GMRS Frequencies are in and around the 462 MHz to 467 MHz range. This range is considered “UHF”. UHF is primarily a ‘line-of-sight‘ set of frequencies. However, under specific conditions, such as tropospheric ducting, contacts over ranges of 1500 to 3000 kilometers can occur.

Antenna Height is KING in UHF. Get your antenna as high as you can for the best performance. Power output comes 2nd to antenna height. Once you have true line-of-sight between any two given points, power levels makes little additional difference. The higher you go in frequency, the more true this becomes.

Regarding “tropospheric ducting”… the time of day, time/season of the year and what the weather is doing will play into this characteristic.

Atmospheric conditions are also impacted by the solar cycle.

Propagation is truly an endless science. You can get reflections, knife-edge propagation (aka diffraction), localized ducting…. Any number of things can occur…which can make it better or worse! Even the type of foliage can aid or hinder propagation. For example, being surrounded by lines of pine trees will affect UHF differently than, say a line of oak trees.

It must be mentioned that UHF signals actually travel comfortably beyond the visual line of sight, by +/- 15%! This is due to refraction and scatter affects in the atmosphere. The looser, electrically charged ion particles in the air, the more scatter and refraction you get. This translates to better signal quality at distance, and often a small bump in range.

While these principles have more and more of an impact as you go lower in frequency, the lower the takeoff angle and the more the solar weather is spicing things up, the more likely you are to have a significant amount of your UHF signal refracted and/or scattered back to the earth beyond the horizon!

It is easy to want to blame your radios and antennas when things seem subpar, but if you know in fact your setup is working 110%, its likely the ‘overall conditions’.

Check out the Line-of-Sight Calculator
https://www.everythingrf.com/rf-calculators/line-of-sight-calculator
It calculates how far the horizon is from an antenna placed at a particular height. The calculators also calculates the radio horizon. It assumes there is nothing between the radio signals and the antenna horizon.

Learn More About Line-of-Sight Propagation!
https://en.wikipedia.org/wiki/Line-of-sight_propagation

73 & Have Fun! Josh WRKV324 / W4ZZK