Question about Uniden PRO520XL (40 Channels) 2-Way Radio

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Antenna type,length,etc i would like to get more power from my cb so if there is any hints or tips for a higher power output i would love it. the main thing iam after is what type of antenna, what length, and diameter,also isit true the higher the better. thanx for any feedback

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Buy a wilson 1000 or 5000 magnet mount mount it on your roof

Posted on Nov 11, 2009

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Yes it is true that higher is better. First try a "Silver Rod" you may clamp it on to a long Scaffold pole to get it even higher but be sure to tie guy lines to it in case it falls or take it down in high winds. If you need a mobile solution look for "twigs"(aerials) that have at least one "coil" on them, you can get ones with more these are better. Lastly the longest you can find, higher up, and least coaxial cable that you can will all help. If it is legal where you are you could install a "Burner" though these are illegal in the U.K.

Posted on Dec 26, 2008

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How do you tune cb radio 75wx st

Not sure what you mean by tune.

If you mean peak and tune, where in you increase the internal power output of the radio, then the quick and dirty way of doing it is, turn VR4 all the way to the left and take the tank slug out of L14. HOWEVER, I prefer to use a watt meter on avg power to adjust L14 to peak, and no more as not to over bias the final. But typically nothing will happen if you do. This will give you full modulation, and full carrier.

If by tune you mean, Tuning the SWR. Then that is a whole different topic.

In this case you don't actually tune the radio. You tune the antenna. If the antenna is not the correct length, relative to the wave length, Frequency of transmission..... then you will have a high SWR and this means more of your RF energy is not leaving the antenna, and going back into the radio. This is bad. this kills radios.

So to tune it you must make the antenna the right length. Here is how to check SWR.

Tune the radio to ch 20. Put the rf/SWR/CAL switch to CAL.
Turn the CAL knob all the way to the left.
Key the radio, and turn the CAL knob to the right until the needle of the meter is at the CAL mark, on the top line of the meter indicated by a little upside down triangle. That is the cal mark. The needle should be on it.
Flip the RF/SWR/CAL switch to SWR while holding the key down.

The meter is now showing your SWR. If it is under 2 you are not real good, but not gonna kill the radio. If you are 1.5 or less you are good to go. Ideally you want to be 1.5 or less if you can.

If it is over 2 you should try to get it lower.

here is how to find out if the antenna is too long or too short.

Turn to ch 1, repeat the steps to check SWR. Then do the same thing on ch 40. Compare the reading. If the reading is higher on 1 then on 40 the antenna is too short, and you need to make it longer. If it is higher on 40 then 1, it is too long and you need to make it shorter.

All antennas have a way of adjusting the length.

Hope this helps.

Aug 10, 2012 | Radio Communications


SWR Setting

Antennas for all radios need to have the SWR set, STANDING WAVE RATIO. Which means the antenna needs to be the correct length for it to work properly. Most people stick them on and start talking.. This is not good pratice to do. The lower the frequency the longer the antenna needs to be. The higher the frequency the shorter it needs to be. ie. 80m ham antenna needs to be around 67 ft long. and a wifi antenna needs to be just less than an inch. soo, Your CB is on 26.965ch1-27.405ch40 so ch1 is lower freq than ch 40.
obtain swr meter. inline with the radio - meter - antenna..
check swr first on ch1. then check 40 if there both good try to even out both so that there around 2.0 or less ideal is 1.1 to 1 or 1.5 to 1....
Now if ch1 is higher than ch40 = need to raise the antenna make it longer.
If ch40 is higher than ch1 = need to shorten the antenna.
some antennas have an adjustable whip. ie wilson, k40, predator10k, etc.
just adjust the whip to obtain low swr ...
some other antennas don't have whips to adjust. like Francis and OEM antennas on most trucks from the factory. these either need cutting like francis. or the oem style has a cap and wire wound under it. trim little bit at a time.1/8inch or less. if you never set swr before always try to find a good HAM operator to help you. or a decent cb shop. MOST will not charge you to do them. and Good Amateur radio operators and Good CB Shops will have an Antenna Analyzer made by MFJ.. This is what we Use here at our shop.There more accurate then a analog meter alone. And it will not interfere will people on the air like a swr meter.
Anyone that needs help please feel free to contact us. We're glad to help.

on Dec 11, 2009 | Radio Communications

1 Answer

I just purchased a cobra 29 LTD Classic mobile CB radio.Pro tuned high performance Mosfet Final I have a palomar 450 LD mosfet linear.will i have any problems?

Not if the power output from radio to amp is set correct and the jumper for coax is correct length and there is absolute perfect match between them and the antenna used. Afterthought: also the amp better be connected to something big enough to power it.

Apr 29, 2012 | Cobra 29 LTD CB Radio

1 Answer

How do I calibrate my cb to match my antenna

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.

Apr 03, 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...

1 Answer

Can hear people but they cant hear me

It could be either of the following.

A bad mic.
poor antenna or not properly tuned antenna.
blown output transistor due to improperly tuned antenna.

If you have never tuned the antenna, and have no clue what the SWR reading is for the antenna, its a good bet that the radio may be shot.

when the antenna is not tuned to the proper length, it will cause some of the RF energy to bounce back down the feed line, and into the radio, and damage the final output transistor.

Sep 25, 2010 | Cobra 29 LTD CB Radio

1 Answer

My swr rating is really, towards 3 on everychannel. tried to ground the anntennas and it didnt work. thanks.

3.0 is way too high for the SWR reading. Check your coax and length. I always preferred 3-foot increments, such as 12, 15 , 18 feet, etc. 18' is good because that's a half-wavelength for the middle of the Citizen's Band frequencies. Check grounding at the antenna mount. Also, I have run across "floating grounds" between the truck body and frame...not too often though. That will cause a high standing wave ratio. If you're using a fibreglass antenna, make certain wire has not been cut, or broken from the tip of the rod. If so, that can make an antenna/radio very difficult to tune properly. Try another antenna on the mount if necessary. I hope you find this problem, because it's not good for the transmitter to be subjected to a high amount of reflected RF power coming back to the radio, for very long. Good luck.

Aug 03, 2010 | Cobra 29 LTD CB Radio

2 Answers

Whats the best height for a base antenna

best height is as high as possible.
height = might

Dec 13, 2009 | Raytheon VHF 53 CB Radio

2 Answers

How do you tune and peak a cobra 29 ltd classic and how many watts will it put out after it is tunned and peaked

i would highly suggest you take it to a cb shop to get a cb tuned and peaked. before you do that though, make sure you have a good antenna system. a good antenna will have a much greater effect on your cb than tuning and peaking. as far as output, who knows? it all depends on the skill of the person doing the tuning. be warned that any output over 4 watts is illegal and you could recieve hefty fines if caught with an illegal radio.

Sep 23, 2009 | Cobra 29 LTD CB Radio

1 Answer

When I key the mic the radio blinks out and then comes back on

This can be due to one of several problems. Insufficient sized wires to the power source or a high SWR (standing wave ratio) between transmitter and antenna. The first is probably not a problem unless connected to an RF amplifier to boost output wattage. A high SWR however, is a more likely culprit. SWR is a ratio of power out of the transmitter to power that is reflected back from the antenna. Ideal theoretical ratio or "match" is 1:1. Real life is more like 1.1:1 (one point one to one). Most transmitters are perfectly happy with a match (or mismatch as the case may be) of 1.5:1 or even 2:1. Beyond this is asking for trouble. A mismatched antenna system can cause the failure of the output final transistors.

Matching or lowering the SWR of a radio to an antenna system requires that an SWR meter be installed between the antenna coax or cable and the transmitter's antenna connection point. There are two types of meters - dual needle and single needle. The dual type is more expensive, but easier to work. The meter must be capable of working on the frequency it is to used on. This means if it is marked as a 400 - 512 Mhz or UHF type, it will not be accurate on 27 Mhz or HF.

Once the meter has been installed, transmit at half power (or at least the amount needed by the meter) on the highest frequency and take readings. Do the same at the lowest and a middle frequency and record findings. Physically adjust the length of the antenna whip - by no more than 1/4" inch (for 27MHz CB frequencies) and check again. After a few tries, you should begin to see how shortening or lengthening the whip changes the SWR of the system. Once set correctly, the middle frequency will have the lowest SWR value while the lowest and highest frequencies will have equal higher SWR values. It would go something like this: Ch1 = 1.6:1 Ch 20 = 1.2:1 Ch40= 1.6:1 Of course, if Ch1 = 1.7:1 and Ch 40 = 1.6:1 that would be fine, too.

Double check everything once more at full power, so that you know the transmitter won't be damaged under full power conditions. Make any last adjustments and lock everything in place.

Aug 21, 2009 | Radio Communications

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