Accession Number : ADP006879

Title :   Results of Measurements Performed on HF Backscatter for Evaluating the Influence on Short Range HF Data Links,

Corporate Author : HOOFDGROEP MAATSCHAPPELIJKE TECHNOLOGIE TNO DELFT (NETHERLANDS)

Personal Author(s) : Van Vliet, P. J. ; Van Der Vis, P. A.

Report Date : JUN 1991

Pagination or Media Count : 12

Abstract : On short range HF links, where the receiving station is relatively close to the transmitting station, reception of long delayed echoes (up to 20 Ms) may occur due to backscatter. These backscatter signals will interfere with signals received through the 'legitimate' path, which is either groundwave or nearly vertically incident skywave. Even on low data rate this time dispersion of signals may cause intersymbol interference. In order to assess the influence of HF backscatter on short range HF data links, measurements were performed. Path delays were measured using a direct-sequence spread-spectrum technique. A carrier, BPSK modulated with a pseudonoise (PN) sequence, was transmitted and the received signal was correlated with the same PN sequence. Between June 1989 and June 1990, measurements were taken over a 66 km path in The Netherlands and, simultaneously, over a 958 km path between T-he Netherlands and Norway. Different frequencies in the HF band were used. The measurement results show that especially on the short range link, long delayed echoes appear. The backscatter effect depends on propagation conditions, thus on frequency, time of day, season and solar activity.

Descriptors :   *NOISE(ELECTRICAL AND ELECTROMAGNETIC), *IONOSPHERIC DISTURBANCES, *RADIO WAVES, DATA LINKS, DELAY, DISPERSIONS, ECHOES, FREQUENCY, INTERFERENCE, INTERSYMBOL INTERFERENCE, MEASUREMENT, NETHERLANDS, NORWAY, PROPAGATION, RECEPTION, SEASONS, SEQUENCES, SIGNALS, SOLAR ACTIVITY, TIME, TRANSMITTING, HIGH FREQUENCY, BACKSCATTERING, GROUND WAVES(ELECTROMAGNETIC), SKY WAVES, COMMUNICATIONS NETWORKS, SIGNAL PROCESSING, IONIZATION TRAILS, NOISE(RADIO).

Subject Categories : Atmospheric Physics
      Radiofrequency Wave Propagation
      Radio Communications

Distribution Statement : APPROVED FOR PUBLIC RELEASE