RU2282881C1 - Method for measuring absolute transmission time of short radio waves in ionosphere by means of radio signals with linear-frequency modulation - Google Patents

Abstract

FIELD: radio engineering, possible use in radio location and navigation systems.

SUBSTANCE: in the method for measuring absolute transmission time of short radio waves in ionosphere by means of radio signals with linear-frequency modulation, mode structure of ionosphere short-wave channel is determined and alignment of time scales of distributed stations is performed by signals of precise time with precision up to several milliseconds, probing of ionosphere is performed in whole linear-frequency modulation range of radio complex (3-30 MHz). In accordance to synchronized program, transfer to emission/receipt mode is performed at sliding frequency with speed 100 kHz/s in more narrow range of frequencies from f_n to f_k=f_n+100KHz, i.e., "saw" mode is realized with repetition period ΔT=1s. It can be called a synchronization mode. Frequency f_n lies within range of passage frequencies and may be changes in accordance to synchronized program in process of measurements. In time moment t₀ transmitter starts, receiver at other end of radio lines starts in time moment t₀+Δt_dis, where Δt_dis - time of discrepancy of time scales of aforementioned transmitter and receiver. Differential frequency for receiver will be proportional: F₂=(df/dt)Δt_meas, where Δt_meas=t_gr-Δt_dis, where t_gr - time of group transmission from transmitter to receiver; Δt_meas=t_gr-Δt_s=0 and t_gr= Δt_s. Correction is performed during several emission cycles, during which measuring of differential frequency is performed and correction of Δt_dis is performed to provide F₂=0. At next stage in time moment t₀+Δt_s=t₀+t_gr transmitter launches. Supposing routes to be reversible, in time t_gr radio signal is received by receiver. Its differential frequency F₁ equals F₁=2t_gr(df/dt), and time of group transmission is determined as t_gr+F₁/2(df/dt).

EFFECT: possible measurement of absolute transmission time of short-wave radio signals.

2 cl

Description

The invention relates to radio engineering, is intended to measure the absolute propagation time of KB radio signals and can be used in radar and navigation systems.

A known method of measuring the propagation time of KB signals with synchronization by GPS [1].

However, in the known measurement methods, it is not possible to measure the absolute propagation time in ionospheric communication channels in the KB band, and special GPS radios are required.

The proposed method allows measurements of the absolute propagation time of KB radio signals using a radio complex with a linearly-frequency-modulated signal.

кГц/с в интервале частот от f_н до f_к=f_н+100 кГц с периодом повторения ΔТ=1 с; затем в ЛЧМ приемнике на другом конце радиолинии путем регулировки момента запуска гетеродина ЛЧМ приемника устанавливают разностную частоту на выходе ЛЧМ приемника F₂=0; на третьем этапе - режиме измерения - включают ЛЧМ передатчик на противоположном конце линии и, полагая трассы обратимыми, через время t_гр принимают радиосигнал первым ЛЧМ приемником, который будет иметь разностную частоту F1=2t_гр(df/dt), а затем определяют время группового распространения:The technical result - providing the ability to measure the absolute propagation time of KB radio signals - is achieved by the fact that a new measurement method is proposed, consisting of three stages, namely, that at the first stage — probing the ionosphere by a continuous chirp signal — the mode structure of the ionospheric KB channel is preliminarily determined, linking time scales of spaced points according to accurate time signals with an accuracy of several milliseconds and carry out sounding of the ionosphere in the entire range of the LFM radio Plexa from 3 to 30 MHz; at the second stage - synchronization - go into the radiation / reception mode at a moving frequency with a speed of df / dt = 100

kHz / s in the frequency range from f _n to f _k = f _n +100 kHz with a repetition period ΔT = 1 s; then, in the chirp receiver at the other end of the radio line by adjusting the start time of the local oscillator of the chirp receiver, set the difference frequency at the output of the chirp receiver F ₂ = 0; at the third stage - measurement mode - they turn on the LFM transmitter at the opposite end of the line and, assuming the paths are reversible, after t _t receive the radio signal with the first LFM receiver, which will have a difference frequency F1 = 2t _g (df / dt), and then determine the group time distribution:

t _gr = F1 / 2 (df / dt),

where t _gr is the time of group propagation of the KB radio signal;

df / dt - rate of change of the frequency of the chirp signal.

Figure 1 shows the structural diagram of a radio complex with a continuous LFM signal, and Fig.2 is a timing diagram of the frequency changes of the LFM transmitters and LFM receivers.

The radio complex contains the first and second reference generators, the first and second chirp synthesizers, the first and second radio transmitting devices, the first and second radio receiving devices.

Measurements are carried out as follows.

Preliminarily, in order to determine the mode structure of the ionospheric KB channel and to link the time scales of spaced points according to accurate time signals with an accuracy of several milliseconds, the ionosphere is probed in the entire range of the LFM radio complex (3-30 MHz).

Then, according to the agreed program, they switch to the radiation / reception mode at a moving frequency with a speed of 100 kHz / s in a narrower frequency range from f _n to f _k = f _n +100 kHz, i.e. the “saw” mode is carried out with a repetition period ΔT = 1 s. It can be called a synchronization mode. The frequency f _n lies in the range of transmission frequencies and may vary according to an agreed program during the measurement.

At time t ₀ in step 1, transmitter 1 starts. Receiver 2 at the other end of the radio link starts at time t ₀ + Δt _pacc , where Δt _pacc is the time difference between the time scales of transmitter 1 and receiver 2.

Then the difference frequency for receiver 2 will be proportional to:

F ₂ = (df / dt) Δt _var

where Δt _ism = t _gr -Δt _pacc ,

t _gr is the group propagation time from transmitter 1 to receiver 2. By changing Δt _pacc we must obtain the difference frequency in the second chirp receiver F2 = 0.

In this case, Δt _ism = t _gr -Δt _w = 0 and t _gr = Δt _w (adjusted).

In parentheses is the adjusted mismatch time Δt _w .

The correction is carried out over several radiation cycles (each lasting 1 s), during which the difference frequency is measured and Δt _{pacc is adjusted} to ensure F ₂ = 0 (in total, it takes no more than 30 seconds to measure F ₂ and correct Δt _w ). This procedure does not affect the measurement of the absolute propagation time of KB signals in the ionosphere, since the propagation time certainly does not exceed the repetition period of the radiation interval equal to 1 second.

In the next step, at time t ₀ + Δt _w = t ₀ + t _gr, transmitter 2 starts. Assuming the paths are reversible, after a time t _{g the} radio signal is received by receiver 1. In this case, its difference frequency F ₁ will be equal to:

F ₁ = 2t _gr (df / dt).

Thus, we measure the time of group propagation:

t _gr = F _1/2 (df / dt).

The resolution of the measurement method can be estimated by the formula:

Δt _gr = F ₁ / (df / dt).

At a frequency change rate of df / dt = 100 kHz / s (the frequency change rate of modern LFM ionosondes) and a frequency measurement accuracy of up to 0.1 Hz, the measurement accuracy can reach up to 1 μs.

The advantages of the proposed method include the fact that there is no need for expensive GPS navigation equipment, and also this method allows measurements to be made regardless of the reliability of the GPS or GLONASS satellite system.

Literature

1. www.gpsworid.com/gpsworld.

2. Patent No. 2058659 of the Russian Federation MKI N 03 19/00, Digital frequency synthesizer. / Ryabov I.V., Fischenko P.A. - Declared. 09/23/1993. Publ. 04/20/1996. Bull. No. 11.

Claims (1)

A method for measuring the absolute propagation time of short radio waves in the ionosphere using linear-frequency-modulated radio signals, which consists of three stages, namely, that at the first stage — probing the ionosphere with a continuous LFM signal — the mode structure of the ionospheric KB channel is preliminarily determined and the time scales are linked spaced points according to accurate time signals with an accuracy of several milliseconds and carry out sounding of the ionosphere in the entire range of the chirp radio complex from 3 to 30 MHz, per W rum stage - Synchronization - moving in the radiation / reception mode for moving a frequency at a rate df / dt = 100 kHz / s in a frequency range from f to f _n = f _{n to} 100 kHz repetition period? T = 1 second, then the chirped the receiver at the other end of radiology by adjusting the start time of the local oscillator of the chirp receiver, set the differential frequency at the output of the chirp F ₂ = 0, at the third stage - measurement mode - turn on the chirp transmitter at the opposite end of the line and, assuming the paths are reversible, after a time t _gr receive the radio signal first Chirp receiver, which will have RA value frequency F1 = 2t _g (df / dt), and then the group propagation time is determined 2t _g = F1 / 2 (df / dt), where t _gr is the time of group propagation of the KB radio signal; df / dt — rate of change of the frequency of the chirp signal; f _n - the initial radiation frequency; f _to - the final radiation frequency.

Images