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.
Gary
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