You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
The Feb 2025 Radioddity Giveaway Results are In! Click Here to see who won!

Reply to thread

Message

Err that is common mode RFI causing that. Common mode RFI is caused by an inadequate RF ground, not electrical ground, so shifting the negative power wire won't change that. Basically an antenna system needs a source to draw electrons from and return them to. When you have a poor RF ground the source and return is inadequate so the coax, the CB, the microphone and any connected wiring ended up being used as a source and return for electrons and therefore part of the RF ground as the antenna system tries to compensate. The more power you try to put out the worse the symptoms are as your RF ground is even more inadequate for the power you're trying to work with.

I bet if you put on a few clip on Mix31 ferrites on the coax on the outside of the vehicle near the antenna to choke off the common mode RFI you'd see those problems disappear but the bad part is the SWR would go up and this would be confirmation that the coax was forming part of the RF ground which you don't want. When you have a decent RF ground you don't have these problems, using ferrites makes no difference and neither does altering the length of the coax. Unfortunately because RF is AC and multimeters/ohm meters are DC you cannot use a multimeter to test whether you've got a good RF ground, you need an antenna analyser.

<blockquote data-quote="M0GVZ" data-source="post: 578948" data-attributes="member: 22312">Err that is common mode RFI causing that. Common mode RFI is caused by an inadequate RF ground, not electrical ground, so shifting the negative power wire won&#039;t change that. Basically an antenna system needs a source to draw electrons from and return them to. When you have a poor RF ground the source and return is inadequate so the coax, the CB, the microphone and any connected wiring ended up being used as a source and return for electrons and therefore part of the RF ground as the antenna system tries to compensate. The more power you try to put out the worse the symptoms are as your RF ground is even more inadequate for the power you&#039;re trying to work with. I bet if you put on a few clip on Mix31 ferrites on the coax on the outside of the vehicle near the antenna to choke off the common mode RFI you&#039;d see those problems disappear but the bad part is the SWR would go up and this would be confirmation that the coax was forming part of the RF ground which you don&#039;t want. When you have a decent RF ground you don&#039;t have these problems, using ferrites makes no difference and neither does altering the length of the coax. Unfortunately because RF is AC and multimeters/ohm meters are DC you cannot use a multimeter to test whether you&#039;ve got a good RF ground, you need an antenna analyser.</blockquote>

[QUOTE="M0GVZ, post: 578948, member: 22312"] Err that is common mode RFI causing that. Common mode RFI is caused by an inadequate RF ground, not electrical ground, so shifting the negative power wire won't change that. Basically an antenna system needs a source to draw electrons from and return them to. When you have a poor RF ground the source and return is inadequate so the coax, the CB, the microphone and any connected wiring ended up being used as a source and return for electrons and therefore part of the RF ground as the antenna system tries to compensate. The more power you try to put out the worse the symptoms are as your RF ground is even more inadequate for the power you're trying to work with. I bet if you put on a few clip on Mix31 ferrites on the coax on the outside of the vehicle near the antenna to choke off the common mode RFI you'd see those problems disappear but the bad part is the SWR would go up and this would be confirmation that the coax was forming part of the RF ground which you don't want. When you have a decent RF ground you don't have these problems, using ferrites makes no difference and neither does altering the length of the coax. Unfortunately because RF is AC and multimeters/ohm meters are DC you cannot use a multimeter to test whether you've got a good RF ground, you need an antenna analyser. [/QUOTE]

Top Bottom