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CB Radio Forum - Discussions regarding Citizens Band Radio (CB)

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  #21 (permalink)  
Old 06-18-2017, 5:28 PM
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Quote:
Originally Posted by RFI-EMI-GUY View Post
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.
Grounding the radio chassis won't do anything to solve common-mode RF in the coax. That has to be fixed at the antenna end.
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Old 06-18-2017, 7:07 PM
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Grounding the radio chassis won't do anything to solve common-mode RF in the coax. That has to be fixed at the antenna end.

Unless it is following the power leads into the radio chassis. If you will read my post, I suggested he ground the radio and the antenna.His radio is acting "wonky" which suggests RF current is getting into the chassis.

If this were his own personal vehicle, I would advise him to ditch the mag mount and go with an NMO, As it is he has both an insufficient ground plane, and ungrounded (RF) radio.
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Old 06-18-2017, 9:03 PM
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Grounding the chassis will only help if there is a high-resistance DC power connection. Providing an RF ground at the radio chassis won't fix common-mode RF coming from a crappy antenna. Best case is that it spreads the stray RF propagation to the metal around the radio, which may dilute it some.

The best solution is to prevent common-mode RF from propagating down the coax in the first place, in which case it won't matter if the radio chassis has an RF ground, because it won't have RF potential relative to the vehicle body in the first place. You're recommending putting a band-aid on a sucking chest wound.
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Old 06-18-2017, 9:17 PM
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I think you mean "high RF impedence" DC power connection, which is likely if he is powering this magnet mounted antenna, velcro mounted, no holes allowed CB radio from the cigar lighter socket.

He has two choices, a proper install, or band aids. Apparently his employer won't permit the former.

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Old 06-19-2017, 8:38 AM
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I honestly wish that they had purchased these new trucks with CB hookups but it is what it is. So I did a little bit more investigation. When I have the engine off I don't get the alert period but when I have the engine running that's when I have the alert. Does that narrow anything down? I do use a cigarette lighter port FYI

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Old 06-19-2017, 8:46 AM
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Originally Posted by davidjacobs2012 View Post
I honestly wish that they had purchased these new trucks with CB hookups but it is what it is. So I did a little bit more investigation. When I have the engine off I don't get the alert period but when I have the engine running that's when I have the alert. Does that narrow anything down? I do use a cigarette lighter port FYI

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It only means that the alternator is producing higher voltage than the battery. As a result, more power from the radio , more stray or reflected energy messing with the VSWR sensor. Try grounding the radio and antenna and report back.

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Old 06-19-2017, 9:16 AM
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So could you explain exactly how I ground the radio? In plain man terms? I've been using a CB for about 6 or 7 years both in a personal vehicle and a work vehicle but I've never had this issue before. I just need to know exactly which screw to mount a small wire two and then I'll also have to figure out what bolt I can use in the truck

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Old 06-19-2017, 12:08 PM
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Use one of the screws that attaches the cover to the chassis making sure there is bare metal. It helps to use ring lugs crimped to the wire to make the connection. Grounding the mag mount will require clamping a wire to some bare metal on the coaxial attachment.

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Old 06-19-2017, 12:14 PM
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back years ago i used a big alligator clip on a wire to a screw that held the cover on and just looked under dash for a bare metal that was a good ground spot and clipped it on there,,,, you said it needed to be not permanent,,,,
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