Steps to compare GNSS antennas.

Basing this off the idea of comparing SNR proposed by Tallysman GNSS

Steps:

1. Log NMEA strings including G.GSV and G.RMC
2. Use the RMC times to make the start and stop the same for each file
3. Use wolfgangr/perl-nmea to plot the SNR for different satellites and log statistical data about them.
4. Higher is better.

   To give some idea of values to be expected, 54dB is amazing, 53dB is excellent, 52dB is good and 49/50dB is “ho-hum”.

   I didn't see anything above 46, but it's probably fine.

It also outputs some plots of SNR for a visual representation of the statistics.