Oh yes Flip I noticed the Heathkit.Looking on Qrz.com it's amazing the amount of "old gear" people use,especially Americans.Yes Steve ive seen that movie a few times...did you see the transmitter he was using?..It was an old Heathkit DIY model, Prof Opmmur noticed it too lol...In the 1970s i had a Heathkit Mohican receiver 73s mateLol! Yep thanks the time traveling radio ham...reminds me of the brilliant film "frequency"Steve i would imagine the wide bandwidth is necessary for it and i cant even think how we could devise anything at the moment to narrow the bandwidth (selectivity)...let me know if you come up with something...The amplifier would have to be built around its specific fundamental frequency Steve...another thing i leave for you to do lol ::