Meter And Engine Noise Problems

[cdresmondo]

Hi all this is my first thread here.
I have three questions:

1.) I checked the swr with the meter on my cb, it reads about 1.4. Thats good but when I change it over to S/RF and I key up the mic it jumps up to 3(swr) or 8db. Any ideas why? I really don't want to mess up my cb.

2.) I get a lot of "engine noise" ( ign., alt. wine, windows, and a/c), would a good inline power filter work for this and if so which one is best. I feel like I get some fuel pump noise because of the hum in the speaker on accel, would a better coax fix this? ( I have radioshack's RG-5

3.) I was thinking of getting a power mic do you get better range with these, or are they a complete waste of money?

By the way I have a Cobra 29ltd bc with a 20' coax to a 102" whip anteena. Thanks for all the help in advance...

[kd5drx]

Originally Posted by cdresmondo

Hi all this is my first thread here.
I have three questions:

1.) I checked the swr with the meter on my cb, it reads about 1.4. Thats good but when I change it over to S/RF and I key up the mic it jumps up to 3(swr) or 8db. Any ideas why? I really don't want to mess up my cb.

2.) I get a lot of "engine noise" ( ign., alt. wine, windows, and a/c), would a good inline power filter work for this and if so which one is best. I feel like I get some fuel pump noise because of the hum in the speaker on accel, would a better coax fix this? ( I have radioshack's RG-5

3.) I was thinking of getting a power mic do you get better range with these, or are they a complete waste of money?

By the way I have a Cobra 29ltd bc with a 20' coax to a 102" whip anteena. Thanks for all the help in advance...

there is nothing wrong with your system the meter is doing what it is supposed to do in that Mode of operation. S/RF stands for signal receive and froward another words your transmit signal and your receive signal. the noise check your grounds and hook you radio direct to the battery for the hot wire and as close to the set as you can for the ground. and when you ran your coax is it layed out in a straight line or coiled up if its coiled make sure its not smaller than 18 inch coils and try not to wrap it around anything metal. and of course check every thing for good ground before you go to messing with filters. Then if you still have noise you need to isolate the cause of it is it comeing in on the antenna or the power. thats another topic all in its self.

[cdresmondo]

I do have my pos. and neg. ran to my battery, after what you said about the ground I will shorten it. You said try not to touch the coax to metal, my coax is ran from the antenna along the frame with the other wires through a plugged whole in the floor board coiled up there then connected to my cb. Should I run it differently? Maybe through the back hatch under the carpet? One more thing if you could give me some suggestions on how to isolate the noise that would be great.Thanks!!!!!!!!

[Red Fox]

Often we would avoid coiling the coax excess and just jumble it under the seat or wherever...that would keep it from becoming a choke coil and picking up junk from the truck.
The meter on the radio isn't accurate enough to set up an antenna; it's just there to let you know if something has gone wrong. Radshak has a little meter for around $30 that works well enough. Good to have.

[kd5drx]

Yes it would be better to run your coax under the carpet and away from Electric wires. DC is not real bad about noise but there is some there. To isolate the noise turn your car on and set your radio to where you are getting the noise then un plug the antenna from the radio if the noise goes away it is coming from the antenna input meaning something in or around the car is generating the noise. If the noise is still there it will be comeing from the power source some how and a filter will help. it its coming in thru the antenna then you have to start by iliminating one item at a time till you find the problem piece. Usually altinator or fuel pump 2 most common.

[Red Fox]

Ack! Good call, Kd: I'm way out of practice!
Actually, I set up that big homemade stick on the truck about 5-6 years ago, put in my little hotrod uniden with the TS670 footwarmer and haven't had to touch anything since; it's still running flat.
One reason is that I use electrician's NoOx on all connections outside of the radio. They never go bad. It's great on battery posts too.

[cdresmondo]

Ok well i unplugged the coax from the back of the radio, all the noise stopped even people talking(i did this at a truck stop on channels 1,19,20 and 40. same results on all 4 channels). With that being said I assume I have alternator and/or fuel pump noise. How do I decide which one? Something I have noticed in the past on my am/fm radio, my am stations have alternator wine noise... But the noise i am getting now is a wine with accelerating and constant "LOUD" static when cranked up and while running... only people with "big ole radios" get through while driving.

[Red Fox]

Unplug the coax from the antenna and see if it's still there. If so, you have it being picked up by the coax, not the antenna. To be sure of that, unplug again from the radio end and stick a knife blade in the center hole of the connector. You should be able to hear (not transmit) with just a knife blade for an antenna, and not pick up the truck noise. If it's still there, it's in the power cables, which ALSO should be independently routed if possible and away also from stereo wiring. This of course, isn't always possible.
If hearing on a knife blade works and the static is gone, you have a bad antenna or coax most likely. Also, check to see if it's the right coax for your number of antennas.
Hope this helps.

[cdresmondo]

When I unplugged the coax from the antenna there is very little static (so low that you have to turn it all the way up and have your ear with in 1 foot from the cb speaker just to hear it). Also when I put the knife in the back of the radio I hear the alternator whine but not that "LOUD" static... Does all this mean I nead to put a noise capacitor on the alternator and get better coax that doesn't pick up the extra noise? If so what coax if best for my single 102" steel whip.

[Red Fox]

I think it's 50 ohm coax for the single? (guys correct me, I use military FAT stuff)
You're using a 102? If it's not picking up the static with the antenna disconnected, it's the coax. (we now know it's not the power cables or radio)
102's are long and wind up near the truck grounds, and that can pick up stuff; also lower your SWR. I can't picture a 102 on a big truck, really; no place to mount it free of the truck. This may be your whole problem, but a cap on the alternator wouldn't hurt either. Make your am radio quieter too. You're getting close.