| This is where it all starts, the modulator.
This rack creates a frequency shift signal (FSK), with a 25 Hz shift at
a 50 baud rate. The narrow shift, and low data rate are required due to
the bandwidth limitation of the antenna system. Like any short antenna,
the Q is very high and the bandwidth is narrow. The operating frequency
for NSS was 21.4 kHz. The wavelength at this frequency is about 8 miles!
So, even with the huge towers, and miles of wire (shown later) the antenna
is still short. The low frequency was used to communicate with submarines
at depths fo up to 65 feet.|