[TenTec] receiver isolation

Kim Elmore cw_de_n5op at sbcglobal.net
Sun Dec 10 13:37:15 EST 2017

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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