What is a center frequency?
The psk modes use a carrier which is phase modulated. This signal is generated in the audio domain. Through a clever modulation scheme the modulated signal is quite narrow. In fact, a PSK125 has 2 sidebands of 62.5 Hz on either side of the carrier. The carrier is the center frequency, and as the sidebands are perfectly symmetrical you find the center frequency right in the center of the signal. PSKmail uses Fldigi to generate the audio signal. To shift it into the HF domain we give it to an SSB transmitter . In USB mode the center frequency = VFOfrequency + Audiofrequency. In LSB mode the center frequency = VFOfrequency – Audiofrequency. Example 1: If you generate the audio signal at a frequency of 1000 Hz and the TRX VFO is at 10147 kHz, the center frequency is 10148 in USB mode and 10146 in LSB mode. Example 2: You want to use USB mode to work PI4TUE on 10148 and you use Fldigi to generarte a psk signal at 1500 Hz. You have to tune the rig to 10146.5 kHz.
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