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Re: Topband: Bandpass filters for receive antennas

To: topband@contesting.com
Subject: Re: Topband: Bandpass filters for receive antennas
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Mon, 31 Aug 2015 09:43:12 -0700
List-post: <topband@contesting.com">mailto:topband@contesting.com>
On Mon,8/31/2015 4:37 AM, Larry via Topband wrote:
I have been following the discussion on front end relays with interest, and I was wondering
what sorts of bandpass filters folks are using for receive antennas.

Bandpass filters do nothing for in-band signals -- their only function is to reject OUT OF BAND signals. The primary reason for using bandpass filters IS for RX. A good 160M bandpass filter would be effective at reducing overload from AM broadcast stations. So would a high pass filter. There is a survey of bandpass filters for contesting at this link. http://k9yc.com/BandpassFilterSurvey.pdf

Most bandpass filters are designed for low power -- 200W or less, and some for only 100W. This means that they must be installed between the rig and the power amp, so they are of no help with killing harmonics generated in the power amp. This is a great application for stubs -- if placed after the power amp, they can significantly reduce the level of harmonics. Here's an applications note that appears in the most recent National Contest Journal. http://k9yc.com/LocatingStubs.pdf

73, Jim K9YC


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