Lowest Usable Frequency (LUF)
vs. Thickness of Ducting Layer


NOTES

For surface-based ducts, the thickness of the duct = the height of the inversion.

For elevated ducts, the lower boundary of the duct is usually less defined than the upper boundary (the inversion level), so LUF determination is less reliable.

Unlike an ionospheric skip MUF (maximum usable frequency) which is a sharp hard frequency limit determined by the critical angle, the ducting LUF instead is a soft frequency limit below which a gradual decline in signal strength occurs.


Duct Thickness
LUF
Feet
Metres
Band
Frequency
50
15
W
11.67 GHz
100
30
W
3.35 GHz
150
46
UHF
 1615 MHz
200
61
UHF
962 MHz
300
91
UHF
464 MHz
400
122
VHF
276 MHz
500
152
VHF
185 MHz
600
183
VHF
133 MHz
700
213
VHF
101 MHz
800
244
VHF
79 MHz
900
274
VHF
64 MHz
1000
305
VHF
53 MHz
1100
335
VHF
45 MHz
1200
366
VHF
38 MHz
1300
396
VHF
33 MHz
1400
427
SW
29 MHz
1500
457
SW
26 MHz
  

2000 Updated 2020 William R. Hepburn  www.dxinfocentre.com