Mathematical modeling of disprersive distortions of the wideband chirp signal during its propogation in the ionospheric radiochannel
Theoretical description of the chirp ionosonde operation has been made. Ionosonde registers spectrum sequence of window received-signal sampling. Mathematical modeling of dispersive distortions of spectra registered has been carried out.
On the shape of measured spectra of the ionosphere sounding by an FMCW signal under dispersion case
Abstract A theoretical description is given to the ionosonde operation configuration in the mode of sounding the decametric radio channel by the frequency-modulated continuous wave (FMCW). A preprocessing of the received signal is carried out using the frequency-compression method. It is shown that the result derived from processing an individual time sample is mathematically equivalent to a sounding of the radio channel by a complex-valued narrow-band impulse signal. The group delays of this signal determines maximum in the recorded spectrum. We give the formula for calculating the form of the recorded spectrum at ionospheric soundings by the FMCW signal subject to the dispersion. A formula for calculating the spectral width due to the dispersion is obtained. A comparison is made with experimental data.
Measurement of the Doppler Frequency Shift on Individual Rays Using a Chirp Ionosonde
We develop theoretically a method for determining the Doppler frequency shift on individual rays in ionospheric sounding. The method is based on using periodic chirp signals. The potential resolution and range of the measured Doppler-shifted frequencies are determined. Application of this method yields the relationship between the Doppler shift of the propagation-mode frequency and the velocity of a horizontal displacement of the hop tops along the Khabarovsk-Yoshkar-Ola radio path. Significant correlations between the mode order in the ionosphere and the Doppler shift, Doppler-spectrum width, and stationarity time of the propagation channel are found.