Unit is mounted in my big truck.
Pulled it out one day and heard a rattle. Opened the bottom and found one of those tuning screws floating around. (looks like a set screw, goes in one of the threaded tubes with the copper wire windings around it.) There are two hollow tubes without screws that I can see. A black one at the back left, and a brown one at the back center next to where the antenna hooks up through the back panel.
Seams like people can hear me for a good distance, but I lose them at 1/4 mile or less.
Also, the two empty tubes and the screw have no sign of the thread locking wax like stuff they used on the center screw .
I have worked on a few of these. And I believe the slug needs to be put back in the one next to the antenna,or you can look a the white lettering on the board next to it and it should say L11. It, will be right under your antenna connector. You, will need to have a tech do this so it can be set correctly. It takes a meter to get adjustment just, perfect, however. If, you would like to chance it, you, could put it back in and use a peace of rubber band between the slug and the housing to hold it in. I would try it with about 1/4 of the slug still showing out the top. But you really need a cb guy to check it, and your SWR.
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Re: loose tuning screw?
What you are looking at is a powdered iron core from one of the tuning coils in your unit. They are used to match circuits together. The brown tube is the one it is out of. The screw is used to match the output of the amplifier to the antenna. All systems are a little different so you need a way to fine tune the system. The closer the circuit is to matching, the more power it will transfer. The fact that the one tube is black and one is brown (and near the antenna output) leads me to conclude that it goes in the brown one. There definitely needs to be one on the antenna output to match it. The black one is probably plastic while the brown one is cardboard or fiber. If that is the case the black one never had a tuning coil because it is a fixed value inductor. How do you know how far to screw it in? If you have an SWR meter (or a friend you can borrow one from) hook it up, do a calibration, put it in the "reflected mode", and while transmitting turn the screw in until the meter drops to it's lowest and begins to rise, then back it out 1/2 a turn. You should see the meter begin at a high level and drop as you turn in the screw. This is because as you get the system impedance closer to a match there is less reflected wave and more signal propagated from the antenna. This should result in improved reception for you and your friends. It would also be a good idea to put a drop of household glue on the screw threads to lock it in place. Don't overdo it though because you may need to retune it in the future if you get a new antenna or change anything in the system. Good luck.
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I took a "Pringles chip" rounded container and wound 8.25 ft of fine copper wire around it from top to bottom with a screw up top(bore into cardboard) holding it in place, and a***Shiny" screw **attached to the metal bottom. Then i took 8.25 ft. and placed it inside of the Pringles can. I punched a hole into the plastic lid and pulled through the wire to go to ANTENNA INPUT. Sitting it on top of the radio I let the metal bottom touch the GROUND by a screw. I keyed the radio it matched the same as my Antenna did. It keyed the exact same 1.5 watts and swinging to 4 watts when I whistled on my PC68Xl Uniden 40 ch. CB radio. Make sure both ends are stripped of enamel coating by scraping it off. I use a cigarette lighter for this or my teeth, or rough sandpaper, or nail polisher. The screw up top of canister is not important --it just holds the wire,so to easy wound the wire. I gapped it about 1 inch apart between windings.
Odds are it is your antenna or coax more likely coax or a ground issue with them.
Make sure your antenna in mounted correctly a pinched coax can have a dramatic affect on reception.
Beyond that Cobra has a hit and miss record on quality control but there is no magical blue screw. There are 9 tuning coils that if tuned incorrectly will degrade or make your reception intolerable. A receive alignment for a reputable shop would improve the reception even though this is most likely not the problem.
It is possible that you have had quote "the front end" damaged referring to a pair of diodes but that usually happens when your radio is close to someone running a lot of power. Truckstops are good for that.
The best way is with an antenna analyzer but that is too expensive unless you do SWRs for a living. The meter on the radio should suffice for your needs.
Adjust the screw on the antenna until it is about 1/2 inch out.
Place the srf/swr switch to swr.
Go to channel 1 and note the SWR reading on the meter.
Go to channel 40 and do the same.
If channel 1 SWR is higher than channel 40, then screw the tuning screw out a turn or 2.
If channel 40 SWR is higher than channel 1, then screw the tuning screw in a turn or 2.
Repeat until the SWR on channel 1 is the same as 40. Channel 19 will be the lowest.
If you are not comfortable using the built in SWR meter, you will have to invest around $20 for a small SWR meter.
You need to take off cover locate wires to that switch and cut them loose from CB/WB and buy a Toggle switch to mount outside radio and switch it on/off like to make CB/WB selection..Seems that switch inside is screwed. needs new one. I would rigg it myself. By drilling hole in cover and placing outside toggle with white marker saying Cb top Wb bottom.
Several things are working against you.
1 Antenna location= Needs to be in CENTER of car or truck, and high. no grounded metal can be next to the element (the hot/positve part of the antenna)
2 the only way to really ground the antenna is by having a flat metal ground plane under the antenna. DC grounding does NOT do this, that is a misunderstanding.
3 make sure you use a tunable antenna. I have found the wilson's to be very easy to tune and performe very well, for a base loaded antenna.
4 in short a wilson or k40 magnet mount placed on the very top of the roof in the center will have a perfect ground plane. Then shorten or lengthen the steel whip to ajust your SWR's. You will get the best results this way. This is the ONLY way to achevie good performace.
5 I will say this the absoulte best antenna is the 102"steel whip, if you got the clearnce and dont mind it hitting tree limbs put it on a big magnet mount with a spring at the base and youll have a perfect antenna. But the wilson is shorter and easier to tune.
Turn it to channel 20, flip the switch to CAL, key it up and tune it by the SWR knob to the set position, which it a small red triangle. With the mic still keyed, flip the switch to SWR and see where it reads. If its over like 2 on the meter its your antenna tuning. You can complete the rest of the test by doing the same on 1 and 40. But if your that far off you can do the calibrate test all day long and never get it right. Ask one of the other drivers to take a look in between loads or something like that. Its more than likely either improper antenna tuning or a ground plane issue. Not a big deal just frustrating.
Pitcrew, does the noise go away when you screw the pl259 down tight? Find someone talking on a channel and do the PL test again and see if their signal disappears when you screw down the PL. Have you done an SWR test yet? Is this a fairly new antenna? If this problem came into my store, the first thing I'd do would be an swr test, the second would be to test with a volt/ohmeter from the center pin on the PL to the metal stinger to make sure there is a connection.Then check from the trunk mt to the outer ring of the PL for connection. Now, if you check from the center pin to the outer ring of the PL you should not have connection! If you do, the coax has a short in it,,, Is this mounted on a trunk of a car? Sorry for all the questions, but there are so many different things it could be, and I'm just trying to narrow it down for you. Hope this helps some, let me know,,, Mechanic
I assume your coax is not hooked up properly or you have some kink of a short in your antenna connection ( thats if your cb is working properly ) Radio Shacks Information that suggested that the 102" whip is the perfect antenna is their opion only as I prefer to recommend a full wave antenna system to my customers, but I do assure you, the 102" whip does work well if it's properly installed. I have found the main problem in the 102" whip installation is when the center hole is cut to install the antenna, it's not cut big enough, which grounds the antenna. It's not suppose to be grounded in any fashion to the automible chassis. The ground of this antenna comes from the 3 screws mounted around the outside of the antenna mount. Check that for sure. If you can't correct the problem. write me back at this web sight of direct at email@example.com. Good Luck