I have a Daiwa CS-201A two position switch. The single side is connected to by quarter wave vertical (40m). The A and B sides are connected to an IC-7300 and TS-830S.
The switch is claimed to have 60dB of isolation. It also shorts the unused port to ground.
If I transmit 100W (50dBm) from the TS-830S to the antenna, am I correct in that about -10dBm will leak to the other side into the IC-7300?
I tried it and saw about +40 over S9 on the 7300. The service manual for the 7300 says never give it a signal over 20dBm (0.1W).
Am I safe doing this? How can I tell if it’s too much?
UPDATE: I did some testing with an Elecraft XG3 signal source. It produces signals at -107dBm (1uV), -73dBm (S9), -33dBm (S9+40), and 0dBm.
Following the instructions using the 1uV signal and a DMM on the speaker output, the MDS is around -135dBm and -142dBm with the preamp off and set to 1, respectively.
Also, the -73dBm signal is showing just shy of S9 on the S meter. That worried me a little, but I saw in the August 2016 QST magazine article that the ARRL test showed an S9 with a 70uV signal. So there's an error of about 3dB (which is also the S unit increment on this rig's meter).
So I think my receiver is still okay.
I also tested the isolation of the switch by hooking the 7300 to port A, the signal generator to port B, and a dummy load to the common port. With switch in the B position (allowing a direct path from the signal generator to the dummy load), I set the signal output to 0dBm and noted the S meter deflection on the 7300. It was around S5.
I don't know exactly what signal level that is, but it's less that what it read when I fed -73dBm directly into it. So even if we overestimate the received signal at -73dBm, that's still at least 73dB of isolation- if I'm thinking this through correctly. This was done on at a frequency of 7.020MHz. I think the switch claims an isolation of 60dB at 600MHz. It appears the isolation improves as you go down in frequency.
Added a bounty for feedback on the tests and the data. Is it really possible for the switch to have that good of isolation? Is there anything else I should look into? Do the tests seem valid? Am I in the clear running two rigs on this switch?