Hi Alex. I have long been fascinated by whistlers (genetated by lightning or sprites). I ave never built a ereceiver for it but I am very experienced in receiver design so I would like to ask what frequency range (in kHz) would you like it to receive? ULF is a bit broad in terminology. I think that ULF may well be audio as VLF already goes down to 20 kHz. Any lower and you can hear it as audio. Alittle more information will be good.
