[RFI] Low pass filters

Hare, Ed, W1RFI Hare, Ed, W1RFI" <ehare@arrl.org
Mon, 19 Jan 1998 10:48:00 -0500

Almost any low-pass filter will offer at least 30-60 dB of stop-band 
attenuation.  In most cases, IF the intereference is caused by transmitter 
unwanted emissions, this will be quite enough to make the problem go away.

The main purpose of a low-pass xmit filter (or bandpass for VHF 
transmitters) is so that when you DO have an interference problem, you can 
point to it with pride.  :-)  Most cases of consumer interference are caused 
by fundamental overload, not transmitter harmonics.

73 from ARRL HQ,
Ed Hare, W1RFI
ARRL Lab Supervisor
>From: Robert Brandon
>To: rfi
>Subject: [RFI] Low pass filters
>Date: Monday, January 19, 1998 9:27AM
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>>Date: Sun, 18 Jan 1998 14:11:21 -0800
>>From: John Kjos <KB9RPM@centuryinter.net>
>>Subject: [RFI] Filters
>>Any suggestions for Low pas filters for HF.I am setting up a shack and
>>want to have them installed at the start.Thanks John KB9RPM
>Good idea on installing low pass filters right away.  I looked at
>several models and  they all have about the same specs.  I ended up with
>a couple of Drakes and they seem to work fine.  I've had much more
>success, however, working on the other end, that is, adding high pass
>filters and chokes to the TV, stereo, etc.  (Still, it's P.C. to do what
>you can at the xmtr end.)
>One thing to keep in mind with low pass filters is to keep the jumper
>between the transmitter and filter as short as possible -- you don't
>want the jumper to be any kind of antenna for harmonics.  I use a double
>male PL-259 and a right angle adapter to plug it right into the back of
>the rig. Rig a physical support for the filter so as not to torque the
>connections and you're all set.  GL and 73,
>Robert K5PI
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