Moin Stefan,

You wrote:

...
How sensitive is the balanced probe to shielding effects (trees, houses)?

Don't know yet. But see those screenshots. There are much less
local interference lines visible.

Any difference to the E field probe?

This IS an e-field probe, but a balanced one.
Got the idea from there:
http://www.vlf.it/immagine/minimal_E.html
(tnx)

Where do you have the INA111 from?

From Farnell, the TLE2426 voltage splitter too.

What are the differences on 137 kHz? Is there a significant S/N improvement?

Not tested yet. But as I wrote it should work.

Peter, df3lp