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).
Appendix — useful test points (examples) qyt kt7900d service manual
If you accidentally transmit without an antenna (high SWR), the PA chip or the RD15HVF1 transistor can fail. The service manual provides the schematic so you can trace the RF path, measure voltages at the bias pins, and source correct replacement components. The QYT KT7900D is popular for its "wide
Do not expose the unit to prolonged direct sunlight (e.g., on a vehicle dashboard). Programming & Software measure voltages at the bias pins