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Re: Topband: 4sq receive antenna side filters?

To: Grant Saviers <>,
Subject: Re: Topband: 4sq receive antenna side filters?
From: "Richard (Rick) Karlquist" <>
Date: Mon, 11 Sep 2017 11:06:34 -0700
List-post: <>
The Achilles heal of active whip receive antennas is the
inability to do filtering ahead of the amplifier.
I have spent many hours
brainstorming this problem, and have yet to devise a
solution.  Especially one with 40 dB rejection.
I am thinking that if there was any way to
do this, DXE would be selling it as an option.
If anyone reading this has a solution, I would love
to hear about it.

As an alternative, see this URL for a passive receive
4 square design:

There are no amplifiers to overload.  You can put a
rejection filter at the receiver.

Rick N6RK

On 9/11/2017 7:25 AM, Grant Saviers wrote:
I was asked by a DXpedition leader if it was practical to bandpass filter the input (antenna side) of the DX Engineering 4 sq's they plan

A deeper question is what impedances are possible for a 20' whip and the input of the amplifier for a filter design?  Sacrificing noise performance, some gain, and frequency range are all reasonable to solve the problem.  Probably more than 40db of rejection is needed. Switching a pair of filters with an outboard box on each whip looks to be the easy part.

Grant KZ1W
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