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Re: [TenTec] notch filter for Eagle?

To: tentec@contesting.com
Subject: Re: [TenTec] notch filter for Eagle?
From: Jim Brown <k9yc@audiosystemsgroup.com>
Reply-to: k9yc@arrl.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 20 Jul 2017 10:28:35 -0700
List-post: <mailto:tentec@contesting.com>
On 7/20/2017 7:38 AM, Joe Papworth via TenTec wrote:
Those carriers around 14030 may be from a wireless router.

More precisely, they are leakage from wired Ethernet systems. Wired Ethernet uses a free-running clock that is synchronized with the Ethernet Hub or Switch; we typically hear our own system and those of close-in neighbors. When I lived in Chicago with houses spaced about 40 ft, I typically heard 3-5 of them spaced from about 14029.5 to about 14030.5. There are other clusters on 15 and 10M. It's easy to figure out which signal is coming from your system by killing power to the Hub/Router/Switch.

These signals are radiated by the Ethernet cable, and can be suppressed by winding the Ethernet cable through a ferrite core to form a common mode choke, following the guidelines for RG8X-size cable in k9yc.com/RFI-Ham.pdf Virtually all WiFi access points and cable/DSL modems include an Ethernet port, so their wiring also radiates this trash.

Note also that both the computers and the Ethernet Hub/Switch/Router are sources of this noise, so if the wired Ethernet cables are longer than about a tenth of a wavelength, a choke may be required on both ends. Even better, avoid Ethernet by using only WiFi, so the only noise source is that Router/Modem. The cable(s) interconnecting them will be shorter, hence poorer antennas, and they will be the only ones you need to choke.

73, Jim K9YC

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