Editing Category:Diplomatic (section)

== Digital Modulation Modes in Diplomatic HF ==

Because shortwave channels suffer heavily from fading, multipath interference, and atmospheric noise, diplomatic modems rely on specialized digital modulation techniques. These are designed either for extreme robustness or maximum throughput within a standard 3 kHz single-sideband (SSB) radio channel:

* '''PSK (Phase Shift Keying):''' Shifting the phase of a carrier wave to represent data bits. Standard '''BPSK''' (Binary PSK) changes the phase by 180° and is exceptionally resilient under weak signal conditions, while '''QPSK''' (Quadrature PSK) uses four phases to double data throughput.
* '''MPSK (Multiple Phase Shift Keying):''' Utilizes higher-order phase configurations (such as '''8PSK''') to send multiple bits per symbol, maximizing speed when ionospheric conditions are clear.
* '''MFSK (Multiple Frequency Shift Keying):''' Transmits data by shifting across a pre-defined array of distinct frequencies (tones). Because only one tone is active at a time, it is highly resistant to selective fading and Doppler shift, making it a favorite for automated setup sequences and lower-speed, high-reliability networks.
* '''OFDM (Orthogonal Frequency-Division Multiplexing):''' Instead of a single high-speed tone (serial-tone), OFDM splits the 3 kHz radio channel into dozens of closely spaced, low-speed subcarriers operating simultaneously. This parallel approach natively combats multipath dispersion—where a radio wave bounces off the ionosphere and arrives at the receiver via multiple paths, causing echo and distortion.