Experiments with a bit of wet string
I had time the other day, surprisingly, to have a fiddle with the HF active aerial in the loft. This is a Datong AD170 that I've had for decades now. It feeds into a Yaseu FRG7000 and also a Watson SDR dongle.
There is a heck of a lot of noise here and the aerial is far from ideal, being mounted on a purlin in an inverted-vee formation with the ends held on the floor joists, mains and data wiring and the house alarm wiring nearby. So, noise.
But it seemed to fair reasonably well on 40 metres even so. I caught one conversation on the SDR and checked I could receive it on the FRG7000 too which sounded better, probably because the PC has dinky speakers attached. But more to the point I used the Hack Green webSDR and found the same signal. Other signals via Hack Green did not appear here, but fair enough, they won't be using the same bit of wet string and are a way from here. But it was a useful experiment that both my bit of wet string and their setup received the same amateur signal, and neither could hear the other end of the conversation.
Next step, move the AD170 to the apex inside the roof and see if that sorts the noise out. More later.