I just did Bob's rear hatch mount antenna install and now I'm getting lots of RF noise when I have the truck running, but none when the engine is off. I'm using the exact same antenna setup as Bob's, but with a Cobra 18 WX STII. Here's the strange part: When I open the hatch or hold onto the top of the antenna, the noise goes away, but returns when I close the hatch or let go of the antenna. The noise is steady across all channels and is very annoying, especially when trying to listen to chatter on the highway. I've tried re-routing the antenna wire and there's no change.

I'm wondering if at this point the radio itself could be to blame, especially since it doesn't have an RF gain control. If anyone has any suggestions, please let me know before I go and pick up a Uniden PRO520xl as a replacement.

 

Here is some very good CB info. The noise is probably being caused by your truck. Not the CB.

 

I just tried to check out the article and I have have a log in to see it. When I try to register, the site says that registration is closed. Is there a different link to it or way to post it?

 

When the registration page comes up, click on "search" and it will let you into the search for keyword/author page. You don't need to register. Sounds like maybe you're not grounded or, if you are grounded, maybe your ground isn't sufficient enough or you have a resistive ground. Your ground wire shouldn't be longer than 18". I used a neg. battery cable as a ground wire and it worked great with my 4ft Firestick.

 

The antenna must be grounded, well grounded and that means well grounded at RF frequencies. Have you tested the SWR with a meter yet? If the antenna is not properly grounded, the SWR will also be very high and you risk frying the transmit section of the radio if you use it like that for long. I have some antenna mounting/grounding info on my page as well as a link to Firestik's web page, they have an excellent tech section about antenna grounding. One thing I tried that pointed to the grounding problem I was experiencing (I had a good DC ground as meausured by a meter) was to clamp a jumper cable to the antenna bracket and to a clean ground on the frame. I noticed that dropped my SWR reading, so led me to the conclusion grounding was an issue.

 

Sorry about the link guys. Heres the article.

Radio FAQ’s and tips
Compiled by Tim A. King, Jr.
Extra Class Amateur Radio Callsign AG4RZ


The purpose of the following list is to provide information and answers to some of the common questions off road enthusiasts have regarding CB radio installation and operation. It is by no means complete, nor is it guaranteed to solve all your problems. If anyone can think of anything that needs to be added please let me know.


*WHAT KIND OF RANGE CAN I EXPECT FROM MY MOBILE CB?
"Generally Speaking" range for a mobile CB Radio could be anywhere from 1 to 20 Miles or more, depending on terrain, type of antennas used & other factors. The "typical" range to expect from a mobile CB with a good antenna is about 2 to 5 miles, you will actually get more or less than these numbers in certain areas & terrain, & as you drive.

*WHAT DO THE RF & MIKE GAIN CONTROLS DO?
Mike Gain (DynaMike) is your mike's "volume control", & can be lowered to reduce background noise, or if your voice is really loud. The RF Gain control can be thought of as a "Receive Distance Control", by turning it down you can reduce the radio's sensitivity to distant chatter, noise & signals that are too weak to reach. The Better CB's will usually have both of these controls.

*WHY DOES THERE SEEM TO BE MORE STATIC ON CB CHANNELS THAN WHAT I HEAR ON OTHER TYPES OF RADIOS?
Just like you car Stereo's AM/FM stations, where the "AM" has more interference than the "FM", CB channels are transmitted & received using an "AM" mode. Other Radios like FRS, GMRS, Police scanners etc all receive in "FM" mode. Again, with CB, just like switching to "AM" on your car stereo, you will notice more static than when on FM. Look for CB Radios that include a Noise Blanker ("NB") switch, which helps minimize some of the noise better than standard CB's that have no noise filters, or just an Automatic Noise Limiter "ANL" switch.

WHAT IS SIDEBAND?
"Single Side Band" (SSB) is a mode capability found in higher-end CB Radios. You will have access to the upper & lower Side band Modes (USB, LSB), In addition to the "Regular" (AM) mode on each of the 40 channels. When switched to side band, each receive signal must be "fine tuned" in with the clarifier or voice lock control found on the SSB CB radio, otherwise people will sound garbled or distorted. Keep in mind that when switched to a side band, you can only communicate with other CB'ers that have that capability. You can usually expect an increase in range, & less noise than on the "standard" AM 40 channels. SSB is the primary mode of voice communication for Amateur Radio operators.

WHAT IS THE BEST ANTENNA FOR MY MOBILE CB RADIO?
This is tough to answer, but here are some general guidelines & "Rules of thumb". First, the taller the antenna, the better it will work. Mount your antenna as high as possible on the vehicle, & try to get at least 50% of it over the roofline. Usually, all else being equal, the tallest, longest antenna you are comfortable with, mounted as high as possible, will give the best performance. For example, mounting a new 4-ft CB antenna where you had a 2 footer, will usually give better results. It wouldn't matter what "brand name", color or style the 2-ft antenna was. CB antennas that are less than 3 feet tall, those that "stick to the glass", & AM/FM/CB "combo" antennas & adapters generally do not give good performance, they are bought & sold for "convenience" reasons only. I will ask that if you buy an antenna, please buy one with a tunable tip, if you decide not to buy the 108” whip. The tunable tip will make it A LOT easier for you to get your SWR set correctly.




WHAT IS "SWR" & ANTENNA TUNING?
SWR is a measure of how well your antenna is "matched" or "tuned" to operate at CB frequencies, & to your vehicle. CB & other "transmit" antennas need to be tuned to operate or transmit correctly & efficiently. If severely "out of tune" (or having a poor SWR reading), damage to the transmitter can result. While most good CB antennas, when mounted & grounded correctly as the maker intended, will usually have a "safe SWR", keep in mind that it is still a good idea to check & optimize your SWR reading. Regardless of Mfg.’s claims, there really is no way to "Factory pretune" antennas for CB frequencies. The same exact antenna can actually give different SWR Readings when mounted on different vehicles or even in different spots on the same vehicle!

WHY DO SOME RADIO’S CLAIM TO HAVE MORE POWER THAN THE FCC LEGALLY ALLOWS (4 WATTS)?
A few CB's seem to claim 5, or even "7 watts of output" on the box. This is misleading, it actually refers to the audio power sent to it's built in speaker, "input" power, or some other nonsense that has nothing to do with the transmit output to the antenna, which is still 4w or less in that radio. In fact, it is usually the small, thin "cheaper" bottom-end CB radios & "Walkie Talkies" that make these claims!

HOW DO I INSTALL MY RADIO?
Well, this is a matter of personal preference. First, there are some guidelines to follow:
1. Make your installation SAFE! Don’t leave loose wires hanging; don’t mount the CB where the unit itself or the mike will interfere with vehicle controls.
2. Use safe wiring practices..PLEASE don’t twist wires together and tape them up with masking tape. (I have seen this done) Use solder and electrical tape, or crimp your connections.
3. Make sure the radio is solidly mounted to something metal…don’t just screw a radio to the plastic dash and expect it to stay there. Remember, your 4WD takes a beating.
4. Be sure to put the radio where you can see it as well as operate its controls easily.

HOW LONG DOES MY ANTENNA CABLE NEED TO BE?
Ok…here is another tricky one…listen closely…for a mobile installation the cable needs to be long enough to reach from the radio to the antenna, with a couple feet of slack. Period. End of discussion.
(WARNING: TECHNICAL DISCUSSION FOLLOWS)
Now, as you all know, there are exceptions to every rule, and I do not want anyone to think I don’t know what I am talking about, so this will require some explanation. There are times that the length of feedline matters. Sometimes (mainly when dealing with fixed station installations), it is possible to use the feedline (coax, antenna cable, ladder line, etc, etc.) to tune the antenna system. Now, this will not matter in mobile installations as much, because if you buy a tunable tip antenna, you will have all the adjustment you need. If anyone wants to get more in depth about this, let me know, and I will be happy to explain it to you. In the meantime, just trust me…in all my years of mobile radio installation, I have NEVER adjusted the feedline length to tune an antenna system in a vehicle.


HOW DO I GET A GOOD SOUND FROM MY RADIO?
Don’t yell into the mike! Speak in a normal voice, and hold the mike away from your mouth a couple of inches. The whole point of having the radio is so you can talk to the rest of the group…If you yell into the mike, or try to “eat” it, you will sound garbled and distorted, making it harder for someone to understand you. Careful setting of the “Mike Gain” (Dynamike) control will also help with this.









WHAT IS ALL THIS IGNITION NOISE/ALTERNATOR NOISE I HEAR?
Well, that’s a tough problem to solve. First, the best way to start getting rid of noise is through a proper installation. Use power leads just long enough to get from the battery to the radio. Yes, you need to run the power straight from the battery…the battery offers some filtering because of its internal impedance. Make sure the ground is also connected at the battery. I know it means more wire to run, but it eliminates ground loops and helps to get rid of noise. SAFTEY MOTE: PLEASE fuse BOTH leads going to the battery! If you don’t, you could run the risk of a fire in the vehicle!!

HOW DO I GET RID OF THIS NOISE?
Another hard question. Make sure your complete ignition system is in good shape. Check the wires, plugs, cap, rotor, everything. Use resistor plugs and wires, and make sure all the connections are secure. Make sure the cap doesn’t show any signs of arcing. Noise in a vehicle is the hardest thing to track down, so be prepared to spend some time chasing this stuff down. USE FILTERS AS A LAST RESORT!!! Filters are like Band-Aids….if you don’t stop the cause, they don’t do a lot of good. As an example, when I bought my Jeep, I installed some amateur gear, and had noise. After checking a little, I discovered that the wire from the coil to the distributor wasn’t making good connection at the coil end. Actually, the connection on the coil was rusted, and the wire was barely pushed on. I cleaned up the wire and connection, put a little Vaseline on it, and reconnected it. The ignition noise had disappeared. For alternator noise, make sure the connections are all secure and clean. Be sure that your ground straps are all in place…not just grounded to the engine block, but also from the battery to the frame, and the battery to the body. Sometimes you also need to bond each body panel together, and to the frame. Noise in a vehicle can be hard to get rid off, so don’t despair. For newer vehicles, the computer and electric fuel pump can be a source of noise as well. These are harder to solve, but if anyone suspects they have this problem, contact me and I will offer suggestions. These problems require a very technical approach, and go beyond the scope of a basic FAQ.

I know this isn’t all-inclusive, but I hope this helps all of you. If you have any specific questions, let me know and I will try to include them in this list. This is by no means all-inclusive, but I hope it is a good start.

Created 14 May 2003

About the Author:

Tim King was born 20 May 1974, and grew up in rural North Carolina, where he entertained himself with electronics books and gadgets left over from his father’s teenage years. His interest in electronics and radio goes back to his pre-teen years, and he has rarely been without some sort of workbench to tinker with electronics. Trained by the US Army as an Avionics Technician, he spent nine years working on aircraft radios onboard Huey, Blackhawk, and Apache helicopters. He has served in Kuwait, Germany, Spain, and the Azores. Tim also worked in several car audio shops, installing high-end car stereo systems, as well as CB radios and business radios. Tim currently holds an Extra Class Amateur Radio license, Callsign AG4RZ, and is a past Vice President of the Forsyth Amateur Radio Club, an ARRL special service club dedicated to emergency communications and the furthering of the radio hobby.

 

Well, it looks like I found my problem. I troulbeshot oll the grounds and leads to the radio and found that it was grounding out though the antenna mount. I flipped the fire-ring on the mount so that it would ground better on the mount and no more noise except for a small amount of engine whine (to be expected). It should now tune down to 1.5 or lower. I'm so happy that I don't need a new radio and that I can now use Bob's antenna mod to its fullest!

 

Well, when I flipped the antenna wire I lost almost all reception and the SWR went through the roof when tested. When I flipped it back over my reception came back and I can get the reception down to about 1.6 across the channel range. But the rise in ambient noise returned, so I tried some experimentation. I made sure that the "FireWire" connector was tight on the mount and grounding properly. I even wired & grounded the CB straight to the battery, still no reduction in ambient noise and no further reduction in SWR, and I have the tuning tip cranked all the way out. Here are the other two issues that arrise with this:

• When I hold on to the antenna, as I move my hand up the antenna, the ambient noise delines until it disappears when my hand is at the top.
• The radio is grounding its power through the antenna cable so that even if I remove the main ground wire, it still operates by grounding out through the antenna mount.

Because of these two issues, I'm leaning more toward the radio being defective and not the antenna mount being bad. I've removed my Cobra and have ordered a Uniden Pro520xl from the Uniden site; it should arrive in the next week or so. Then I can test to see if my theory about a defective radio is correct. I'm going to be on travel for the next 2-3 weeks so I won't be able to work on this but if anyone has any ideas, please post them since I'll be online while I travel.