# Q-MAC HF Modem

The **Q-MAC HFHigh Frequency (3-30 MHz) Modem** is a military modem developed by Q-MAC (acquired by Barrett Communications). It uses OFDMOrthogonal Frequency-Division Multiplexing with a BPSKBinary Phase-Shift Keying (1 bit per symbol) sync channel in a gap of the signal. This mode is used in Q-MAC modems and transceivers and supports the transmission of encrypted data and digital voice.

## Characteristics[edit]

This Q-MAC mode uses DQPSKDifferential Quadrature Phase-Shift Keying (pi/4 QPSKQuadrature Phase-Shift Keying (2 bits per symbol)) in the data subcarriers. On the lower frequency side there are 20 of these subcarriers running at ~43.1 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. each. Each subcarrier is spaced ~54.1 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). from each other.

About ~200 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). above the 20 subcarriers is a synchronizing BPSKBinary Phase-Shift Keying (1 bit per symbol) channel repeating the same pattern over and over again. This BPSKBinary Phase-Shift Keying (1 bit per symbol) channel also runs at 43.1 BdBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second.. About ~190 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). above the synch BPSKBinary Phase-Shift Keying (1 bit per symbol) are 10 DQPSKDifferential Quadrature Phase-Shift Keying subcarriers all with the same parameters as the previous group of subcarriers, giving the total number of data subcarriers to be 30, plus the one sync BPSKBinary Phase-Shift Keying (1 bit per symbol) channel, 31.

The raw data rate is ~2586 bpsBits per second (bps) with all the 30 data channels.

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