• Bistatic pulse compression HF sounder
• 3-12 kHz bandwidth
• PC-based, with extensive use of digital signal processing techniques
• Uses commercially available equipment
• GPS system timing to ensure remote stations are synchronised

DAMSON measures the channel scattering function which, for each propagation mode, provides:

• Doppler shift
• Doppler spread
• Absolute time of flight
• Multipath spread
• Signal strength
• Signal to noise ratio (SNR)

The above display shows 12 kHz DAMSON data from a disturbed near vertical incidence skywave (NVIS) path from Harstad to Abisko on 10 Oct 1999. The main feature of the display is the scattering function which shows the reeived power plotted against delay time and Doppler frequency axes; below and to the side are the multipath and Doppler profiles of the scattering function. Also displayed are a time of flight (TOF) multipath profile and a CW frequency measurement which offer increased measurement ranges over the scattering function. A noise measurement is also included.

HF Channel Sounding Usage

• Robust waveform selection
  • Allows operation of HF in stressed conditions
  • Requirements based on high latitude DAMSON masurements
• Automatic radio control system
  • Allows high availability of HF communications for low workload
  • Information provided on channel probing techniques
• HF simulators
  • Allow rapid development of modems through cost effective and reproducible testing
  • Improve specification of simulator test parameters
  • Provide estimate of modem availability by mapping channel measurements to model performance surfaces
• Modem development
  • Development of high data rate modems to meet long term aim of 16kbps in narrowband channels
  • Development of wideband systems with data rates up to 64kbps
  • Provide direct comparison between modem operation and channel characteristics by interleaving modem and channel sounder transmissions

Click on image to run animation (2.8MB)

DAMSON data has been used to simulate on air testing of three different 75 bps modems. Modem performance surfaces (lower panel) represent the SNR required for each modem to achieve a bit error rate of 10^-3 for specified multipath and Doppler spreads. These examples show the results of a test using 3 kHz data from a 24-hour period on a path from Harstad in Norway to Kiruna in Sweden. For each measurement the overall Doppler spread, the overall multipath spread, and the SNR are obtained. These parameters are then tested against each of the modem surfaces. If the SNR exceeds that required for the specified Doppler and multipath spreads, a green mark is plotted and the test counts as a pass. If the resulting point is below the surface, a red mark is plotted and the test is a failure. Cumulative percentage availability statistics are displayed for the three modems.

See also:
HF Channel Sounding
WHISPER – Wideband HF Ionospheric Sounder for Propagation Environment Research