A comparison of long-distance HF radio-signal reception at high and low receiving sites

High-frequency radio signals transmitted over two separate 10,000-km temperate-zone paths were received over 1-month periods at sea level and at elevated sites. Five frequencies were transmitted from Okinawa to Malta and one frequency from Puerto Rico to Hawaii. A comparison of the signal strengths indicates that high antenna siting provides definite advantages over low siting for long-distance communication. Antennas at the high sites, which were located an average of 700 ft above the low sites, received greater signal strengths than those at the low sites, the amount of signal strength advantage (as much as 10 dB) decreasing with increasing frequency. The higher sites were also less susceptible to temporary signal-strength reductions. When signal strengths were in the process of rising and falling as a result of the change of the MUF in the morning and evening, respectively, high antennas provided up to 1½ hr more receiving time for a specified signed threshold.