CB feedback

We did not measure mine and I have a fire stick at the rear of my runner. I can be way out of site, over hills, and still transmit and pick up people way in the back. The guy at the cb shop left me 1 coil in case I relocate my antena.

 

Cable is recommended to be cut in lengths divisible by three for impedance reasons (ohms per foot). The radio is looking for a certain impedance, or at least a harmonic of a certain impedance, in order to work most efficiently. Yes, you can have a non-3-foot-length cable and still have the radio work, but now you're just making the radio work against itself when, really, it's easy to avoid doing so. This is how it has been explained to me by several knowledgeable radio techs, and a few not-so-knowledgeable ones.
As for location, the antenna doesn't damn care where it is: front of the truck, back of the truck, the sides, mirrors, roof, your neighbor's house, Uncle Burt's ears (so long as Uncle Burt's ears have a good ground). It just wants two things: proper ground, and an unobstructed view. Assuming you have or can get a good ground, then location is really all about personal preference, keeping in mind you want as much unobstructed, open space surrounding it as possible. The roof is the hands-down best spot for any length antenna. If you have a 2-foot antenna, mounting on the rear bumper or in the bed or on the bed rail right next to the cab are about as bad a spot as you can choose; if you have a six-foot antenna, your options open up much more dramatically, because it can reach above most of the truck. Of course, keep this in mind: Most of your transmission signal leaves out the base of the antenna (receive from the tip), so if you want a pretty good reach, make sure the base is unobstructed -- again, the roof is best. This is why Big Trucks mount theirs on the mirrors -- look at a Big Truck and tell me a better location that is both high enough to reach over the trailer and unobstructed enough to get the signal out. Personally, I like making things do as many useful things as I can, CB antennas being no exception -- as such, I mount mine where I can use it as a guide to where my truck is, like the front right bumper corner (for obstacle approach).

 

Here are some pics... I'm still getting feedback and am about to throw the fucking out the window...



im back to thinking the feedback is coming in through the power line to the cb, but wiring it to the battery or anywhere else doesn't change it. my ground to the radio is wired directly to the battery terminal..

 

well I have a bunch of coax coiled up under the kick board, but have no idea how to reconnect something like that if I cut it. and im not entirely sure that would cause feedback when I use electrical things in my truck. I bought a matchmaker on ebay, when it comes im planning to use the cb antenna as my am/fm/cb antenna in the stock location, maybe thatll help.

 

Surprisingly these work to knock down some of the noise.

http://radioproshop.com/filters/ns50.htm

At least it did on my Ham multi band radio

 

yea, I hear mixed things about those. im going to try another cb radio and see if that takes care of it. my uniden pro 510XL is so basic that its prob just picking up whatever the fuck comes across its frequency range, as it has no RF suppression.

 

Rather than run the ground directly to the coax connector, try running it to the bolts holding the 90* bracket on. Also, use larger AWG wire -- 12 as a minimum. While I'll bet it is, are you *sure* that bolt you chose is a good ground? You might try adding some toothed washers to both connectors of your grounding wire.
Do you have a pic of the underside of the bracket, where the coax connects? I'd be interested to see what your washer stack is there. Perhaps an exploded view (disassemble the whole thing and lay it out in order of installation)?
If following the above steps (larger AWG wire, dead-sure of the ground, toothed washers, connecting the ground wire to the bracket and not the connector) doesn't solve or at least significantly improve your situation, try some of these:
Unwind your coax and let it have as much breathing room as possible. It's possible that the sheer number of loops and parallel winds is not only causing an electro-magnetic feedback loop, but may also be picking up interference from the truck wiring that's in there.
Move your antenna location to someplace significantly different (say, front bumper, hood hinge, rear bumper, roof). It's possible this is just a hands-down bad location; it's also possible that it's too close to the cab, and you're getting a bounce-back feedback effect (rare, but happens).
Try choosing a different grounding bolt. The best would be if you could find a stock grounding bolt (will have wires coming from under it), because you'll KNOW it's good. It's possible the bolt you chose isn't as grounded as you think (it is, after all, a body mounting bolt not intended for electrical conductivity).
Try a different antenna. I say this because I was experiencing a constant 3.0:1 SWR (indicative of a bad ground), and I was dead positive my old Astatik 3K was fine......until I swapped it for a brand-spankin' new Firestik, and suddenly everything worked like it should.
Try a different, SHORTER coax. It's possible this one is bad, is too long (I've never heard of a 21' coax), or maybe is broken internally from your packing job under the door sill.
If all else fails, and you've done all this, try moving the power locations. I doubt this is it, but it is entirely possible. Hook it directly to the battery to start with, then start moving the negative power wire around to different grounds. You might also try adding a grounding wire from the body of the radio to a good grounding location in the truck (so that you effectively have two negative/ground wires for the radio).
And if you have done all this and you're still not seeing any improvement, I would tend to say your grounding issue has fried the internals of your radio. Have a shop look at it, or swap it out for another known good radio. If you were running for any kind of time with the antenna signal and ground wires shorted, you may have damaged the radio itself.

Something to keep in mind during all this: Try everything one at a time so you can isolate the culprit. Do it all in a temporary manner so that once you find the problem, you can then permanently install the system with that one issue addressed -- don't do testing in a "permanent install" mindset, because you'll only get frustrated that you have to keep tearing it all down and re-doing it. While you're dong all this step-by-step testing, you should have all kinds of wires dangling out of all kinds of places in your truck, with all kinds of doors open (test operation with doors closed, however. It can make a difference). You may even have the radio sitting on your seat, upside down and open, so that you can try out different power/grounding combinations.

 

the ground wire is running from a bolt on the 90 degree mount to that body bolt for ground. not sure if its good or not, just saw some other members do it, and it was a pain in the ass to get it there so I hope its a good ground... I unraveled the coax and it still feeds back, no difference

ill try some of the other suggestions and report back.

 

Also, how is your mic cable? Could be another possibility.

 

Loops wont cause a" feedback" issue, the loops or wound coil would help to eliminate any feedback or stray RF, this is called a Coax balun or an ugly balun and is used often in ham radio.
Example: http://www.hamuniverse.com/balun.html

After looking at your pics I'd say make a bigger better ground wire and go directly to the frame. As far as material try to find some braided copper like from here: http://www.mcmaster.com/#braided-straps/=kgpsmn

I run my HF antenna(s) on the back bed pillar and run an extra big strap from the pillar to the frame, on 10 meters ( ham frequencies near CB) I have a dead flat match or 1.1:1.

btw, I use that filter on my ham radio and it knocked down alot of issues.

Also you wont make all of it go away but you can bring it down a few nothces

 

Honestly man I think it's where you have it mounted I've tried to mount it in the bed twice with no luck. After moving it to The front it's fine. Even had my ground on the same bolt. It's just not enough back there.

 

yes in some cases location can make a difference with SWR, as far as Vehicle EMI not really.

 

Have you looked at Famous Fabrication's new bed mount for the antenna? I think that is very promising for getting it right on a Tacoma. I have probably installed over 200 CB's in my lifetime and I have never ever had one give me fits like the damned Taco does! The bed is just not conducive to providing a good ground plane. Perhaps grounding the mount helps some, but the "plastic" bed just doesn't create the plane needed. I know there is a lot of talk here about grounding, etc but that is only a part of the battle. The antenna needs a ground plane to effectively make up for the wavelength that the antenna doesn't have.

The best luck that I have had up until Derek provided this new mount has been to use a Wilson wip antenna on the cab. That is the best I have ever gotten the SWR on a Tacoma and it was around .2!

As far as coax, every single FJ that I have ever installed a CB in gets the 18ft. It comes up a bit short for a roof mount radio, but its easy to add the extra 3ft. If you do have extra, that doesn't hurt a single thing as long as the excess is stowed properly. Never roll it into a coil. You want to stow in coiled like a flat bow, not a round coil. Yes, it does make a difference.

On your feedback issue... do you mean static noise from the truck? Any good filter capacitor setup will fix that. Sometimes you may hear a little noise from things like the A-Trac or antiskid if you are braking hard but the rest of it should never break the squelch. If a CB is installed properly, and operated properly you should not hear a peep out of that box unless someone is talking to you. That applies more on the trail because in real life you'll get truckers and the other 100 asshats that live on the bands to harass people.

 

Some of your statements are true, however the "ground plane" in a vehicle is not, some basics: http://www.k0bg.com/gpnotes.html

The tunable wave length of an antenna dictates radiation take off angles only.

As far as the "feedback" statement, he means if the transceiver is in receive and an onboard device is activated that uses the common DC power triggers the receiver, or Vehicle EMI, the filter is the way to go in order to knock down some of this but not all.

 

http://www.quest4.org/radio/reducing_noise_interference.htm

 

Okay, here's the basics. A CB radio requires at least three grounds - radio electrical ground, coax ground, and the antenna's RF ground (called a ground plane - read on for more). The first two are fairly self-explanatory, except perhaps the coax ground since the truck's bed is a fiberglass composite, not metal. The coax (antenna mount) needs to be grounded to metal, at a point closest to the antenna to also provide an RF ground.

To understand the latter (RF ground or ground plane), remember that a CB antenna is basically a dipole antenna. A dipole antenna is balanced design with two symmetrical conductors (wires or rods/radials), electrically fed in the center by coax, ladder-line, or similar. In a vehicle, to make the overall antenna shorter, one of those radials are removed, with the metal body of vehicle itself (or a similar large metal surface) providing the function of that missing radial.

To obtain a proper ground plane, you need to mount the antenna on a large, flat, metal surface (a size equal to 1/4th the radio wavelength is ideal, but seldom possible with most vehicles except large trucks). The antenna may (and indeed often does) work with less (near such a surface, for example), but not as efficiently as it would with a truly proper ground plane.

Examples of good (large metal) mounting surfaces (for a ground plane) include either side of the hood (good, but off-centered so not great), the center of the roof (excellent), or the center of a large, metal, toolbox in the truck's bed (very good). In a car/sedan, the center of a trunk is usually good if the mounting surface area is large enough (not a small trunk in a very compact car, for example).

Proper installation of the antenna can significantly increase transmission range, slightly lower (a few decibels) background noise on the radio channel, and reduce electrical noise picked up by either the coax or antenna.

If you absolutely cannot install the antenna properly (no metal surface, etc), consider a no-ground plane antenna like those commonly used on fiberglass boats or motorhomes. These completely eliminate the need for a metal mounting surface for either the coax or antenna. The missing radial in these dipole antennas (see paragraph two above) is provided by a section of coax rolled back along the coax's plastic sleeve (either inside or outside & covered). Do not cut this coax. Another option is trucker-style antennas, which reduce (not eliminate) the need for an ideal mounting surface.

My antenna (a Wilson 2000 trucker, with an 18" extension to get it above the roof line) mounts in the middle of a gull-wing-style bed toolbox, between the two lids opening from the sides. A spring at the bottom of the extension reduces strain on the toolbox and antenna. That large metal toolbox provides both the coax ground and a sufficient ground plane - and holds tools & junk as well (multiple birds with one stone). It's an expensive option, though.

 

Please don't take this as a smart ass answer, but I beg to differ (somewhat).

For you to get a full wavelength antenna for CB use, the thing would have to be approx 33ft tall. Even a true quarter wave is around 8ft. You make up that difference in the ground plane. Agree or no?

If you are saying you don't need a ground plane, then why in even commercial AM transmission towers do they lay ground plane radials in the earth beneath the antenna? So again I will state that to have an effective and efficient antenna you need a decent ground plane. (and the antenna needs to be obstruction free not 3/4 of its length hiding behind the cab of the truck)

 

What he said. cept for the NGP antenna. I hate those too, but that's just me. LOL

I hope to get one of the new tailgate mounts installed and report back on what I find as far as SWR goes.

 

From an experiential point of view, Nick and Stewart are correct. Also from a thinking-it-through-using-common-sense point of view.
The antenna wants a large hunk of metal it can ground to. A simple grounding wire isn't going to work (it can be a backup for people like me who didn't want to remove powdercoat over a big hunk of metal the antenna is mounted to). I know I never hinted at this, but I was thinking it in the back of my head the whole time, and should have been more clear.
Get it out of the plastic bed and onto something metal. Also get it away from obstructions (like the back of your cab) -- the more antenna you have above the truck the better the performance.

As far as Stewart's claims about needing a huge flat surface area, this just does not agree with actual reality. In theory, yes, this is ideal. But I challenge you to find me anyone that actually does that (ok, so there are plenty of people who use a magnet mount on top of their roof) -- keeping in mind the number of Big Trucks there are, and how many you've seen mount the antenna anywhere other than the mirrors (Big Trucks are about half fiberglass and half aluminum -- the horizontal surfaces and the front clip are all fiberglass, while the cab and sleeper are aluminum). I'm getting a better-than-perfect 1.05:1 SWR with my Firestick II mounted via pipe clamps on the hoop of my powdercoated ARB bumper.