Generally speaking, a 6dB improvement in the link budget will double the range in a LOS environment (8dBi gain antenna compared to a 21 dBi gain di-pole antenna). To double the range in non-line of sight conditions it takes at least 12 dB of additional receive sensitivity or transmit power.
However, 12 dB of additional antenna gain may not double the range because of the narrower antenna beamwidth which causes the antenna to ignore signals arriving from angles outside of the beamwidth. Improving receive sensitivity is generally the best option to improve range. On some Digi radios, this can be done by decreasing the over-the-air baud rate.
Aug 23, 2017