Question about Cobra 29 WX NW ST 40-Channels Base CB Radio

4 Answers

Loose tuning screw?

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 . Thanks

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4 Answers

Normaly they have a thin rubberband run down inside the tube to hold the tuning slug inplace.

Posted on Aug 25, 2007


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.

Posted on Jan 01, 2007

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And don't forget to do the tuning on the center frequency Ch 20. is close enough.

Posted on Jul 20, 2006

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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.

Posted on Jul 20, 2006

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