VK2RK
Active member
When Ground wave is not a ground wave
Often when listening to radio operators communicating with each other on the 40 mtr band involving distances of a few hundred kilometres claims are made of doing so via ground wave propagation.
Armed with some knowledge of wave propagation verses frequency, the claim made on the 40 mtr band is not possible as the strength of a 7 Mhz wave over dry ground will be -30 dB uV/m at a distance of 102 Km.
What is providing that short distance path is actually the D and E layers reflecting vertical sky waves, usually the existence of such condition only happens at night providing reliable communication over short distances not the case during the day. The ionization conditions of the layers are also subject to space weather this will determine the existence of NVIS conditions during the day, not a long term reliable condition.
Citations
ITU Paper - https://www.itu.int/.../p/R-REC-P.368-7-199203-S!!PDF-E.pdf
Ground Wave definition - https://en.wikipedia.org/wiki/Ground_wave
NVIS - https://en.wikipedia.org/.../Near_vertical_incidence_skywave
Often when listening to radio operators communicating with each other on the 40 mtr band involving distances of a few hundred kilometres claims are made of doing so via ground wave propagation.
Armed with some knowledge of wave propagation verses frequency, the claim made on the 40 mtr band is not possible as the strength of a 7 Mhz wave over dry ground will be -30 dB uV/m at a distance of 102 Km.
What is providing that short distance path is actually the D and E layers reflecting vertical sky waves, usually the existence of such condition only happens at night providing reliable communication over short distances not the case during the day. The ionization conditions of the layers are also subject to space weather this will determine the existence of NVIS conditions during the day, not a long term reliable condition.
Citations
ITU Paper - https://www.itu.int/.../p/R-REC-P.368-7-199203-S!!PDF-E.pdf
Ground Wave definition - https://en.wikipedia.org/wiki/Ground_wave
NVIS - https://en.wikipedia.org/.../Near_vertical_incidence_skywave