Radio Propagation Basics
Radio propagation on the primary frequency is usually good out to three thousand miles or more from the MARSRADIO station. Between 3,000 and 6,000 miles, propagation is less reliable but is often acceptable. Nighttime propagation (US time) on the primary frequency is less reliable than daytime propagation, particularly during or around the winter months.
Stations operating at night monitor both the primary and alternate frequency in order to compensate for the possibility of poor nighttime propagation on the Primary Frequency. It should be noted that many nights the Primary Frequency works just fine.
Attempts to contact MARS should always start with several calls on the primary frequency. If there is no answer on the Primary frequency, the alternate frequency should be tried. When able, include your location on the initial call. MARS stations use directional antennas that need to be pointed in your direction for best reception.
Radio Propagation on the primary frequency is able to cover long distances because it is reflected off the ionosphere and back to the ground. Depending on the distance, it may be reflected back and forth between the ground and ionosphere several times. This type of radio propagation is commonly referred to as skip. Skip propagation results in an area of poor reception when you are between 200-500 miles from the MARSRADIO station because the radio waves have gone overhead, and are reflected back towards earth hundreds of miles further out. MARSRADIO compensates for the areas of poor propagation by having several stations in different locations around the US in operation at the same time.
The primary frequency is the best overall frequency for long distance communication. During the winter months, the ionosphere tends to be less reflective at night, and this results in the radio waves continuing straight off into space. During these nighttime periods, the net monitors the Secondary Frequency as well as the primary frequency.
Radio propagation on the alternate frequency tends to follow the curvature of the earth via ground wave. During daylight hours, this frequency is reliable to 1000 miles or so. At night, the range improves to 3000 miles or more. You will notice the same effect when listing to AM Broadcast radio. At night, you are able to hear AM Radio stations from around the country, while during the day only stations in nearby cities can be heard.
While MARSRADIO has two frequencies that it monitors, it also has eight other frequencies that are available for use when propagation favors a different frequency, or traffic levels require.