We can estimate the distance for daytime propagation on 160m with some
rough calculations.
The followoing table gives ionospheric absorption (from Proplab Pro) on
160m at noon in winter at solar minimum for a one-hop E region path
(with daytime E region critical frequencies generally above 2MHz, all
elevation angles will be refracted back to Earth) and free space path
loss for three distances.
distance absorption free space total loss
path loss
500km 45dB 91.6dB 136.6dB
1000km 60dB 97.6dB 157.6dB
1500km 75dB 101.1dB 176.1dB
Assuming 0dBi gain antennas on both ends (roughly what a quarter-wave
vertical does over average ground at its peak) and various transmit
power levels allows us to determine the signal power at the receiver.
distance TX power RX power
500km 100W -86.6dBm
1KW -76.6dBm
1000km 100W -97.6dBm
1KW -87.6dBm
1500km 100W -126.1dBm
1KW -116.1dBm
Although our receiver sensitivity is below all of these RX powers
(typically around -130dBm), our real sensitivity is limited by external
noise. Thus your mileage (literally) will vary depending on your noise
environment and if you have better antennas.
Again, these are simply ballpark figures. And they do not account for
the day-to-day variablility of the lower ionosphere. Some days will
likely be better, some days will likely be worse.
Carl K9LA
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