Accession Number:

ADP006879

Title:

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

Descriptive Note:

Corporate Author:

HOOFDGROEP MAATSCHAPPELIJKE TECHNOLOGIE TNO DELFT (NETHERLANDS)

Personal Author(s):

Report Date:

1991-06-01

Pagination or Media Count:

12.0

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.

Subject Categories:

  • Atmospheric Physics
  • Radiofrequency Wave Propagation
  • Radio Communications

Distribution Statement:

APPROVED FOR PUBLIC RELEASE