HF Field Strength Prediction for Short and Medium-Range Ionospheric Radiopaths 
B.G. Barabashov, M.M. Anishin, and L.P. Radio 
 
The method is described of evaluation of sky-wave field strength. The method 
provides a tool for planning and operation analysis of HF radio links ranging up 
to 6000 km. The special attention is given to short radiopaths. The method is 
implemented as a software package. 
The package allows: 
- to predict space-time distribution of ionization along an ionospheric 
radiopath, and adjust the distribution using current diagnostics data; 
- to determine the modal and ray structure of incoming field at the reception  
site, including lower, upper rays and complex  trajectories, and expected number 
of rays (modes) and times of their relative delay; 
- for every ray (ordinary and extraordinary), to evaluate the following 
characteristics: elevation angles (launch and arrival), group delay, ionospheric 
absorption, space loss, Earth reflection loss, parameters of polarization 
ellipse for outgoing wave; 
- to evaluate total signal strength at the reception site, and compute effective 
voltage of signal at a receiver input; 
- to predict  MUF, FOT, and LUF for a path; 
- based on specific propagation conditions, to make a selection of optimal 
antennas; 
- to predict areas of reliable reception, and depict the results on world map. 
Effectiveness of the method was experimentally tested for the most 
propagationally-complicated conditions – short-range paths in between 15 … 600 
km. The experiment could be characterized as measuring average HF field strength 
with calibrated transmitter-receiver circuits. The experiment involved years of 
maximum and low solar activity. Furthermore, experimental variations were 
compared with the results of simulation modeling. At the same time, the 
possibility was estimated of using ITU-R (R.533-8) and ICEPAC packages for loss 
prediction at short paths. 
The results of experimental testing showed quite high accuracy of the proposed 
method. The rms error of prediction of effective values of HF field strength 
proved to be close to instrumental error of measuring equipment, current 
diagnostics data being involved. Meanwhile, ITU-R (R.533-8) and ICEPAC 
predictions for the same conditions were found to be in significant error.