Question about Cobra 29 LTD CB Radio

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How do I calibrate my cb to match my antenna - Cobra 29 LTD CB Radio

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1. You calibrate the antenna to match the CB rather than the other way around. Some antennas can be adjusted while others cannot. This should not cause a problem since the ones that cannot be adjusted generally don't need adjusting. The ones that can be allow for fine tuning to get a better match.

2.To match your antenna to your CB you set the SWR (Standing Wave Ratio) to it's lowest possible setting. SWR is the ratio of power that gets out through your antenna versus the reflected power that gets sent back to the CB. You want to get the most power to go out, or forward, through the antenna as this drives the signal that others receive. To set your SWR;

3.Connect an SWR meter between the antenna and the CB using a short piece of Co-ax cable. Set the switch on the meter to Forward Power. Key the CB and adjust the dial on the SWR meter until the needle of the meter is fully forward. Release the transmit button and change the switch on the swr meter to Reflected Power. Key the mic again and note how high the needle goes. If the needle doesn't go into the red it's safe to use but the lower the reading the better.

4. To bring it down check your antenna. Some antennas have a telescopic tip that can be extended or reduced by loosening a nut near the top. Try extending it fully and repeat the procedure at paragraph 3 above. If your SWR rises then try reducing the antenna length and check again. It's a matter of finding where you get the lowest swr by making smaller adjustments from the best of the 3 settings above.

5. You'll probably find that when you get a low SWR on one channel it will be higher on other channels. This is because of the frequency difference. Unless you use one channel nearly all the time, it's best to set the swr on the middle channel so if you have a 40 channel CB set the SWR on channel 20. The further you change up or down the higher the SWR will increase but it should be still within the safe range. If you set the SWR on say channel 1 the SWR will be twice as high when you change to channel 40 than it would have been if you set it on channel 20.

6. Most people never check their SWR so if you're using a commercial CB antenna, rather than a home made one, it should be factory set to give a reasonable match so if yours cannot be adjusted it's probably matching ok. A more common problem to look out for is the connection from the antenna to the CB. Make sure that the screening wire and the centre core are not touching. Even a single strand of the screening touching the centre wire will cause screeching on your transmission and before long will cause your CB to stop working. 73s and enjoy your CB.

Posted on Apr 03, 2011

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1 Answer

Cobra 29 refuses to calibrate


Check for a short in the Coax. Is the antenna near the cab of a truck or other body part? Is the antenna grounded? Has your radio been peeked and tuned?

Mar 09, 2013 | Cobra 29 WX NW ST 40-Channels Base CB...

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When I key up on my cobra 29 Ltd my swr goes up to the red.. Is that normal and if not where should it be and how do I correct it to where it should be


Its hard to tell, but it looks like your meter switch is in the Calibrate position.
Also while keying in this position I noticed you meter had not reached the correct calibrate point on the meter.
First you switch your meters control switch (the 2 switch) to CAL, then using your SWR calibration knob you move the meter until it matches with the CAL knotch on the meter itself.
After it is as perfectly lined up as you can get it, move the meters control switch to SWR mode, then key down again.
This should give you the accurate reading of your radio's SWR's.
If they are still to high then your having 1 of 3 issues.
(1). Your antenna is not tuned
(2). Your antenna's mounting bracket is not making a good ground with the vehicle.
(3). You my have a coax issue or a bad connection between the radio 7 the antenna itself.
Now if you have anymore questions I recommend you visit my facebook page, a cb club made for beginners to the cb radio hobby.
I can answer all questions you might have, even walk you through how to tune your antenna.
Search for Citizen's Band Central, if you believe your radio setup needs a professional look, find my radio business on facebook.
Search for Radio Communications & Installations.
I hope this has helped you, & good luck.

Feb 05, 2013 | Radio Communications

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I cannot get my swr meter to calibrate to check swr. My radio has been tuned and peaked. I have 18ft of coax, and I have run extra grounds to the antenna and the radio. Why can't I get it to calibrate?


where do you have it mounted?Is the antenna an adjustable one with set screws? You may have to move the antenna up and down to get a good match. Anything under a 2.0 is good.

Oct 08, 2012 | Cobra 29 WX NW ST 40-Channels Base CB...

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How to match a antenna to a cobra 29 LTD Classic


You are actually tuning the antenna to the vehicle it is mounted on here are some very good resources. http://www.rightchannelradios.com/pages/cb-antenna-tuning-guide-pv-c0-61.htmlhttp://www.wilsonantenna.com/swr.php

Be aware that if your radio has been modified it may produce a dirt signal that an swr meter may read as reflected power. In this case it may be more accurate set with a unmodified radio also if your radio is setup for a linear it may have a deadkey to low for the swr meter to calibrate correctly.
Hope this was of help.

Nov 26, 2011 | Cobra 29 LTD CB Radio

1 Answer

Which pots do I use to calibrate swr and rf meters on 29classic to match extral meter?


VR5 tx power meter VR6 antenna warning light
There is not pot for swr cal internally. I guess the cal knob broad range pot or variable resistor. Swr readings after user calibration knob on front of radio, for meter should be close. Obviously not as good as external with larger scale meter. If you can not calibrate meter on face with this knob your radio may have less than 4 watts deadkey.
Just to be on the same page. Understand that SWR is a reading of antenna system condition or tuning of antenna to vehicle mounting location. This is a brief description.

Jul 07, 2011 | Cobra 29 LTD CB Radio

1 Answer

I have full power but no white noise as they call it.it wont calibrate either.when useing swr or calibrate switch.


Turn your RF gain all the way up. There is no need to turn it down. Make sure the squelch is down. Also, some days it's just really quiet out. You can turn the radio on some day and hear nothing. Or you could have a problem with the mic.

As for the calibrating. You do not calibrate the radio. that is for calibrating the meter to read the SWR of the antenna. Here is how to tune our antenna.....

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 12, 2010 | Cobra 29 LTD CB Radio

1 Answer

29 LTD CB Radio: Calibrate cb radio...


The CAL is to calibrate meter for reading SWR (standing wave ratio) which is reflected power when transmitting back to receiver(radio) from antenna system.
This CAL switch position when selected and mic keyed uses the CAL knob to align the meter needle with inverted red triangle next to cal on meter. Then when you select SWR switch position meter will display accurately when mic is keyed for that channel. Now notice the difference when you go between channels 1 and 40. The ant led light will act as idiot light if it is not lit then you are most likely safe to transmit.
I say system because your vehicle, antenna and coaxial cable are all part of this system. When you have a high reading and have to trim you antenna this is really calibrating the antenna to the vehicles body which acts as a ground plane.

May 16, 2010 | Cobra 29 LTD CB Radio

1 Answer

Cobra 29 NW LTD Classic wont calibrate and red antenna light keeps coming on


The calibrate knob only calibrates the radios SWR meter, the owners manual will show you the procedure for that. If your ANT light is coming on, it is telling you that your SWR is to high, and may cause damage to the radio from reflected power. You should purchase an in line meter as the radios internal meter may be somewhat unreliable. You need to tune the antenna to the lowest SWR possible. Typically anything under 2.0:1 is acceptable. Radio Shack sells a meter for about $50, and is pretty accurate. Antenna mounting can also cause high reflection if it is to close to other objects. Google "CB antenna tuning" or read the instruction manual for you antenna, and you should be able to figure out how to properly tune the antenna.

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Uniden pc78ltw


The pc78 is the same chassis as the cobra 29 so any info you san find on the cobra 29 will work the same for your pc78..What kind of problem are you having?? Chia

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Matching Antenna, or ??????


If the antenna is tunable, you definitely need to start out by having the swr set properly on the antenna. Also, make sure the plastic ferrel, (the small round white piece) is between the top of the antenna bracked and the antenna itself. It is there to make sure the antenna does not ground out to the vehicle. If the antenna is grounding out, it will be like no antenna at all. I have also had a few customers that have had broken coaxes straight out of the factory package on cheaper antenna setups.

Dean
Rollin CBs

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