Good report Dave,The requirements and good practice for weak signal reception work are an interesting subject. I made a small investigation a while back of the use of isolating transformers for tackling LF noise. A transformer at the antenna, and another at the receiver both reduced the amount of QRM which I presume was otherwise conducted from the house and added to the antenna's signals at the feed point. This practice isolated the coax braid at both transformer locations. Both transformers were wound onto junkbox toroids, so there was little scientific or technical approach in selecting materials or sizes. Notwithstanding, reception at 136 kHz was improved sufficiently to enable reception of WSPR transmissions.
I could/should improve the antenna grounding point, which was hastily improvised from an iron stake that was to hand. Not ideal in terms of size or material! The long wire needs to be restored after the winter storms here in California, so this would be a good opportunity to improve the whole installation.
Ed
We are much less at risk of lightning storms here in our part of Ca,