Abstract
A 1019 bit Legendre code was evaluated for use in digital ionosondes. Experimental testing was done using the Canadian Advanced Digital Ionosonde (CADI). Theoretically, the 1019 Legendre code autocorrelation function of this new sequence has very low peak sidelobe level of −32.6 dB, and the system signal‐to‐noise‐ratio (SNR) will be improved by 30 dB compared with a single pulse code. Field experiments were done near London, Ontario, Canada, using two CADIs in a bistatic arrangement with 20 km spacing. The experimental results agreed with the theoretical estimation (with ∼1 dB error), but a 10 Hz frequency difference between the two computers' reference frequencies, which showed up as a Doppler shift in ambiguity function, necessitated additional signal processing to get optimal performance. The experimental measurements showed that the system was able to get ionospheric echoes with very low power transmission (1 W peak) at a quiet receiving site because of the high system SNR.
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