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70 YEARS AGO, Lincoln Laboratory investigated high-frequency (HF) ionospheric scatter techniques to improve long-range communications. The work on HF ionospheric scatter showed that, in the frequency range of 20 to 50 MHz, ionospheric-scatter transmissions could be useful for point-to-point narrowband communication of up to 1000 miles. At distances of less than 350 miles, differential time delays due to interference limited the useful bandwidth. High-frequency ionospheric scatter communications never became widely used except for the DEW Line rearward link. Fading and low channel capacity remained problems. The Laboratory ended study of HF scatter in 1955.
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