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Discussion Starter · #1 ·
I had to replace my antenna and with that, I got my SWR meter out. So this is the problem.

When I check channel 1 after calibration, the SWR goes all the way past 3.0. Same with channel 40. Did this ever happen to anyone?

So what could be wrong?

Any advice is appreciated.
 

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New antenna mount too? Like the below? If so, it is absolutely CRITICAL that it be assembled exactly as shown, pay extra attention to the white nylon insulated shoulder washer that belongs on top of the mounting bracket. Its sole job is important, it's there to prevent the antenna itself from being shorted direct to ground to the mounting bracket.

If that insulated shoulder washer is missing, broken, installed in the wrong position, not centered in the hole, upside-down, etc. your SWR will be over 3 since any of those will cause the antenna to be shorted directly to ground.

Another cause of an antenna shorted to ground is if the mounting hole in the bracket has too small of a diameter, that will cause the threads of the antenna to touch the bracket and short to ground through the bracket.

And measure/tune your antenna with your CB on ch 20 which is dead-center in the band. Once the antenna is tuned for the lowest possible SWR on 20 it will also have as low of an SWR as possible on channels 1 and 40.

I've installed/fixed/repaired a lot of antennas over the years, especially CB antennas on Jeeps, and the above issues cause 99.9% of the problems.
 

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Last time this happened to me, it was a bad Wilson antenna. What kind of antenna did you replace the old with?
 

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Could also be the antenna cable is pinched or damaged. A short in the coaxial connectors may also be the culprit behind abnormally high SWR readings. Issues with the coaxial cables are often identifiable by eye, such as severe bends or pinches. You should know that it's essential to use 50-ohm coax for single antennas and 75-ohm for dual. When all else fails, sometimes it's necessary to replace the coax cable because there's a failure inside the line.

Also could be a poorly grounded antenna mount or a bad ground plane. A large percentage of high SWR readings are caused by ground plane problems. It's a good idea to run ground straps from the body of your vehicle to the frame, doors, trunk -- everything except your dog. Running the shortest possible ground strap from the antenna to the chassis or your vehicle is generally a good solution for ground plane problems. Simply put, grounding everything that can be ground together will improve ground plane.

The deal with checking SWR's on channel 1 and 40 is to help determine the antenna length before fine tuning the SWR's

If the SWR on channel 40 is higher than that on channel 1, your antenna is too long.

If the SWR on channel 1 is higher than that on channel 40, your antenna is too short.

If you have good grounds a proper ground plane and length antenna you should be able to get the SWR's below 1.5:1. Every radio I've ran over the last 40 years has had 1.0:1 to 1.5:1 using those procedures above.
 

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Discussion Starter · #5 ·
Jerry/Kota

I replaced it with a 4' Firefly and then replaced the antenna spring with a Firestik SS-3H. So it does look like I messed up the reassembly, including the nylon washer. Thanks for the schematic Jerry!

Mudbug,

You brought up great points as well ... I just had my rusted frame replaced (which was how I snapped my old antenna - long story), so I think I also need to run ground straps, and it is quite possible I pinched/damaged the coax because we had to weld some parts onto the body to make the frame work.

Can you give me some pointers/ideas/'how to' on running ground straps?

Thanks to all three of you ... all your comments were spot on, and it was good to hear what I was sort of thinking ... now back to work. LOL
 

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Sure how and where is your antenna mounted?

Also be sure your mount and antenna grounds are clean paint free connections.

I have also seen antenna springs sometimes cause poor SWR readings.
 

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Discussion Starter · #7 ·
Mudbug, thanks for the assist on the ground straps to the frame. Any help is appreciated.

Regarding the antenna, I would like to use the existing antenna mount, since my previous antenna worked ... which is located here:
 

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No problems with where your mount is matter of fact mine is in the same place.

Pretty basic really, find a spot between the tub and frame to install a braided ground strap or two.

If there isn't a strap between the the tub and hood do that also.

Between the tub and tailgate.

If your radio mount is not mounted into metal then a ground strap from the radio body to the tub.

It would be optimal to run straps from the doors to the tub. Most of us do doors on/off sometimes frequently so I wouldn't worry about those. Wouldn't hurt to keep the the hinge pins clean and rust free though.

The braided ground straps should be a minimum of 1/2" wide, all connections should be rust and paint free. Once you have cleaned the area around the connection, made the connection, it can be painted to prevent rust never paint the actual strap though.
Always use the shortest straps possible

Always keep all your grounds clean, that mount looks a little crusty how are the connections between the mount and tub, how about the stud and mount, good and clean?
 

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That appears to be a Firestik Firering mount. Is that what you're running? Is the insulated shoulder washer in place under the spring, between it and the mount? I can't tell if it is or not.

That white object, the insulated shoulder washer, positioned immediately above the "mounting surface" as shown below absolutely must be there. If it's not, your antenna is shorted to ground which will produce that high SWR you're having trouble with.

 

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Something else that could cause high SWR's that Jerry or myself haven't touched on is making sure the cable connection are tight at the radio and antenna stud. Just snug them up good, no need to get over aggressively tight.

That happens from time to time on mine in the Jeep. The PL259 connector at the radio end will come a bit loose from vibration after a few offroad excursions. On my radio though I get a "Antenna Waring" display on the LCD screen. Some radios will have a small red light that will illuminate when the SWR's are too high.
 

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Discussion Starter · #11 ·
I seem to be missing the insulated shoulder washer. My guess is when we were putting the tub back onto the frame, and everything else ... it vanished.

Now, where can I get one of those? If I recall ... and this is a 16 year stretch recall ... I think the nylon washer had a flange ... which goes with what you're saying about isolation.

Thanks in advance!
Doc
 

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Discussion Starter · #15 ·
Well .... I got the nylon wash replaced ... but still SWR goes off the charts!!! Ugh.

Next, I'm going to check the mount (see my image above) for continuity, but after that, there are two options left ... the next would be to replace the cable ... then the radio itself ....

Any other suggestions?

The cable should be 18', iirc, yes?

Doc
 

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. . . the cable should be 18', iirc, yes?
There is nothing magic about 18' of coax for a CB installation. It is Internet myth. One should use the shortest length between antenna and radio without kinking or sharp bends.

See this webpage: Exposing the 18' CB Coax Myth

The reason for using an 18' length of coax cable with pre-assembled connectors is convenience. Most people don't know how or don't want to solder their own connectors. For a Jeep with a tail light or rear bumper/tire carrier antenna mount the 9' pre-assembled coax is too short and the typical 18' length is too long. Just take the excess and either snake it around under the carpet or put it in a zip-tied skein (figure 8), not a coil which will create a RF choke.

The antenna is the most important part of your CB system. You have a new mount and new antenna. Coax doesn't last forever and new coax in a pre-assembled 18' length is only about $20-25. I recommend that you use all new components for your antenna subsystem and not waste time and energy chasing ghosts.

Best of luck.

---------------------

P.S. - The antenna mounting plate in your photo looks suspect. Your antenna mount needs to be well grounded to the mounting plate and the mounting plate needs to be well grounded to the body of your jeep. The corrosion visible in the photo suggests that a bad RF ground may be a significant part of your problem.

Also, why is your antenna at a weird angle? If the stud mount is assembled correctly your antenna should be perpendicular to the horizontal surface of the mounting plate.
 

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Discussion Starter · #17 ·
Mr. Bills, thanks for the link to Stu Olsen's page! Stu has helped me many times over the past 17 years ... and I do now remember that article. I agree, but I'm also of the opinion that I'll just grab the 18' and make my life easier, since it is all assembled, and I'm not going to notice the 0.02349% difference. LOL

I think I do have to chase ghosts though, because I may not have a proper ground anymore. I had to swap out my frame, so it is very possible I may need to put a number of ground straps on some key places, as mentioned above.

However, if someone can humor me ... if the nylon washer isolates that antenna from the mount, why does it mater if the mount is grounded ... or not? Is it not isolated?

With respect to the image and antenna above, I'm not sure why it "looks" like it is at an angle. I can assure you it is perpendicular.
 

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. . . if someone can humor me ... if the nylon washer isolates the antenna from the mount, why does it mater if the mount is grounded ... or not? Is it not isolated. . . ?
The antenna mount must be grounded to create the counterpoise for the antenna, i.e. the all important ground plane.
 

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However, if someone can humor me ... if the nylon washer isolates that antenna from the mount, why does it mater if the mount is grounded ... or not? Is it not isolated?
Consider a classic dipole antenna that most people born before the 90s are all too familiar with; the rabbit ears.


Each side of the antenna is isolated from the other until we reach the transmitter/receiver or transceiver.

So why don't we see antennas like that on our Jeeps? Because they're big and unweildy at the frequencies that CB operates on. A full wave antenna would be 36 feet long. Fortunately we can cheat a little and we can use multiples of the wavelength along with loaded coils to cut our antenna sizes down a bit.

But what do we do with the other half of the "rabbit ears" that we never see? That's another way we cheat on the sizes of our antennas; we use the body of the vehicle as the other half of the radiating element. But we still have to electrically isolate the two "halves" of the antennas from each other. That's why the nylon washer exists.

So the actual antenna is one part, but what happens underneath the nylon washer is just as important. That's why it's vital to have good metal to metal contact between the mount and the tub of your vehicle so you can get as good of a pattern as possible and get as much of that energy out and away from your transmitter.
 

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Discussion Starter · #20 ·
I don't know why I hate electricity, but sometimes I do.

I'm trying to check to see if the antenna mount is properly grounded with this damn DMM. How do I do it? Is it set to 20 Ohms ... then one lead on (-) terminal, and other probe touches the mount? If result is low resistance ... then the mount is grounded?

The reason I ask is because I followed some terminals screwed into the tub under the hood. Did the same procedure to check the grounds under the hood ... and found the terminal lug (where screwed to the hood) was <1 Ohm ... but not the screw or tub ... they showed open circuit.

Your patient and kindly explanation would be greatly appreciated. Thanks in advance!
 
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