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Author Topic: DC Power line Noise Filter CB Ham Radio XLF-20C ?  (Read 5754 times)
CHRISDX
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Posts: 244




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« on: April 01, 2010, 07:41:53 PM »

My friend mentioned this noise filter for his mobile setup. No reviews or posts exist for it.

http://www.copper.com/cart/product_info.php?products_id=1524


Anyone used this or similar?  Myself, I do have alternator whine I'd like to clean up as well.
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K0BG
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Posts: 9878


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« Reply #1 on: April 02, 2010, 02:52:40 PM »

Please notice the information referred to, refers to the noise over the power cable as being common mode. That's not possible.

Brute force filters, which this is one example, do nothing except add resistive losses. They will, in some cases, mask alternator whine. Alternator whine is almost always caused by a ground loop, so using a brute force filter is a poor substitute for fixing the problem.

My take is, if you take your time to install your gear correctly, you won't need any power line filters. You might need a common mode choke on the coax cable, and no doubt need a choke on remotely-controlled HF antenna, but you shouldn't ever have to resort to one of the power cable.

Incidentally, if the filter in question uses a ferrite or powdered-iron core, its effectiveness to quote cure alternator whine is in question too.
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WX7G
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Posts: 6133




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« Reply #2 on: April 02, 2010, 04:52:49 PM »

A quick test to see if a DC line filter will help: Disconnect the transceiver from the car power system. Run it off of its own battery. Start the car. Do you still have the auto system noise? If YES a filter will do nothing. If NO then a filter can help.

Without this test much time and money can be consumed in a fruitless quest for a filter that works (when none will).
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WX7G
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Posts: 6133




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« Reply #3 on: April 02, 2010, 05:19:13 PM »

There can exist common-mode noise on the power cable.

However, a common-mode choke that will be effective is probably not available off-the-shelf. The reason is that the chassis return current takes two paths: via the automobile frame to the radio and via the power cable. Because of this the +12V current thru the common-mode choke is higher than the return current thru the choke. The choke core will saturate, rendering the choke ineffective.

A filter between the radio and the RFI source masks the noise. It can be better to do 'source suppression' by attenuating the noise at the source.
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