H field big difference in gain

[DrRobin]

Hi,

I made a scope probe for my iPad and took some spectrum plots last night of the noise at my location.

   

Norvik - 16.4kHz -67dB (13dB over the noise);
Rosnay - 18.3kHz -56dB (24dB over the noise);
Anthorn - 19.6kHz -49dB (31dB over the noise);
Skelton - 22.1kHz -65dB (31dB over the noise).
(Note the frequency response tails off on an iPad over 20kHz, even though it was sampled at 48kbits/sec.

I have order LTC filter chips to try to reduce this.  If I look on the scope view 19.6 & 22.1kHz dominates the background noise, so might try filtering over 18kHz first.

Robin