JIm, thanks for your reply. I have changed menu 31 in the FDM-DUO to 2 antennas, but it doesn't change anything on the DUO-ART screen. I do have the cable connected from the FDM-DUO's EXT-I/O to one of the two corresponding connectors on the ART, but I don't have any USB cables going to a computer, since my first goal was to get the unit working with the amp without a PC. Is that wrong?
I do understand that the preselector feeds the RX connection. I have seen the bypass card, and have made sure that the filter selection says that slot 8 should be used from 10khz to 54mhz, but nothing is making any difference, and I assume it won't until I see the RX+TX indicator showing that receive signal is going to that socket. Whatever I have done, antenna 2 on the FDM DUO sees nothing from the ART.
I have been playing around some more, and now I see that with the FDM-DUO in CoaxRTX (and the antennas setting back to 1), the signal level is the same with the FDMDUO setting or the GENERIC setting, but only below about 2mhz. It rapidly drops off until there's not much left at 80m.
I can't help thinking that I am stupidly overlooking something simple.