rickman wrote in :

The US located beacon added PSK a few years
back to make the signal easier to receive.

I went Googlong after I wrote that last one. I'd have thought PSK would be
harder to detect than AM. So much for what I know. I read that
wris****ches can detect the PSK signal too, so low power must have been done,
with a small antenna too, but I don't knpow what they did so I'll leave it
there.

About op-amps, I just found it hard to let go of a favourite idea. Too
many transistors though...

Just one thought left that might be a kernel of a new idea: if you have a
tiny resonant circuit at 60KHz, with high Q, then the change of phase ought
to make some kind of detectable upset, a spike maybe, whose polarity you can
use to determine mark or space in the signal. The combination of resonance
and short spike duration might give you a usable combination of low power and
detectable threshold.

I'll stop there because I don't think I have anything you can use.. I'm
interested in what you come up with though, especially if it avoids a large
antenna.