stick an ordinay length of wire ('bout 9' long) at the center of your radio's connector. RX should work (pls don't key the mic or TX).

Aug 12, 2007 | Uniden PC78ELITE 40-Channels Base CB Radio

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