This meter used an AD8307 module to measure RF powers from -70 to +20dBm (micro-watts up to 100mW), and displays these on an OLED display, as a top bar (limited to -20 to +20dBm, 0.01 to 100mW), the RMS voltage, the actual dBm value and the power (watts) into 50R. Details of this are down this blog (see September 2018). Arduino Nano software is here. There is a direct input RF _METER also another version RF_METER_30 of the software which shows the actual dBm and Power when using the -30dB TAP.
Note, the AD8307 needs a 12V supply, and has the module from SV1AFN has a native input impedance of 50R.
HIGHER POWERS UP TO 100W
For higher power measurements (e.g. +10dBm to +50dBm or 10mW to 100W) a "TAP" or resistive divider can be used. I have now made myself up a very small box containing a 50R/50W RF dummy load and a -30dB TAP (x1000). The dummy load is switched so that I can use the box alternatively as an RF voltmeter (with 760R input impedance) or with a switched-in TX dummy load.
This works very well for powers up to 100W (but needs a better heat sink at this power!). The RF METER effectively displays +10 to +50dBm (10mW to 100W) on its bar scale and related values for voltage, dBm and power.
This is a dBm/power table that maybe useful:
VNA
Sticking this on the Nano VNA I get these numbers
Marker at 30MHz
This shows the 50R load is not usable across the V/UHF range, but usable on HF up to 30MHz or so with a reasonable SWR.
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