Yes, only a single antenna is being used. I now think something has to
be wrong with the 7030+ because the overload I'm experiencing on it is
actually worse than the overload I experience on my Lowe HF-150--so,
that clinches it. My guess is the SD5400 mixer needs to be replaced,
but that's just a guess. No other aspect of the receiver's functioning
appears compromised. It's as sensitive as ever and an external highpass
filter temporarily improves things.

I can send it off to AOR UK if necessary, though it'll have to wait a
few weeks until my business travel has ended.

If any of you guys have other hypotheses about what the source of this
difficulty is, please let me know. Thanks.

Steve