The E field antenna could be very small, just need a higher gain amp on it…
I too have often wondered what exactly is in that antenna, out of interest I looked at the signals on the connecting cable… at that stage they are still reasonably wideband analog, ie there was a fair bit of am radio along with the noise… certainly a lot of gain up top, I would guess maybe some sort of log amp to deal with the huge dynamic range of signals… as well as some pre-filtering…