Help! Antenna Behind Cab Mount and Ground

I think you need to focus some more time on researching and checking your ground with a multi-meter. You said you "touched the two ends together and got 1.8", if you are referring to the 2 meter leads it should be 0 or infinity.

Maybe study a little more on checking swr. Are you coming up long or short?

 

Ok, so i watched a couple of videos on checking continuity with a multi-meter. I have continuity between the mount and the ground.

Holding the tips of the red and black probes together got me a reading of around 1.8.

Holding the red probe to the mount and the black probe to the ground read around 1.8.

Holding the red and black probes to the mount read around 1.8.

Holding the red probe on the positive of the coax and the black on the negative of the coax showed no reading.

These tests were conducted with the multi-meter on the 200 Ohm setting.


What do you mean by coming up long or short on the SWR?

Mostly to be used for wheeling. It will most likely not be powered on any other time.

 

Just a quickee that you might have already mentioned or done. Are you certain that the impedance of the transmitter and the impedance of the antenna match? Your CB antenna looks pretty short, which means generally there is some sort of loading coil involved to match impedance at the right frequency (11 meters I assume). I am sure you know that antennas are not simply "plug and play". I haven't done CB in almost 50 years now (I was young when the CB craze hit in the 60's and there was way more traffic there than on the typical ham bands I watched). Optimal antenna length is 1/4 wave in general. Pretty long (11 meters / 4 = roughly 8' long). I used one of those for years, mounted on top of the rear quarter panel of my car. Learned REAL QUICK to not drive up into a drive-in eatery with fluorescent light tubes overhead. Took out about 30 one afternoon and kept wondering what all that damned popping was behind me.

In any case, 102" long is a bit much probably. But there are ways to get that kind of effective length with a loading coil built in. But you have to be careful. The loading coil has to be above the top of the vehicle, because you are already losing efficiency with a sub-8' antenna length. If you mount it behind the cab, you are not going to radiate much of a signal in the forward direction at all.

For your case, since I can't really tell, I can only assume you have a top-loaded glass antenna? You might want to take it to a good CB shop and have them run a quick test. They can identify a broken/bad loading coil, which will certainly completely wreck your SWR. My dad used a magnetic bottom-loaded antenna for years. He started by sticking it on the back of the body right in front of the trunk lid. Two problems. He could talk to people in the backward 180 degree arc, but not forward. Opening and closing the trunk kept banging the loading coil and eventually his transmission range was maybe one mile or so. He bought another and I explained why it ought to go on the roof, and he was happy after that.

The SWR meter is useful for detecting you have a problem, I had much better SWR numbers with the thick coax than with the much easier to use thin coax. Minimize connections. I had the PL connector at the radio, and one at the antenna. Every connection adds to the problem.

Now a couple of notes. Your antenna location is absolutely horrible. Unfortunately. If you are not a radio techie, look up "ground plane" which is what most CB antennas need. Ideal location is dead center on top of the cab. This gives you a good ground plane in all directions (I'm not going to go into what this is about, but if you have questions, feel free to ask). If you stick the antenna on the back side of the top, you get much better transmission forward, and much poorer transmission to the rear. The opposite for putting on the front edge right behind the windshield. For your installation, on the edge of the bed, you have (a) zero ground plane, and (b) almost zero signal transmitted forward since the truck cab is in the way. By far the best solution is a good top-loaded antenna with a magnetic base, stuck dead center on the roof. Anywhere else is a compromise.

Also, good loaded antennas have a tuning adjustment in the coil, since the optimal antenna "length" is slightly different for every CB channel. If you look up how to tune the antenna, you'll see that you should check the SWR on the highest and lowest channels you will use. Adjust the length until the SWR is equal on both.

With that said, good luck finding it. Sorry for a bit of rambling here and there. But as you can see there is more to it than just plugging 'em up and going. You particularly need to find a better mounting place with flat metal surface in all directions below the mount. In the 11 meter band, power is limited. In the ham world, we can use whatever power we want in some of the bands. Enough that you can keep people from leaning against your car while you are parked, if you want. Just key the mike with a 500+ watt transmitter and light 'em up.

 

For CB? Max = 4 watts by federal law. I think 300w would be AMPLE.

 

I think he was probably talking about tuning. If you want to cover all 40 cb channels equally, check the SWR on channel 1 (you need to calibrate the SWR meter after you switch). Then check the SWR on channel 40. One will likely be higher than the other (ideal would be equal SWR on both ends of the band). If the SWR is higher at chan 40, then you want to shorten the antenna a bit. If it is higher at channel 1, lengthen it. Slowly. Until you match the two values.

I've burned up a good transmitter by operating with a (unknown) high SWR, so caution is needed. Over 2.0 is pretty "iffy" for performance and radio longevity.

 

Ok your ground sounds good and you aren't shorting the positive to ground

Short or long, with swr refers to the comparison of Ch1 swr and Ch40 swr. This will tell you if you need to adjust your antenna longer or shorter to have good swr on all channels.
Here's a good, albeit long, article on swr. The more pertinent section is below.
http://www.firestik.com/Meas-SWR.htm

 

That's hilarious about the lights popping.

I am not sure about the impedance of the transmitter or antenna. I kind of assumed that they were in fact plun-n-play.

Since you mention connectors, I did have to install this little guy in order to get the radio mounted:


So I'm going from radio, to this "L" adapter, to the coax that connects to the mount.

So we're on the same wavelength here .

Just wanted to make sure that wouldn't play a role in anything sending or receiving.

I'll check tonight and see what that shows.


Thank you all for your help with this. I'd buy you a beer if you were in the area. I know I'm not the only person with these problems, so hopefully this will be a good guide for people in the future. I know it can be done!

 

I just hate we can't be more help without being local. I'll hold you to that beer if I'm ever in town. In the mean time if anyone local to me wants to buy me a beer I'm game.

 

I just realized it says you are in Boone. My wife's family lives there, so we are that way at least once a year. We might have to meet up at the Boone Saloon.

 

Awesome! Though I used to go to school there. Sadly I had to leave to get a job and pay for my addictions... I mean hobbies.
I do love going back to visit and hike!

 

hi, I'm a newb going through a CB install myself.

from the pic it seems that your ground wire is bolted to your mount, so effectively you are grounding through your bracket, right? do you think maybe the bracket itself is the issue?

on mine I am using that same type of connector you have but mine is on the antenna stud itself, hopefully for better contact (hopefully, like I said... noob here. guess I see when I get it all connected...!)

 

Please reference the top left pic noting the Hot and Ground. You might be close to grounding out the hot with your ring connector.

 

hmm.. see what you mean. time to rethink, thanks!

do you have any suggestions for when the bracket isn't grounded?

 

Just take it apart and look at part E, as in this picture, from the top-down and make sure the ring connector is not touching the Hot part. Post a picture please.

 

another item i don't think that has been mentioned yet. I understand you borrowed an SWR meter. On the SWR meter should be marked a frequency range. Make sure it is designed for 10-30MHZ (CB band) and not VHF (30-300MHz).

 

I don't think it's the mount because I have continuity between the mount and my ground.

I don't see the frequency range, but it's the exact model that I used the picture in the OP. Workman swr-2t borrowed from another forum member who used it to tune his cb.


I'm hoping to pick up troubleshooting this today. Work and house projects have taken priority.

 

So I got a chance to play around last night. I moved the antenna around quite a bit and also used a heavier wire brush on a dewalt corded drill to strip away more of the protective coating on the frame at the ground. Net result: no change.

Moving the antenna around seemed to have zero effect either. I also tried using a 2' Firestik II to see if I got any different readings vs. the 3' generic antenna that I was using before. I recorded the exact same SWR on both antennas.

I moved the antenna back to the side rail where I previously had a reading of 3:1 since that was better than the ~3.5:1 that I was getting on the rail behind the cab. Unfortunately, I'm still at roughly 3.5:1.

Thoughts?

 

wrong impedance cable or damaged transmitter.

 

Coax connection at radio as well. Posts above focus on the Antenna connection, but the connection at the radio is just as important. If the coax is bent sharply, breaking the conductors inside or rubbed through anywhere so the ground is rubbing against the truck metal, even if it is painted can cause additional problems as well.

 

Forgive the newb-ness. What do you mean by impedance cable? By damaged transmitter, do you mean the radio itself is bad?

Coax is not bent. There is an "L" connector in there to avoid a sharp bend in the cable. It was also a new cable, and I have no reason to believe it is bad or damaged in any way.