In daylight the D-layer forms and absorbs 7 MHz over any distance. But straight up and straight back down still works — signals leave at a steep angle, bounce, and land 100 to 300 miles away.
WHY TWO COMPLETELY DIFFERENT BANDS, DAY AND NIGHT
In daylight the D-layer forms and absorbs 7 MHz over any distance. But straight up and straight back down still works — signals leave at a steep angle, bounce, and land 100 to 300 miles away. That trick is called NVIS, and it is why emergency and state-wide nets live on 40 in the afternoon.
Within an hour of sunset the D-layer dissolves and the same band reaches across oceans.
Summer brings static crash from distant thunderstorms. Winter nights are quieter and far better.
WHEN IT WORKS
BEST · Sunset to sunrise for distance · daytime for 300 milesWORST · Summer nights, storm staticWATCH · D-layer dies ~1 hr after sunset
WHO MAY TRANSMIT WHERE · 47 CFR §97.301
FREQUENCY (MHz)
MODE
LICENSE CLASS
7.000–7.025
CW
Extra
7.025–7.125
CW — Novice & Technician
Technician and above, General, Advanced, Extra
7.125–7.175
Voice
Advanced, Extra
7.175–7.300
Voice
General, Advanced, Extra
Is 40 meters open right now? The Ham Radio IQ app shows the MUF and LUF over your head this minute, whether this band is above or below them, and a map of real contacts being heard worldwide. See the board →