PROPAGATION TIDBITS

We have two distinct types of High Frequency bands. Daytime and nighttime.

20 meters is considered to be a daytime band although as the sunspot numbers rise it will stay open later and later.  Higher bands (also considered to be daytime bands) tend to open later in the morning and close earlier in the evening than 20 meters.

The lower bands 40, 80 and 160 are considered to be nighttime long distance bands. 

Usually the 40 meter band is “short” during the day and will go “long” at some point in the afternoon. A similar thing happens with 80 meters only later in the evening. 160 meters is frequently below the critical frequency and may not have any skip zone. The critical frequency may go as high or higher than 10 MHz during the daylight hours. Very close in sky wave propagation is possible just above, at and below the critical frequency.  

D layer absorption affects 160, 80 and 40 meters drastically during the day limiting the distance. At sunrise and sunset as the D layer is dispersing or the ions are recombining extra long distances become possible. This is called Gray line propagation as signals can travel in that zone with minimal absorption. 


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