Question about Cobra 29 LTD CB Radio
D-23 is your reverse polarity diode.Change it and you'll be ok its a 1n4404
Posted on Oct 28, 2013
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Posted on Jan 02, 2017
When you say calibrate your radio, usually it means you are trying to re align the channels. However I do not believe that is the question you are trying to ask.
I think you are trying to ask is, "How to I tune my antenna?"
You cannot actually tune the radio. What you are probably talking about is your SWR. If so, Here is how to do it.
First make sure you are in an open parking lot. Structures like building, trees and other cars near by can give you a false reading.
Next with the radio on, turn to channel 20.
Make sure all the doors and windows are shut.
Flip the switch that is all the way to the left to CAL.
Key the mic and hold it. Then turn the knob all the way to the right marked SWR CAL up until the needle on the meter is all the way to the right at the little red triangle marked CAL. While still holding the mic key, flip the switch to SWR. The needle should swing back and will give you the SWR reading for that channel.
** try not to make any noise because if its picked up by the mic it will give you a false reading. Try turning the dynamic all the way down so it will not pick up sound."**
now if its 1.5 or lower your in good shape. You could always do better. If its 2 or higher your antenna is not matched. Here is how to tune it.
Use the same steps above to take a reading on channel 1 and 40.
You need to recalibrate each time you take a reading.
Now if the reading on channel 40 is higher then on 1 the antenna is too long. You need to make the antenna shorter. your antenna should have instructions on how to do this.
If it is higher on 1 then 40 its to short, it needs to be longer.
Follow the antenna instructions on how to adjust length.
Now if you really did mean, how do you align your radio, meaning tuning the channels, then you need an oscilloscope and a couple of other meters like a DMM and watt meter etc, and some specialized tools. Its also an involved process. I would suggest taking the radio to a radio shop. You can usually find them at truck stops.
Posted on Jun 17, 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
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