[nos4you]

I recently installed a Cobra 18 WX ST II Mobile CB radio in my truck.
I used the 12v Power outlet as a Power source for my Radio.
Im running a 4ft Firestick and 18" coax(firestick also).
I calibrated the radio w/ the SWR meter with the engine off and all doors closed.
My reading was as low as 1.2(ch1) and as high as 1.6(ch 40)
I put everything back together and noticed that when im driving with the CB on that at least 3 bars(on the LED Receive lights) are always on sometimes it goes to 4.
When I use the CB with the engine Off I get no LED's untill I receive a signal or i Transmitt.
Is this normal? Did I tune it properly or am I missing another step?
Am I suppose to tune it with the engine on?

 

[Smiling_Jim]

I'm a HAM and a CBer...

And have had a General RadioTelephone license for 30 years, but I am going to guess here, at what's going on.

There's a lot of RF energy radiating off of a car ignition, and your receiver front end may be picking that up. Make sure the coax shield (ground) to the antenna has a good metallic ground to the car body. Have you gotten any 'radio checks' from other CBers to see if you are 'loud and clear' when transmitting? What do they sound like on receive?

 

[nos4you]

I have tested it with a friend of mine on the freeway for a lengthy time and we have no problem holding a conversation of up to 2 miles on the freeway. I can hear him loud and clear and he can hear me loud and clear.

My antenna is mounted on a bed bar and the bed bar is bolted to the bed(which should be grounded). I did scrape of the paint on the bed bar mounting hole before mounting my Firering Connector for the Coax on the Antenna side.

Will using power source directly from the battery instead of the 12v power outlet make it better?

 

[nos4you]

How did you guys tune u're antennas? with the engine on or off? and do u get any Receive bars lit up while on standby?

 

[ShowStop]

I recently installed a Cobra 18 WX ST II Mobile CB radio in my truck.
I used the 12v Power outlet as a Power source for my Radio.
Im running a 4ft Firestick and 18" coax(firestick also).
I calibrated the radio w/ the SWR meter with the engine off and all doors closed.
My reading was as low as 1.2(ch1) and as high as 1.6(ch 40)
I put everything back together and noticed that when im driving with the CB on that at least 3 bars(on the LED Receive lights) are always on sometimes it goes to 4.
When I use the CB with the engine Off I get no LED's untill I receive a signal or i Transmitt.
Is this normal? Did I tune it properly or am I missing another step?
Am I suppose to tune it with the engine on?

No need to tune the antenna with the engine on, that doesn't affect the tuning. What you are getting on the receive seems like engine noise. This is the problem with going through a power source being fed by the alternator, which is anything on the fusepanels. In these situations, you have to run the power leads straight to the battery to reduce the noise. Have you turned on the Soundtracker feature? That should keep the noise down.

Another possiblity is that the CB traffic in your area is pretty high and you are just getting lots of bleed from other transmitters. Skip conditions aggravate this and spring/fall are the big times of the year for skip. Just flip to Ch 6 and see what kind of noise you pick-up on there.

 

[nos4you]

No need to tune the antenna with the engine on, that doesn't affect the tuning. What you are getting on the receive seems like engine noise. This is the problem with going through a power source being fed by the alternator, which is anything on the fusepanels. In these situations, you have to run the power leads straight to the battery to reduce the noise. Have you turned on the Soundtracker feature? That should keep the noise down.

Another possiblity is that the CB traffic in your area is pretty high and you are just getting lots of bleed from other transmitters. Skip conditions aggravate this and spring/fall are the big times of the year for skip. Just flip to Ch 6 and see what kind of noise you pick-up on there.

I have tried the soundtracker feature, it helps a little but not enough. Most of the time I have to turn the squelch more than half way on which greatly reduces my range. It won't be a problem going directly to the battery. I will try that & let you know. Does any of these symptoms equate to a bad ground or anything else I can check? Oh by the way, whenever I lock/unlock my doors I get inteferance on the speaker.

Thanks for the response ShowStop! I knew you would know! Ill let you know how it goes.

 

[GOT COPE?]

I have mine running straight to the battery and still get a lot of noise. Ive been told this is from the fuel pump.
The electric fuel pumps cause a lot of RF noise/interference and in extreme cases the best solution is to put noise filters on the electrical wires running to and from the fuel pump.
However I have chosen not to do this as it sounds like a PITA, so for now Im dealing w/ all the noise.
One thing I can do when I only want to receive from close by, is to turn my RF knob down until the noise disappears. (I have a Uniden PC 78 LTW) your radio may not have this feature. But if I wish to receive best as possible (to hear far away and weak signals) I have to crank the RF up and deal with the noise.

 

[nos4you]

I have mine running straight to the battery and still get a lot of noise. Ive been told this is from the fuel pump.
The electric fuel pumps cause a lot of RF noise/interference and in extreme cases the best solution is to put noise filters on the electrical wires running to and from the fuel pump.
However I have chosen not to do this as it sounds like a PITA, so for now Im dealing w/ all the noise.
One thing I can do when I only want to receive from close by, is to turn my RF knob down until the noise disappears. (I have a Uniden PC 78 LTW) your radio may not have this feature. But if I wish to receive best as possible (to hear far away and weak signals) I have to crank the RF up and deal with the noise.

I ran power to my radio straight from the battery. It seems the same as when it was running off of the 12v power supply. I have to put my squelch in about the halfway mark to get it right after all the noise disappears. I guess this is as good as it gets. I do NOT know if having the radio directly under my CDplayer/stereo has anything to do with the interferance because I can here myself through my stereo speakers when i transmit with my stereo on.

What squelch level does everyone place it at right when the noise disappears?

You guys think putting a noise filter in the main power line would help any?

 

[ShowStop]

I have tried the soundtracker feature, it helps a little but not enough. Most of the time I have to turn the squelch more than half way on which greatly reduces my range. It won't be a problem going directly to the battery. I will try that & let you know. Does any of these symptoms equate to a bad ground or anything else I can check? Oh by the way, whenever I lock/unlock my doors I get inteferance on the speaker.

Thanks for the response ShowStop! I knew you would know! Ill let you know how it goes.

Try adding a separate ground lead to the radio chassis. Use one of the chassis screws to attach the ground lead. Does that help? Sometimes the electrical interference from nearby sources can be eliminated if you add that second ground. If if doesn't change anything, leave it off.

The door lock noise sounds like your coax might be running near some power leads. Did you run your coax down the driver side of the cab or passenger side? I'd recommend running it either up the middle next to the transmission hump or down the passenger side by the door, there are less power wires in those areas.

 

[nos4you]

Try adding a separate ground lead to the radio chassis. Use one of the chassis screws to attach the ground lead. Does that help? Sometimes the electrical interference from nearby sources can be eliminated if you add that second ground. If if doesn't change anything, leave it off.

The door lock noise sounds like your coax might be running near some power leads. Did you run your coax down the driver side of the cab or passenger side? I'd recommend running it either up the middle next to the transmission hump or down the passenger side by the door, there are less power wires in those areas.

I did run the coax on the passenger side then across the carpet/foot area of the passenger side. I have a 4door so I didnt want to bother running down the middle.

I will try the second ground next time I take apart the center console. I will just use it as it is for now.

 

[Gargoyle]

A couple of things to check:
- what type of coax are you using? It sounds like you know what you are doing, but I have heard of folks using 75 ohm by accident (or ignorance).
- when you say you calibrated your radio, did you trim your coax to different lengths or just use a tuning feature in the radio or the SWR meter?
- I would suggest dismounting your antenna from the bed bar, and making a temporary mount that sits above your cab (grounded maybe to a screw at the hi-vis break light). You note you have a 4’ firestick, which would say that you have about half of it below the top of your cab. This can cause a couple of problems: one is that your ground plane is now below the antenna (good) and at a mid point of your antenna (bad) which will change it’s radiation pattern from an omni directional to non-specific lobe pattern and may greatly reduce your transmission range and your effective tuning at different frequencies not to mention directions. You would be amazed at the difference a 9’ (1/4 wave) antenna and a tuned connection (proper length coax) will do for the radiated power of your system. I run one on my ’86 Toy mounted on the roll bar (dead-nuts center of the truck) and with an old Cobra people always think I am running a linear amp (“foot warmer”) to boost it’s power.
- did you leave the SWR meter in the circuit? Just checking on this one.
- for the noise, you are going to have that problem. Modern vehicles are very noisy. Try a low-pass filter on the power supply to the radio. Good ol’ Radio Shack should still carry those.

 

[nos4you]

A couple of things to check:
- what type of coax are you using? It sounds like you know what you are doing, but I have heard of folks using 75 ohm by accident (or ignorance).
- when you say you calibrated your radio, did you trim your coax to different lengths or just use a tuning feature in the radio or the SWR meter?
- I would suggest dismounting your antenna from the bed bar, and making a temporary mount that sits above your cab (grounded maybe to a screw at the hi-vis break light). You note you have a 4’ firestick, which would say that you have about half of it below the top of your cab. This can cause a couple of problems: one is that your ground plane is now below the antenna (good) and at a mid point of your antenna (bad) which will change it’s radiation pattern from an omni directional to non-specific lobe pattern and may greatly reduce your transmission range and your effective tuning at different frequencies not to mention directions. You would be amazed at the difference a 9’ (1/4 wave) antenna and a tuned connection (proper length coax) will do for the radiated power of your system. I run one on my ’86 Toy mounted on the roll bar (dead-nuts center of the truck) and with an old Cobra people always think I am running a linear amp (“foot warmer”) to boost it’s power.
- did you leave the SWR meter in the circuit? Just checking on this one.
- for the noise, you are going to have that problem. Modern vehicles are very noisy. Try a low-pass filter on the power supply to the radio. Good ol’ Radio Shack should still carry those.

As for the Coax I am using an 18' Firestik MU8R18Firestik MU8R18 Uncut/No trimming.
I used a SWR Meter w/ patch cable then removed it after tuning.
Am I suppose to get LED's on (3 of them) as if someone is transmitting even though nobody is? Or is this normal. If this is as good as it gets w/ this set-up then I will have to just deal with it for now then upgrade later. I guess I got what i paid for!
Here is a pic of the antenna mounted, it seems like more than half of it is above my roof line.

 

[GOT COPE?]

What squelch level does everyone place it at right when the noise disappears?

It varies quite a bit. You can turn it all the way down and you still wont be able to hear a factory radio from 15 miles away, yet you can turn it all the way up to block out all but the strongest and you'll still hear the guys runnin 2500 watts 20 miles away over the guys behind you. there is really no "place" on the squelch that works for every situation.

You guys think putting a noise filter in the main power line would help any?

Umm... post here www.cbradioforum.com

 

[Gargoyle]

As for the Coax I am using an 18' Firestik MU8R18Firestik MU8R18 Uncut/No trimming.
I used a SWR Meter w/ patch cable then removed it after tuning.
Am I suppose to get LED's on (3 of them) as if someone is transmitting even though nobody is? Or is this normal. If this is as good as it gets w/ this set-up then I will have to just deal with it for now then upgrade later. I guess I got what i paid for!
Here is a pic of the antenna mounted, it seems like more than half of it is above my roof line.

Interesting. I have been out of CBs for a while and did not know they made a connector-cable combination like that. Given that you have not cut the cable and it's original lenght is 18' (1/2 wave length) you should be well tuned. I would be a bit suspicious of the location though. The way an omni directional antena works is given a flat ground-plane you get an even radiation pattern surrounding the antenna. With a truck the ground plane is any metal and the best place to place the antenna and retain an omni pattern is smack in the middle. You have that well placed but your problem is that the antenna is not above the ground plane. So you end up with a distorted pattern--difficult to tell what it would look like but I would guess that you have a large lobe pointing backwards, a set of lobes to the side and a smaller lobe going forward. Speculation, but I would bet you can receive your buddy better (and he can hear you better) if he were behind you.
It is hard to say what the LED display is telling you. Not likely that there is unit calibration, is it transmitted power, reflected power, received power of a unit signal?? Your SWR meter is the best bet for calibrating the system but you have to change antenna positions, types, etc. to see if there is an improvement.
I will see if I can find some web sites to help you out. Try looking for mobil antanna info from IRRL.

 

[GOT COPE?]

To: anyone

http://community.webshots.com/user/wildyota5

see the 2 folders on my CB.

and www.cbradioforum.com is a great CB info site.

 

[Smiling_Jim]

NOS, Don't run two grounds...

Multiple grounds cause ground current loops in the system which brings the noise floor way up.

Your door lock solenoids have a lot of inductive kick, which radiates into your antenna. As one of the other posters said, modern cars have lot of electrical noise, and fuel pumps are the worst. If you can put a large cap across the fuel pump power going into the pump, that might help.

It doesn't surprise me that you can hear your door locks. That may mean your radio DC ground may be weak, or the antenna Shield ground may be weak. Try better grounds (short heavy wire to the body or frame), and a fuel pump capacitor.

 

[tacomotor]

Your situation is no different than anyone else that has ever installed a Cb in a vehicle with an electronic ignition. You are always going to have some ignition/ fuel pump noise. You can reduce it through grounding and such but there will always be some noise on your CB. You can try ferrite beads or chokes on some of your wires. They work but they are like voodoo, there seems to be no real rhyme or reason why they work sometimes and dont others. Check out what this guy did, http://www.k0bg.com/beadplace.html . Turning up your squelch to blank out the noise does not reduce the range that you will recieve someone elses signal. Because if their signal is not strong enough to get over the squelch it isnt strong enough to come in over your ignition noise either. I have 9 bars on my CB's meter. When I first installed it I got 7 bars of noise when the truck was running. This was not acceptable. I regrounded everything. No help. I put ferrite beads around the wiring near my fuel tank/ pump and reduced the noise from 7 to 4 or less. So the ferrite worked for me somewhat. You can also skin the plastic off of your coax about a quarter inch as near the antenna as possible and use solder a piece of copper strap or wire to the ground shield that you exposed and ground the copper strap/ wire to your truck chassis. You can get a great piece of ground strap by cutting up an old piece of coax and pulling the copper ground/ shield wire out of it. If you do it right it will be like a hollow woven copper strap. The bottom line is that you probably did everything right. If you cant live with the RF noise start trying these different things until you beat it. Good luck, John

 

[ripkinC]

Is there any way to get around buying a SWR meeter? I know their only like $15, but still for like a 1-2 time use? I have a Cobra 25, turned it on tonight, came in clear on the test. Running a K40 4.5'

 

[not2XS]

...If you can put a large cap across...

Actually, large caps do not suppress noise that well. They are usually of some wound foil construction, and so have enough equivalent series inductance to become significant at high frequencies. A much better choice would be a tiny 0.1uF ceramic cap for general use, or for real high frequency suppression a 0.01uF silver-mica type.

I put one across my power outlet, and stopped getting interference from my windshield-washer motor on my CB.

 

[TUFFTACO]

Try wearing a thong made of alluminum foil while talking on the cb. JUST KIDDING, I am having some guys at the cb shop tune mine with the swr meter. You guys have given me a world of info, I think I have the same cobra and a 2' fire stick being mounted on the custom light bar that is being installed, and the cobra is going in an overhead console with a switch pannel for all my lights. THINK I'M GONNA HAVE PROBLEMS........