One of the problems, I think, is Relay 0 and the jumpers are not shown in the U3S instruction manual's schematic. The switched relay board's schematic only shows the 5 relays that it controls. But, the block diagram of the switched relay kit and the circuit description are helpful understanding the action of Relay 0. Why, because I believe Relay 0's wiring and operation are identical to the five on the relay board.
(Paraphrasing the Theory of Operations here) For any un-energized (not in use) relay both input and output of the associated LPF are shorted to ground. When a relay is energized (used) then the LPF is connected between the "RF Input" bus and the common LPF output bus. In use only one relay should be energized at a time.
The W0-W1 and W2-W3 jumpers put LPF-0 into the common LPF output bus. Another way of saying this is the jumpers 'energize' and activate the LPF-0 position all the time. This you don't want when adding the switched relay board even if there's not LPF module installed there.
I believe if you want to move forward and use a populated switched relay board with the U3S without having Relay 0 installed you need to cut those jumpers. Naturally, you won't be able to use LPF-0's position. You will also need to connect your antenna to the switched relay board.?
Good luck and I hope this helps!
--Al
WD4AH
