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| Cheap USB power meters? |
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| Dave_g8:
Hi, For experimentation I purchased one of the low cost ARW227 based RF power meters for around £7 delivered to the UK. The description from the seller. 24-bit ADC USB Type-C power supply -55dBm ~ -5dBm 50dB dynamic range Frequency range : 100MHZ ~ 2.7GHz Input impedance 50Ω The specification seems a little optimistic, since the information for the ARW227 quotes a dynamic range of 45dB for frequencies 0.1GHz to 2.7GHz. The “Main” PCB is connected to the “Display” PCB via a 16-way fixed connector. For curiosity, I separated the two PCB’s, which was a little difficult and I ended up having to repair a few of the tracks. An image of the unit after modifying it to have a male and female connector is shown attached. The basic architecture inferred from the PCB is shown attached. Interestingly there is a separate 24-bit ADC which has a SPI serial interface to the MCU and an AZ431 (2V5) voltage reference. The four buttons select the frequency bands, 100MHz, 700MHz, 1.8GHz and 2.6GHz. I assume there are separate slope and intercept parameters for each of these bands. I am not sure if there is a method to modify the parameters without reprogramming the MCU. Using the limited RF generation sources that I have (NanoVNA and TinySA) and comparing the results with the AD8362, the ARW227 power meter reads about 2~3 dBm higher than expected. As previously pointed out the meter will measure the power over its full bandwidth, so when using the NanoVNA for example, which has a nominal square wave output, the power reading includes the fundamental and the harmonics. 73, Dave |
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