My power meter has a direct input to an AD8307 Log Amp module. This gives a range of -80 to +20dBm sensitivity, with reliable measurements from -70 to +10dBm.
To use it at higher powers attenuators can be used. These can be made with an high wattage input resistor of 50R, to act as the dummy load, a series resistor into the 50R input impedance of the AD8307 module in a resistor divider. The maximum input to the AD8307 is +10dBm or 10mW for linearity (it can tolerate 20dBm, 100mW).
The aim is for 10W in to give a reading of 10mW on the meter, this needs a series resistor of 2200+100R. I have checked the readings by comparison with the power output indication of my ELAD FDM-DUO SDR.
This is the screen layout, the small signal showing is from a short antenna connected to the input picking up local RF noise... The bar has a range of 100dB
The new Arduino code for the power meter called SIMPLE_WATT is here.
LOOP TUNING
A new use for the now sensitive power meter is to tune my AL-705 loop. I connect a short antenna to the power meter and place the unit close to the loop. On transmit (either by my FDM-DUO 5-8W, or my new U3S WSPR TX 250-200mW) it deflects and allows me to tune the loop using my new remote motorised capacitor controller (see below)
Great stuff.
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