Hi PrcGuy,
wfview derives signal strength from a single number that the radio provides. If you've read much about the 7300, you know that the S-units are scaled differently from most radios. I have thought of "fixing" the scale to make it more standard. Perhaps that will be an option in wfview one day.
For now though, if you really want to measure antenna gain, I have done this using another technique that is more suited for recording measurements. My son and I wrote some python code to take periodic readings from an RTL-SDR, plus a GPS snapshot (time and position), and write these data to a CSV spreadsheet. The entire thing can be run in the car using a Raspberry Pi or a laptop. I did this and drove around town maping out my repeater coverage, it worked very well. The CSV file was actually quite easy to overlay into google maps as a sort of 'heat map'. Probably the most challenging thing about this was figuring out how to derive signal strength from a spectrum. I ended up using power spectral density, an integral of all the spectra over a bandwidth. The CSV file has the complete spectrum as well as the measured signal strength in dB. You have to be careful to set the gain of the RTL-SDR (and keep it at one setting) for the test, generally setting the gain at the strongest spot (ie, the transmitter site) before driving out.
Here's the code if you are interested:
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