[TowerTalk] Mains Filter for 80M

Jim Lux jimlux at earthlink.net
Fri Jun 8 06:53:38 PDT 2012

On 6/8/12 6:37 AM, Aravind Balasubramanian (VU2ABS) wrote:
> On 6/8/2012 6:20 PM, Wayne Willenberg wrote:
>> I am putting up an 80M dipole at 65 ft and a Beverage antenna for
>> receiving.  In doing my homework for this project, I have been reading
>> ON4UN's book "Low-Band DXing."
>> On page 7-75, the author states "It is essential to feed the equipment at
>> the shack through high-quality mains filters..."
>> Would someone please give me a recommendation for such a "mains filter"?
> http://us.tdk-lambda.com/lp/ftp/other/all_about_emi_epmag.pdf
> Though the below is not a recommendation - it will give you a fair idea.
> http://stores.ebay.com/PLATINUM-TV-PARTS/EMI-FILTERS-MAINS-CONNECTORS-/_i.html?_fsub=918486011
> I get mine from the junk market where these are removed from scrapped
> machinery and have a lot of life remaining in them.
> You can also build your own.
> online electronics part stores like mouser etc will also have the same
> just search for EMI filter

The only potential problem is that you don't know from ON4UN what 
frequencies you want to filter out, and those filters are really more 
designed to keep high frequencies that are inside the box from getting out.

There's also a HUGE variation in performance of EMI filters

Take a look at all the different plots at the bottom of the page..
Some attenuate 50dB at 2MHz.. others only 20 dB.

And, are you concerned about common mode or differential mode noise. 
Filters designed to keep "switching power supply hash" out of the power 
line often have good differential mode attenuation, but not so good 
common mode.

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