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Re: [TowerTalk] Low Pass Filters: Are They Of Any Use Today ?

Subject: Re: [TowerTalk] Low Pass Filters: Are They Of Any Use Today ?
From: Jim Brown <>
Date: Mon, 16 Apr 2012 13:28:41 -0700
List-post: <">>
On 4/16/2012 12:20 PM, Richard Solomon wrote:
> Given that the vast majority of TV's are on Satellite or Cable, is their
> anything to gain by sticking a Low Pass Filter in the Transmission Line ?

Put very simply, NO. And even if a TV is on an outdoor antenna, it's 
hard to find a good reason for an LPF. Since the final shutdown of 
analog TV several years ago, nearly all broadcasters have abandoned TV 
channels 2-6, so 174 MHz is the lowest frequency still in use in 95% of 
North America, and the majority of TV broadcasters are on UHF. The 
reason for abandoning 2-6  was impulse noise, which is stronger on these 
channels and makes a mess of digital signals. There are a few 
exceptions, mostly in less urbanized parts of the Midwest, where there's 
less impulse noise, and where the better propagation of low-band VHF 
signals allows lower transmit power to achieve the desired coverage.

Nowadays, the dominant causes of RFI to consumer products of all sorts 
are some form of inadequacy in the design or construction of the victim 
-- either some form of The Pin One Problem, inadequate shielding of the 
victim, and inadequate bandwidth limiting -- and nothing we can do with 
our transmitters will help any of that.  The best we can do is use 
antenna location and directivity and/or reduce power to minimize the RF 
at the victim.

Jim K9YC

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