Topband: estimating daytime distances

[Carl K9LA]

  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