2015-09-03, 10:53
As a further thought, do high powered VLF transmissions affect this system in any deleterious fashion? NPL's 60kHz MSF is a keyed carrier wave transmission but the rise/fall times are quite slow. Skelton's VLF transmissions at around 20kHz are probably some sort of FSK (I really should take a listen). In both cases I expect the biggest problem would be amplifier blocking due to high signal strength rather than any sort of pulse detection anomalies.
I'm mindful of the need to avoid any circuitry in the antenna system that might affect timing, such as resonances within the VLF spectrum. This makes it difficult to reject unwanted signals - effectively the system is a baseband receiver with a few 10s of kHz bandwidth. Perhaps notch filters could be added, since these are in effect anti-resonances, but I don't know what unwanted side effects they might have. Fabricating something with sufficiently high Q would also be an interesting engineering challenge!
I'm mindful of the need to avoid any circuitry in the antenna system that might affect timing, such as resonances within the VLF spectrum. This makes it difficult to reject unwanted signals - effectively the system is a baseband receiver with a few 10s of kHz bandwidth. Perhaps notch filters could be added, since these are in effect anti-resonances, but I don't know what unwanted side effects they might have. Fabricating something with sufficiently high Q would also be an interesting engineering challenge!