Last Updated on October 20, 2026 by John Berry
The GRWAVE Fortran application was for many years the standard method for calculating path loss assuming ground wave propagation.
In recent years, the ITU has deprecated GRWAVE. The current Recommendation, ITU-R P.368-10 (08/2022), names NTIA’s LFMF-SmoothEarth program as its official software.
On running both programs side by side across 1.8 to 30 MHz, both polarisations, and sea, average and poor ground, out to 500 km. LFMF agrees with GRWAVE to within about 1.5 dB everywhere, and usually much less.
The path loss calculator I’ve developed here accesses an instance of LFMF run on a virtual server. Since it uses third-party code and my server, there are some conditions around its use by visitors and these are noted below.
Technical issues
LFMF only supports antenna heights up to 50 m, so the calculator caps heights at 50 m.
In line with other calculators on this site, I focus on the calculation of a fade margin. Fade margin = Tx power – Tx feeder loss + Tx antenna gain – path loss + Rx antenna gain – Rx feeder loss + processing gain – Rx sensitivity. If the fade margin is positive, the path or link using that path will work. If it’s negative, it won’t. I’ve also included a goal seek routine to report the propagation distance for 0dB margin.
REC ITU-R P.368’s reference antenna is a short vertical monopole on perfectly conducting ground, which has a gain of 4.77 dBi. A real ground-mounted vertical will be somewhat lower gain because of ground losses. If the result is not to understate the signal by up to about 5 dB at each end, care is needed in modelling appropriate antenna gains
LFMF needs statement of surface refractivity, N_s. I’ve fixed this at 315 N-units. 315 N-units is GRWAVE’s default and the value most of NTIA’s own test cases use. Surface refractivity variation results in path loss variance of less than 1dB from 1.8MHz to 30MHz.
At short distances LFMF returns a negative path loss. I have therefore enforced a calculation limit of one wavelength.
Location margin** | Visitor-entered allowance (dB) for location variability. Negative is more cautious (towards 95% of locations), positive more optimistic (towards 5%, the DX case). <Needs description>.
Ground Wave Path Budget Calculator
Calculate the path budget for ground wave propagation (1.8 MHz to 30 MHz). Calculations run via NTIA’s LFMF model.
| Results | ||
|---|---|---|
| Path Loss | — | dB |
| System Value | — | dB |
| Fade Margin Positive = path works |
— | dB |
| Received Power | — | dBW |
| Range Search | — | |
Privacy and use
In providing this calculator, I assume that you are a bona fide licensed radio amateur who has a hobbyist interest in exploring electrical science. This calculator is provided to you free of charge without liability or guarantee.
When you use the ground wave path calculator, your IP address and the values you enter are sent for processing on an Amazon Web Services server in London. That server runs the LFMF-SmoothEarth program. They are kept in system service logs for up to 30 days, to diagnose faults, and prevent abuse, and they are deleted automatically when the logs expire. Individual entries can’t be deleted sooner. My lawful basis is my legitimate interest in providing the calculator to you and keeping it working.
If you are unhappy about the use of your data, do not use the calculator.