The results for the linearity test are detailed below. The test circuit did not have any frequency compensation components
installed in the front end. It has been stated in articles that these components are not required for HF frequencies. However I believe there is enough variation in the results to warrant some
work on the front end circuitry in order to further decrease the variation
between the different readings at the various frequencies. I believe the adc in the ATMEGA 328 can detect some of those variations. In the case of the -70dBm level the difference between the min and max readings for only the HF frequencies is 63mv.
While the end result after processing by the adc in the
ATMEGA 328 may result in only a portion of a dBm, I think it’s important to get the
best results you can in the hardware first. Then this should result in
minimal compensation or "fudge factor" in the software. i.e. calibration factors.
Next up will be connecting the circuit to an Arduino and re-run the tests and see how the 8307 behaves when connected to the processor. Should be interesting. Experiments done a few years ago I was able to get an accuracy of within 1 dBm and better in most cases. Another thing that will be interesting will be comparing the behavior of the 8307 with signals not as clean as the sine wave I'm using now.
73, Peter
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