As has been noted there is a lot of noise in ground connected systems. I would suggest using an E-field probe. There are various designs around but its very small and consists of a 15 x 15cm copper PCB panel connected to the gate of a high impedance FET amplifier. This is followed by a simple emitter follower that produces a low impedance output into a regular laptop sound card. No tuning requires as this is a totally broad band E-Field amplifier. I use the SAQ Panoramic Receiver software which has excelent digital filtering to 50Hz and covers from DC to about 22Khz. There are versions that can cover higher if your sound card can handle fast sample rates.
I hope this helps and I was getting very good copy last summer and all ready and waiting for this one on Sunday.
73s G4BIP
