Richard Clark wrote:
The ultimate explanation is that if you read the instructions
carefully, you may find they state to try on one wall, or move to
another and try again (pretty much the same advice as that above, less
all the wire and capacitors).

The "synchronization" does not always happen all at once (again, this
is undoubtedly discussed in the instructions - or used to be). You
may spend up to a week discovering the sweet spot where the receiver
responds. We have fielded many such questions as yours in the past,
and I cannot recall anyone coming back after having given up (and I
don't recall one needing an external antenna).

Oh, I'm sure lots of folks ask questions here about these clocks

Believe me, I tried and I was very patient. I tried the clock set up
in five different locations, which included several orthogonal
directions, and I left it in each position for at least 24 hours, and
probably a lot longer. I spent a month on this and I'm not
exaggerating. It was months ago (I *did* give up and my memory is
fuzzy but I know I left it up at least overnight in each position, and
for a week or more in some locations (i.e. on the bench, pointing in
different directions). I never got a sync indoors.

It's just that now I'm trying again, after having given up. Thanks
for your help and I'll try the surrounding-loop solution. Makes me
wish I'd taken that antenna design course in EE school.