Question about Cobra 29 LTD CB Radio

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Terrible static We are having a big problem with interferance when driving by low lying electrical wires and/or other semis. SWR's are fine. We have tried moving the antenna's. Still the problem exists. Any ideas?

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  • truckerswife Sep 19, 2007

    The antennas are fiberglass. The radio is connected directly to the battery. When I plug in my GPS or my phone charger into the power source (cigarette lighter) the noise comes back through the radio. I have to turn the squelch up on the CB to get the noise down.



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There should be a switch on the radio labeled ANL/NB make sure that the switch is in the on position for both of these. those are the automatic noise limiter and the noise blanker always leave them in the on position, this should stop your problem.

Posted on Sep 17, 2007

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What type of antennae are you using? If you are using an aluminum or stainless steel ant, I would suggest switching ti a fiberglass ant. It sounds like the metal ant is picking up the ambient voltage from the lines. If you are using a fiberglass already let me know, as you may have a more serious problem. Good Luck and I hope this helpsd L8R

Posted on Sep 17, 2007

  • Anonymous Sep 22, 2007

    Sounds like you need a noise filter on there.
    I have a 10" sub in my truck and needed to put one in for my CB as I was having the same problem, the noise filter I used got rid of most of the interfernce.

    Check this link, it gives you several other possibility's you can try.

    And you can purchase filters from this link

    Good Luck



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My 2011 tahoe has terrible static. It is only the radio, I have no problems with clarity if I use a cd, ipod, phone or my xm satellite stations. It is the stock radio that cane in the truck.

Get an inline suppressor which will cut down the static interference from the trucks ht leads and wiring.i believe it fits onto the negative lead of the radio assuming your truck is negatives earth.available at small cost from most auto shops.

Feb 27, 2015 | Audio Players & Recorders

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High static level

Hi Gary,

It sounds like something may have loosened up. Given that this is installed in a truck it is probably subject to quite a bit of vibration. This could have broken a connection, etc. If this just started, consider what happened just before you noticed the change. Maybe the truck was serviced just before - consult with the mechanic to learn what he or she may have done to contribute to the problem. Maybe the antenna smacked a low hanging tree limb?

You could disconnect the antenna from the radio, and spin a metal protective cover over it to prevent signals from entering. If the static sounds are reduced, the interference is probably coming from the antenna system. If it remains, it is probably coming in on the power leads. With the ignition OFF, check for noise. If reduced or eliminated, it is related to the engine / electric fuel pump (if equipped), etc.

Check the PL-259 connector at the end of the coax cable. If the braid or center connection has failed, it should be repaired be removing the connector and preparing the cable to receive a new connector again.

Make sure the ground wires and braids are firmly connected at the radio connector end and at the antenna. Rust is a poor conductor and if present will interfere with transmit and receive. Clean it up, make your connections up tightly and then seal to prevent water from entering.

Check antennas for damage. Many antennas on trucks are fiberglass because they're tough. The wire wrapped around it however is soft copper. If the antenna has smacked tree limbs, overpasses, etc. they could have been damaged. The physical shock is transmitted down to the mount point - causing it to loosen up, etc. Repair and replace suspected damaged or loose parts. Make sure the rubberized weatherproof tip on Firestik type antennas are secure and in place.

Check the coax. Make sure the outer jacket is continuous and has not been compromised by being crushed between pinch points, chafed, etc. The jacket must not have splits or cracks that would allow water or oil in. Replace any damaged coax cable with identical type and lengths - this is especially important in a co-phased antenna arrangement as I understand is your current configuration.

A high SWR can also cause problems. Most manuals say 2.0:1 (two point zero to one)is maximum acceptable SWR or "match". I could go along with that provided that value is present of infrequently used channels - like 1 and 40. The channels used most often should have a very low SWR. 1.1:1 (one point one to one) to as much as 1.5:1 (one point five to one) is where I would expect to be on channel 20 (the mid point of the band). There will only be one place that the is the low point in the band. Transmitting further up or down the band from 20 will cause the SWR to increase. Eventually, you will exceed 2.0:1 and too much power will be reflected back into the radio - potentially causing a failure of the RF output final transistors. This is only increased if running a linear amplifier. Transmitting at a lower power make dealing with a higher SWR much easier than sending high power to a mismatched antenna system. Your set up may have a nice, wideband of acceptable match - 1.5:1 on ch1 and ch40 with 1.1:1 on ch20; or be very narrow banded like 3.0 (or more) :1 on ch1 and ch40 and 1.5:1 on ch20. It could even be "way out there" with 4.0:1 on ch1 and ch40 and 2.5:1 on ch20. if you've got a bad match happening, correct it ASAP!

Check you power source. The best place to grab power is directly from the battery. Yours may be there already, and even so, it may also have noise reduction components such as a choke input filter and or capacitor on the power leads. Look for these and other components inline and inspect for damage or contamination by oil, fuel, etc. Replace as needed. Check the power leads for any connected accessory, too.

That's about all I can think of.. good luck!

Jan 29, 2012 | Cobra Radio Communications

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

We are trying a radio check for a mirage 66 but the static only goes away when we turn the squelch all the way down and we can't hear anyone

Sounds like you have a lot of interference. Could be something in the vehicle causing all the noise. Try it with the engine off. Also make sure the antenna system is correct. for example, coax good. antenna grounded. SWR low. etc.

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