Power off the unit. Press and hold the PTT button on the mic and the FM button (second from left) simultaneously while turning the power knob back on. Hold for 5 seconds until the display restarts.
Specifications (typical)
The QYT KT7900D is popular for its "wide receive" (RX), but transmit is usually limited to amateur bands. The service manual reveals the PLL control logic and the band-pass filter switching diodes. Advanced users use this information to carefully enable TX outside the standard bands (for legal MARS/CAP use only—always follow your country’s regulations). qyt kt7900d service manual
Ensuring the device remains within FCC Part 15B or other regulatory limits for spurious emissions. Power off the unit