A AD8307 power meter based on K9IVB design is builded. A single opamp with a gain of 4 provides 4*25 mV/dB = 100 mV/dB. So it can drive a simple +-20V meter with direct dB readout. So the -6.88 V is really -68.8 dBm. The voltage range is +2V down to -7V for +20dBm to -70 dBm. The R4 has to be adjusted to 2.66V. R1 = 10Kohm, R2 = 30 Kohm (2*15 Kohm in series or 12+18 Kohm), R3 = 470 ohm, R4 = 500 trimmer 10 turns, C1,C2 = 22uF /16V. The switch is an ON/OFF/ON one and the second ON is selecting the 18650 voltage to display in voltmeter. The 18650 is connected to an eBay 18650 charger with protection. In addition a eBay +-12V power supply from 18650 is powering the AD8307 and the OpAmp.