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Old 06-16-2017, 4:44 PM
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Default "CB Antenna Warning"

So I keep getting the above message every key press on a cobra 29 lx.. I checked the swr but it's really close to 1 on both 1 and 40. What could be the issue. I'm attaching a picture of the antenna and mount. Mount was just purchased from a local CB store. What could be the issue?

https://drive.google.com/file/d/0B4E...w?usp=drivesdk
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Old 06-16-2017, 4:58 PM
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It is rare for an antenna to be perfect or even close to 1:1 on one frequency, let alone at opposite ends of the band. The first thing I would do is make sure the meter is accurate or even try an antenna analyzer.
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Old 06-16-2017, 5:14 PM
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Hook a dummy load to the radio to see if you still get the warning.
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Old 06-16-2017, 7:46 PM
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Sometimes the antenna warning thing in the radio is too sensitive and needs tweaked.

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Old 06-16-2017, 8:01 PM
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I have another radio that's the same model. I'll try to hook it up Monday. If it does the same thing, I'll have to come up with something else

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Old 06-16-2017, 9:13 PM
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One thing that I meant to point out earlier. The mount is an adjustable magnetic mount that is on the bulkhead of a flatbed truck.

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Old 06-16-2017, 10:52 PM
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Quote:
Originally Posted by davidjacobs2012 View Post
One thing that I meant to point out earlier. The mount is an adjustable magnetic mount that is on the bulkhead of a flatbed truck.

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Mag mounts perform poorly at CB frequencies because there isn't sufficient capacitance between the mag mount and the sheet metal. Also, the bulk head of a truck isn't enough of a ground plane. It is likely that whatever RF current would have been meant for the ground plane (counterpoise) is instead traveling on the coaxial cable.
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Old 06-16-2017, 10:55 PM
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Mag mounts perform poorly at CB frequencies because there isn't sufficient capacitance between the mag mount and the sheet metal. Also, the bulk head of a truck isn't enough of a ground plane. It is likely that whatever RF current would have been meant for the ground plane (counterpoise) is instead traveling on the coaxial cable.
You don't think it's enough ground plane? It's got 24 feet of metal behind it haha

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Old 06-16-2017, 10:57 PM
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You don't think it's enough ground plane? It's got 24 feet of metal behind it haha

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If the 24 feet were entirely flat, square and it was placed in the middle perhaps.
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Old 06-16-2017, 11:03 PM
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Quote:
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You don't think it's enough ground plane? It's got 24 feet of metal behind it haha

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The way you have it mounted may be the issue.

With the ground plane going down towards the ground, it's not really a suitable ground plane for a vertical antenna. The ground needs to be relatively horizontal.

While you can make an install like that work, it's going to impact the characteristic impedance of the install.

I wouldn't be surprised if the SWR is high, but this could easily be a number of issues combined:
High SWR due to mount.
Coax damage. Could be pinched however you ran it into the radio.
Could be the antenna is not trimmed correctly.
Could be a bad antenna
Could be a bad mount.
Could be a improperly adjusted SWR warning indicator, as was mentioned above.

Using a reliable SWR meter will tell you a lot. Relying on SWR "warning lights" is not a good indicator of the issue (if there is one).
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Old 06-16-2017, 11:05 PM
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When I bought them out from the TV guy he said that the ground plane will be okay because of all the metal. The SWR read okay (1.2) but I am going to have to get a actual meter and jumper cable to make sure. Like I stated above I will hook up my other radio that's the same exact model and see what is going on.

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Old 06-16-2017, 11:15 PM
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Quote:
Originally Posted by davidjacobs2012 View Post
When I bought them out from the TV guy he said that the ground plane will be okay because of all the metal. The SWR read okay (1.2) but I am going to have to get a actual meter and jumper cable to make sure. Like I stated above I will hook up my other radio that's the same exact model and see what is going on.

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Is the radio unit itself mounted to grounded sheet metal or is the only ground, that which it receives from the power cable? Try grounding the radio to the dashboard mounting bolt with a short jumper and check your readings.
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Old 06-17-2017, 9:17 AM
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I use three magnet-mount antennas ranging from 35 inches to 62 inches. All of them yield excellent results plopped in the center of my vehicles' roof or trunk or, in the case of my Jeep Wrangler used off-road, the hood.

I've seen propagation tests that indicate the magnet mount antenna is an excellent choice for CB users and is highly competitive with any mobile antenna mounted via other methods.

Any SWR problems being experienced is not due to the use of a magnet mount. If one location does not yield excellent SWR results, the magnet mount can be easily moved to a location that does. I've done it many times with many vehicles, and it works very well.
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Old 06-17-2017, 12:59 PM
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Quote:
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Is the radio unit itself mounted to grounded sheet metal or is the only ground, that which it receives from the power cable? Try grounding the radio to the dashboard mounting bolt with a short jumper and check your readings.
The radio is mounted to the dash of the truck by heavy duty Velcro. The company I work for doesn't want any holes drilled so that's my only option.

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Old 06-17-2017, 1:00 PM
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I use three magnet-mount antennas ranging from 35 inches to 62 inches. All of them yield excellent results plopped in the center of my vehicles' roof or trunk or, in the case of my Jeep Wrangler used off-road, the hood.

I've seen propagation tests that indicate the magnet mount antenna is an excellent choice for CB users and is highly competitive with any mobile antenna mounted via other methods.

Any SWR problems being experienced is not due to the use of a magnet mount. If one location does not yield excellent SWR results, the magnet mount can be easily moved to a location that does. I've done it many times with many vehicles, and it works very well.
When I used to run a lil wil antenna, it was awesome. Great results

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Old 06-17-2017, 1:16 PM
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The radio is mounted to the dash of the truck by heavy duty Velcro. The company I work for doesn't want any holes drilled so that's my only option.

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The magnet mount base has relatively high capacitance reactance due to the diameter, thickness of the paint and any rubber or plastic pad between the magnet and the vehicle paint. There will be common mode current flowing on the coax, through your un-grounded radio and its power cable to wherever you are getting negative battery terminal. Some of this current also flows on the positive lead and microphone lead. It is a far from ideal situation. I would run a short jumper from the radio chassis to the vehicle sheet-metal before doing any antenna adjustments. A good external VSWR meter should be used for adjusting the antenna.
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Old 06-17-2017, 1:21 PM
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Quote:
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The magnet mount base has relatively high capacitance reactance due to the diameter, thickness of the paint and any rubber or plastic pad between the magnet and the vehicle paint. There will be common mode current flowing on the coax, through your un-grounded radio and its power cable to wherever you are getting negative battery terminal. Some of this current also flows on the positive lead and microphone lead. It is a far from ideal situation. I would run a short jumper from the radio chassis to the vehicle sheet-metal before doing any antenna adjustments. A good external VSWR meter should be used for adjusting the antenna.
How would you go about grounding the radio? I would like to not have more wires running around.

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Old 06-17-2017, 1:33 PM
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How would you go about grounding the radio? I would like to not have more wires running around.

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I would use a minimum 14 or 16 gauge stranded wire and try to run it to the frame using a mounting bolt attaching some existing hardware near the steering column or pedals. It will be easier if you attach ring lugs to the ends of the wire where they attach to the radio and vehicle body/chassis. Obviously this has to be done safely as not to interfere with the controls or airbag system. You are going to have to look around for that ground point. If it is painted, you will have to sand away paint where the ring lug is screwed down. Make sure the connections are mechanically and electrically tight. You want to be attached to metal that is part of the welded body itself, not some bracket that is a secondary attachment to the body. The shortest connection you can make, 3 foot or less would be the best.

Like wise It might also help to ground the magnetic mount base to the truck bed using a short jumper.

Where are you grounding the black lead now? To the chassis or is it going through the cigar lighter?
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Old 06-17-2017, 1:34 PM
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How would you go about grounding the radio? I would like to not have more wires running around.

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You would need to run a braided ground from the radio (I would use one of the chassis screws or drill my own stud) and find a screw under the dash (make sure it reads to ground). You can use the outer shielding from a piece of coax for a braided ground of you have some laying around.

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Old 06-18-2017, 5:10 PM
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I would guess either you have some RFI issues (RF getting into the radio) likely caused by RF on the outside of the coax( sometimes called common mode current) and/or bad grounding of the radio itself. To ground the radio, I would find a good chassis ground as close to the radio as feasible. Then either use a heavy wire (like 6 guage) or use a run of RG-58 shorted on each end with a .01 microfarad capacitor. My guess is one way or another some of the RF (radiated) is getting back into the radio and the antenna SWR sensor does not 'like' it.

Good luck
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