CB radio help

[RayH]

I just installed a CB in my vehicle. I had a CB in it till last year I had to remove it to put a brake controller in. I also have CBs in other vehicles so Im not brand new to installing them.
Its a basic system, Ive only got $80 or so in it so I dont expect alot. Its just a little Cobra 19 hooked to a bottom loaded steel whip. The radio receives great for what it is. I can clearly pick up signals from mobile radios 5+miles away through the mountains.
Heres the problem. It isnt transmitting past line of site. I checked SWR and made adjustments. My SWR is excellent at less than 1.5 across the freq band. The built in meter is showing full power when transmitting. I did get a radio check from someone on a nice base unit that was about a mile away. He said he showed that I had good power but he could barely make out what I was saying like it was garbled and fuzzy. He suggested that my mic was bad. This is a brand new Cobra, right out of the box. I had another guy tell me I need to increase my modulation.?????? How do I do that without having someone jack up the radio for me? I dont want or need to put alot of money in this but I should be doing better than line of site. Any ideas? I dont have another mic I can try with this radio.

 

[bill177]

From what you describe, it will turn out to be a mic problem and nothing else. All carrier and no modulation or weak audio is just another way of saying the mic or mic amp circuit aren't doing what they are supposed to. Unlikely it is an adjustment, as most of the current batch of CB have very little that is adjustable inside of them.

Try a different mic. It must be from the same make and maybe model or the wiring may be different.

 

[RayH]

I guess I can visit work tomorrow or Monday. They use all Cobras in the trucks. Different models but I think the mics are the same. I'll call Cobra Monday also and see what they say and if I can get them to just replace the mic so I dont have to remove the radio and rewire it.

 

[JoeR]

Do you have access to a watt meter? Does your SWR meter show forward power? You should show 3 watts or so forward power. Although, your problem does sound like the microphone. Does the garbled audio happen when the vehicle is not running? Maybe alternator whine getting into audio circuit, or possible bad ground.

Joe

 

[RayH]

Do you have access to a watt meter? Does your SWR meter show forward power? You should show 3 watts or so forward power. Although, your problem does sound like the microphone. Does the garbled audio happen when the vehicle is not running? Maybe alternator whine getting into audio circuit, or possible bad ground.

Joe

My SWR meter does have a watt meter but I need a special fitting or something for it to work, I forget what it is, Ive never used it for that.
It happens with engine and all vehicle power off, as well as with engine running.
I know the radio has good ground because it has power. I did double check the ant ground and its fine. Wouldnt a bad ant ground show up as a high SWR?

 

[George2615]

Check your voltage (across red and black leads) when the mike is keyed and unkeyed. It should not drop below 11.5 volts with the engine off. Does the radio lights dim down when you key it up? If so you may not have a good ground. The vehicle should be running for optimum voltage supply to the radio. The radio will light up without the black lead even hooked up if the antenna is connected. Unhook the antenna from the radio in receive and see if it stays on. The radio needs a good circuit board ground which is the black lead out of the radio. The antenna ground is through the vehicle chassis. Did you wire it into your fuse box or directly to the battery? Your watt meter should have a switch or two to read forward and reflected power and shouldn't need a special fitting. Are you sure your checking the SWR properly. Another problem may be RF from the antenna getting into the mic.
My guess is going to be a poor ground but a defective new radio isn't out of the question.

 

[RayH]

Check your voltage (across red and black leads) when the mike is keyed and unkeyed. It should not drop below 11.5 volts with the engine off. Does the radio lights dim down when you key it up? If so you may not have a good ground. The vehicle should be running for optimum voltage supply to the radio. The radio will light up without the black lead even hooked up if the antenna is connected. Unhook the antenna from the radio in receive and see if it stays on. The radio needs a good circuit board ground which is the black lead out of the radio. The antenna ground is through the vehicle chassis. Did you wire it into your fuse box or directly to the battery? Your watt meter should have a switch or two to read forward and reflected power and shouldn't need a special fitting. Are you sure your checking the SWR properly. Another problem may be RF from the antenna getting into the mic.
My guess is going to be a poor ground but a defective new radio isn't out of the question.

Ok, that gives me some things to check. Actually the radio does dim ever so slightly when the mic is keyed so you may be onto something. I did check the ant ground and its good. Im positive I checked the SWR correctly, Ive done that a few times before on other radios and I double checked on this one because I am having issues with it. I have it wired through the fuse box. I had a CB installed perviously and removed it this summer, This new one is wired in where the old one was, I just used crimped connectors to splice the new radio in. My last radio was a cheap RadioShack brand and the antenna sucked so it had high SWR but still got out much better than this new one.
How and what would cause the RF from the ant to feed back to the mic? Wouldnt that only happen if the SWR is off? My SWR is actually very good, below 1.5 on all freq. My antenna is mounted on the rear drivers side corner of the hood, so it is in close proximity to the mic and radio with only about 3' of air and a windshield between. (I know, the hood isnt the best place but I carry a canoe and kayaks on the roof, loading and unloading them really limits roof mounting, at least I get some ground plane from the hood). I could probably do alot better with a center or top loaded ant. I should still get out further than line of site with the setup I have.
I'll go back and check the ground and volts tomorrow. I'll also refresh myself on the SWR meter instructions to see what I need to check watts.

 

[RayH]

Check your voltage (across red and black leads) when the mike is keyed and unkeyed. It should not drop below 11.5 volts with the engine off. Does the radio lights dim down when you key it up? If so you may not have a good ground. The vehicle should be running for optimum voltage supply to the radio. The radio will light up without the black lead even hooked up if the antenna is connected. Unhook the antenna from the radio in receive and see if it stays on. The radio needs a good circuit board ground which is the black lead out of the radio. The antenna ground is through the vehicle chassis. Did you wire it into your fuse box or directly to the battery? Your watt meter should have a switch or two to read forward and reflected power and shouldn't need a special fitting. Are you sure your checking the SWR properly. Another problem may be RF from the antenna getting into the mic.
My guess is going to be a poor ground but a defective new radio isn't out of the question.

Ok, I did some more checking today. Heres what Ive got.
Volts across red and black with engine off = 12, volts with engine running = 13.5-14, Heres something I didnt expect, Volts across red and black with mic keyed = 18 ??? Any idea how that can be?
I did check power output (I need an oscilator if I check SSB, thats what I was thinking I needed but I dont) Power output is 4 Watts when Jeep is running and just a hair under that when not running. I disconnected the ant and still have good power to radio, With the Ohm meter I checked all grounds from ant and radio to vehicle chassis and they are good.
The only thing I see thats odd ,(besides 18 V when keyed), is that the radio dims just a little when keyed. I guess that could indicate that Ive got a weak connection, weak ground or need heavier power wire but Ive still got good transmit power (4 W). It should be getting out.

 

[RayH]

Im suspicious of the low SWR I was getting. The needle would barely move on channel 40, and would only go up to about 1.25 on channels 19 and 2. I did some reading and those numbers are not normal, they are too low, for a mobile CB system. I read that an antenna can be so badly matched or adjusted that it will absorb the signal and not transmit it and not feed it back to the radio, showing extremely low SWR but still not transmitting anything.
I switched antennas out for an old 2' fiberglass I used when off roading. My SWR went up to 2 on channel 19 and between 2.5 and 3 on channel 40 and channel 2.
I just had a very clear and strong conversation with someone about 1 miles away through the hills.

 

[George2615]

RF is the signal that is radiated off your antenna when you key the mic. As you see with your meter it reads 18V when you key up. This is an example of RF power being radiated into the 12V power leads to the radio and RF into your voltmeter. 3 ft. between the antenna and mic is kinda close. I had a similar problem with a Ham rig in my truck. When I keyed up I had so much RF getting into the power leads and mic that the radio VFO would change frequency. I had to do three things to correct my problem.

First was to use a top loaded antenna instead of base loaded. (I use the std. 3/8 - 24 thread antenna mount so they are easy to change). This change radiates the majority of signal off the top rather than bottom of the antenna.

Second I had to coil up and tape the excess coax to act as an RF choke which stops th RF from following the coax back into the radio. You also should have at least 19 - 21 ft of coax between your antenna and radio or some multiple of 1/4 wave length for the frquencies you use. Don't make the coax as short as possible.

Third I did the same to the power leads coiled them up and taped. I also bought some choke suppressors at Radio Shack that clamp over the coils of coax and power wire to reduce RF getting into the radio.

Just read your last post and see you have a 2' antenna. If you can do it get a 4 or 5' top load antenna with a tunable tip like the truckers use and you'll see a big difference in signal both received and what you send out.