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Re: [TenTec] receiver isolation

To: tentec@contesting.com
Subject: Re: [TenTec] receiver isolation
From: Kim Elmore <cw_de_n5op@sbcglobal.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 10 Dec 2017 12:37:15 -0600
List-post: <mailto:tentec@contesting.com>
I may need to implement something along the lines of what's been described in here for receiver isolation. While my DXEngineering Receiver Guard will protect the RX ANT port from monstrous RF inputs, when my K9AY loops are set to the direction of my TX antenna, I still get enough RF into the RX ant port to disrupt my Orion II when running 1500 W. If I crank in 6 dB of RX attenuation, the problem is alleviated so I must be right on the ragged edge of "too much RF at the RX ANT port." I have a CMC on the RX feedline. If the loops are set to any other direction, the problem vanishes, so it's not getting in via common mode nor is it getting in via the control line. Since this is on the low bands only (80 m and 160 m) I barely notice 6 dB of RX attenuation, anyway, so that's the fix for now.

Kim N5OP

On 12/7/2017 8:34 PM, Dukes HiFi wrote:

I have been repairing an Icon IC-756 Pro 2. It is AMAZING what they went 
through to keep transmitted RF out of the receiver input.

They actually pick u[p on the TX 5 volt line and drive a transistor, which 
pulls a pair of series PIN diodes directly to ground (through a 0.1 uF 
capacitor). When this affair shorted out, the attenuation was over 90 dB!

It would be easy enough to do this for any radio with a separate receiver 
antenna input. The circuit only has about 8 parts.


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