Question about Cobra 29 LTD CB Radio
Posted by Anonymous on
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Posted on Jan 02, 2017
SOURCE: squelch doesnt work
Open the component / speaker side cover on the radio, adjust VR3, this is the alignment control for the squelch. Set your squelch control knob on the front of the radio to about 10 o'clock and slowly adjust VR3 until the signal from the speaker is mute.
When you turn the squelch back to the 0 position, you should have signal with no squelch as in normal operation.
Posted on May 10, 2008
Wow. That's not at all a solution to what this guy is asking. And why all the caps??
The one point jm77437 has that is correct is that you do not set the radio, you set the antenna. The rest is blah blah.
Here is how you tune your antenna for you radio. First off it depends on what kind of antenna you have. most fiberglass antennas have a tunable tip to adjust the height of the antenna. Metal whips either have a collar at the base that the whip will either slide up or down in to adjust the height. The other type of metal whip's you have to physically clip to shorten the antenna, you must be careful with this type because once its clipped, that's it. You cannot add what you cut off.
I am going to give this example using a metal whip with an adjustable collar.
First after your radio is hooked up in the vehicle, drive to an open lot. Buildings and other structures can cause extra reflection. turn to channel 1. Flip the meter to CAL. Key the mic without talking. Now turn the CAL knob up until the needle reaches the little upside down triangle all the way to the right marked CAL. Now you have just celebrated your radio for your setup to measure you SWR. Now while still holding the key, flip the meter switch to SWR. The needle will move, and where it stops is your SWR reading. The lower the better. Anything under 1.5 is considered really good. But still, the lower the better.
Make note of what your SWR was on ch 1.
Now flip to channel 40. Repeat the SWR process. You must recalabrate each time you take a reading.
Now like jm77437 said. If your SWR reading is higher on 40 then 1, then your antenna is too long, and you must make it shorter. Loosen the collar and lower the antenna in the collar 1/4 inch at a time. check the swr each time you adjust the antenna.
If your SWR reading is higher on channel 1, then your antenna is too short. You must make your antenna longer. Do this by loossening the collar and pulling the antenna upward in the collar 1/4 inch at a time, again checking the swr each time you adjust the antenna.
What you want to achieve is having the same SWR reading on channel 1 and 40. then you have the best match you are going to get with that antenna.
If your swr is under 1.5 on all channels, you don't need to fuss unless you are a perfectionist. then by all means go ahead.
If your reading is higher then 3, or your ant light comes on, something is really wrong. Make sure your antenna is connected all the way, and the coax is not damaged.
Its important to have an appropriate SWR because if you do not, you are reflecting too much signal back into the radio, and eventually you will burn out your final transistor, and your radio will be toast.
Some tips: make sure you check the swr with the doors and windows shut. Make sure you are in an open lot. Remember to calabrate ecah time you take a reading. If you have had your radio peaked by a radio shop, and they have lowered your dead key, or have done a swing modification, then the meter in your radio will not work when taking an SWR reading and you will have to use an external meter.
Posted on Apr 24, 2009
You should not calibrate the antenna before you install it on the car!! the antenna needs to be calibrated on the vehicle that it is going to be on. Type of vehicle, different mounts, and many other variables can change the amount of reflection you will get.
j0hn9999 did a much better job but left some info out.
Take your SWR readings on channel 1, then on channel 40.... NOW, if your SWR is higher on ch 40 then ch 1, then your antenna is too long and it needs to be shortened. Refer to the antenna instructions on how to shorten the antenna.
If your SWR is higher on ch 1 then on ch 40 then your antenna is too short. You must lengthen the antenna. Again refer to your antenna instructions on how to lengthen your antenna.
You must calibrate each time you take a reading.
Make sure your doors and windows are shut when taking a reading
Make sure you are in an open lot when taking a reading as buildings, trees and other structures can cause reflection and give you an inaccurate reading.
If you adjust the length of your antenna on another vehicle and then put it on yours, the SWR will be off. It will need to be tuned again.
An external meter is better then the one in the radio, but will need to be hooked up in the vehicle you have the antenna on.
If you are not running any kind of power, or do not have a swing kit installed, and the radio is stock, the meter in the radio is more then enough to get a correct SWR reading.
Posted on Apr 24, 2009
Let's see you wanted more modulation, so you twisted the VR4 pot so hard that it broke off . First, if the radio has been clipped, VR4 is not in use . FYI, I think that full Counter Clockwise is wide open . VR4 is a 680 ohm pot, but can read to 800 ohm . Most folks defeat the AMC circuit by removing D11, C73 will do the same . You may actually be better off by leaving the circuit intact, and changing C71 from a 220uf 10v to a 33uf - 47uf at 16v, or 25v, to 50v . This will make the AMC transistor react faster for cleaner operation . Set VR4 so that it just prevents severe over-modulation . If you want modulation that bad, change C42 to a 3300uf 16v - 25v . That will increase available power for your audio amp . Make sure that R48 is 220K Ohm . For swing, remove Jumper JP36, and install a 18 ohm to 100 ohm 1 watt resistor(higher number = lower dead key) in parallel with a 47uf to 100uf 50v cap . I use axial caps, if you can find them, and piggyback the resistor . Outherwise, it can be mounted on the botton of the board . Make certain that the negative lead of the cap is in the rear hole . Without an amp, I use 18 ohm, and 47uf at 50v . I also add a "short" jumper on the bottom of the board from the audio transformer base ground to the center grounded area of the board to prevent feed back . You just have to jump a few small traces . The center area is grounded, follow skinny the traces . The jumper just beefs up the ground . Well, I hope that satisfies your lust for modulation ! J
Posted on Nov 28, 2009
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