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Re: [TowerTalk] Are All Low-Pass Filters Alike?

To: "Wayne Greaves" <>,<>
Subject: Re: [TowerTalk] Are All Low-Pass Filters Alike?
From: Jim Lux <>
Date: Tue, 16 Aug 2005 08:09:26 -0700
List-post: <>
At 06:14 AM 8/16/2005, Wayne Greaves wrote:
>Several LP filters are reviewed in the August 2002 QST (but not Ameco).
>Response curves, insertion loss, and other specs were measured in the ARRL
>lab and compared to manufacturer published specs.
>Wayne, WØZW

But were they measured into a mismatch?

Apparently not, based on a quick reading of the review.  They measured the 
input looking into the filter from the transmitter, but presumably they 
were terminated into 50 ohms.

This is a real problem when you're trying to do harmonic suppression.  More 
than one designer has been bitten by a filter that attenuates well close to 
the passband, but doesn't have very good attenuation farther out.

I'm not saying that the filters in the review don't work, nor that you 
can't design a filter that works into any load impedance, but, as someone 
pointed out, without any meaningful specs, it's all just advertising.

Jim, W6RMK


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