This mW meter is based on the original idea from W1GHZ who used inexpensive power detector ICs. In this implementation a microcontroller (ATMEGA 168) is used to measure the output voltage from the power detector chip and translate it into dBm. A lookup table is programmed in the micro’s flash memory containing calibration data (provided by SV1FXO) for various bands of interest. This greatly improves the meter’s accuracy and extends the LTC5508’s measuring capabilities up to 10GHz with “ham radio grade” accuracy.
Two remote heads, one containing the LTC5508 and the other the LT5534 can be connected to the main unit via a cable. Inside the enclosure resides the microcontroller (and the rest of the circuit), a character LCD screen and two 400mAh lipo batteries which provide the necessary power.
With this simple and inexpensive homebrew instrument QRPp power levels from VHF to 10GHz can be measured. For higher power an input attenuator can be used (the firmware provides the option to enter the attenuator’s value so you can read directly the power before the attenuator). Other features -averaging, peak hold and relative power measurement- are provided in the firmware which was developed and written by SV1OBT.