CB radio help

[RayH]

So is the 18 V a problem? There shouldnt be any RF radiated back to the power source right? Can I use that as a gauge of how much RF Im loosing back to the radio?
Ive got 18' coax. Ive always heard not to coil the coax?
I think youre right about the RF and the antenna being too close to the radio. Ive got the antenna mounted on the hood and the radio is mounted between the visors so the radio is actually higher than the antenna.
I did a little more just to see what happens, The antenna I was using was a bottom loaded antenna. First I took that off and put the little short fiberglass antenna on. It worked much, much better than the bottom loaded steel whip. Then I removed the coil off the bottom of the whip (I had a basic ant mount from another vehicle to use) and it works marginally better than the fiberglass antenna. It seems the coil at the bottom was the problem. I think probably the best antenna for this setup would be a tall top loaded ant or at least a center loaded ant.

 

[RayH]

I just checked the volts with mic keyed and the new non loaded whip. I now have 20+ volts between the red and black. Im confused now because this antenna works better than the other but apparently is feeding more RF back into the power wire. Does the 20v represent how much RF Im pumping out of the antenna or how much im loosing back to the radio?

 

[George2615]

No it doesn't. The 18 or 20V you see is a false reading. Unless you have a semi truck running a 24V system your car alternator should show 14 - 14.5V when running. RF is radiated energy sent through the air. It can be measured with a field strength meter but readings vary based on how the signal is reflected off the vehicle. I still think you need an RF choke as I described before and yes a top loaded antenna will work better for local talking while a base loaded will work better for skip or DX talking due to its higher angle of radiation. The 18-20V reading you see from RF is affecting the voltage the radio gets from your battery. That is not good for the radio since it's designed to work from 10.5 - 15V. If you ever had the cover off the radio you'd see that most parts (especially capacitors) are rated for 16V max. RF energy getting inside a radio through the coax or the power leads can cause oscillator voltages and parts values to change creating audio distortion or frequency deviation.

 

[bill177]

Hey RayH - did you ever get it working? I'd sure like to know what the problem was.

 

[RayH]

Hey RayH - did you ever get it working? I'd sure like to know what the problem was.

Nothing new to report. I got busy and put it on the back burner for a couple days. I did go buy a longer whip thinking that if I could get the signal above the roofline it would be better. I didnt see a noticable change. I think my problem is the location of the antenna in relation to the radio. Not sure what Im going to do about it though.

 

[Paul2000]

It sounds like a bad mic. You should only have a few basic elements to check on the radio. Receive and Transmit. You say you receive the guy with the base fine at a distance so the receive side sounds good.

The audio quality of the transmit portion can be tested by getting someone with a radio closer to you verifying it is clean, or tune a scanner to the frequency if you don’t have a spare CB to have someone listen on. Here are the frequencies the channels actually transmit on. CB & FRS Radios FAQ

If they are parked a short distance from you and it is garbled then RF power out is not a factor. You said you measured the power out and the SWR. It sounds fine. 4 watts out is the max legal limit on a CB and the lower the swr the better. There is no such thing as too low SWR. I use to tune them until I could not see the SWR needle move at all when I keyed it. The reason it changed when you changed channels is it is a direct indicator that the antenna is matched to your frequency. If the antenna is tuned to channel 20 and you move to 40 you have moved away from the frequency it was tuned to. An antenna will support a deviation from it’s center frequency and work fine, but on a CB it will only be tuned for one frequency.

If the audio sounds poor at a close distance then you probably have a bad mic. At that point you need to try a different one on your radio, or try yours on a different radio to see if it makes the other radio sound bad. Good luck. Paul