High‐resolution probing of the HF ionospheric skywave channel: F 2 layer results

An HF propagation link via ionospheric reflections has been established for several years between Platteville, Colorado and Urbana, Illinois at a separation distance of 1,401 km. Although the probe is wideband in nature, covering the frequency range from 5 to 15 MHz, the transmitter is capable of transmitting two sets of CW waves at a frequency separation as narrow as 2 Hz. The signals are coherently received. Since the receiver bandwidth is 50 Hz, a beat is observed if the frequency separation is less than 50 Hz. In this case the spectra so computed and plotted would show two clear and separated peaks. The phase information can be extracted which is used to investigate the propagation delay and Doppler shift. The variation of propagation delay and Doppler shift with time gives delay spread of about 17 μs and Doppler spread of about 0.1 Hz for this midlatitude path. These spreads are important characteristics for a fading channel.

Section: Resultsmentioning

confidence: 99%

Section: Summary and Discussionmentioning

confidence: 99%

Probing the ionosphere with an extremely narrow frequency separation

Lin¹,

Yeh²,

Wong³

et al. 1995

“…MITRE [ Clune et al ., 1991; Perry and Rifkin , 1989, 1991; Rifkin and Perry , 1990], NRL [ Wagner and Goldstein , 1985; Wagner et al ., 1987, 1988], and SRI [ Basler et al ., 1988] have conducted WBHF propagation measurements in order to characterize the WBHF channel. The measurements presented here add to this database.…”

Section: Introductionmentioning

confidence: 99%

Measured channel parameters for the disturbed wide‐bandwidth HF channel

Nissen

Bello

2003

[1] The wideband HF (WBHF) channel impulse response measurements presented here were taken over a high-latitude auroral path using the MITRE experimental WBHF test facility. A nominal instantaneous bandwidth of 1 MHz was used for the majority of the tests. These tests took place from 14 March through 1 April 1992 over a path from Sondrestrom AFB, Greenland, to Bedford, Massachusetts, a distance of approximately 3,100 km. The measurements were made using a direct-sequence pseudo-noise (DSPN) channel probe with a (Ϯ180Њ) chip modulation and chip rate of 1024 kchips/second. Complex channel impulse response values at increments of 500 nanoseconds in delay were derived by correlating the received signal with a set of local DSPN references uniformly spaced in delay over a delay range of 2 ms. Each of these channel impulse response values was sampled in time at a rate of up to 62.5 samples per second, resulting in the ability to observe (one-sided) Doppler spectra and shifts of up to 31.25 Hz. From these measurements, the channel scattering function, rms (2) Doppler spread, rms (2) Delay spread, Doppler shift, and rms (2) spread factor were calculated. In addition, for the first time, the impulse response correlation along the delay axis was calculated. These latter measurements support the use of an uncorrelated scattering hypothesis in modeling the disturbed WBHF channel.

“…Recently there has been interest in propagating wideband signals through the ionosphere [Wagner and Goldstein, 1985]. In their experiments, the original 1-gs pulse is found to be severely stretched and split into two magnetoionic components.…”

Section: Introductionmentioning

confidence: 99%

“…This bandwidth comes about because of the dispersive nature of the ionosphere. This quantity may be called the dispersive bandwidth of the ionosphere as has been used by several authors [Wagner and Goldstein, 1985]. As to the precise value of b, it depends on one's definition.…”

Section: Introductionmentioning

confidence: 99%

Vertical ionograms and dispersive bandwidth for an oblique path

Lin¹,

Yeh²,

Soicher³

et al. 1989

The ionosphere is known to be a dispersive medium. Additionally, for a fLxed ground distance in an oblique propagation geometry, the ray of each Fourier component of a pulse follows its own path in a phenomenon known as frequency splitting. As a consequence of these two factors distortion results. Under the approximation of a quadratic phase channel, this distortion is most conveniently characterized by a quantity, known as the dispersive bandwidth. Formulas for the dispersive bandwidth have been derived both for the linear layer and the parabolic layer and are given without showing derivations. A technique has been developed to analyze the vertical ionogram for dispersive bandwidth. This technique has been applied to several days of digital ionosonde data. The resulting values of dispersive bandwidth are reasonable and plotted over a diurnal cycle. Such a technique should be further developed as a step toward eventual application to ionospheric informatics.