South Atlantic WSPR Stations Track Equatorial Propagation
Back to NewsAmateur radio stations on St. Helena and Ascension Island are providing measurements of HF propagation near the geomagnetic equator, with early observations showing recurring nighttime frequency shifts on the path between them. The installations extend WSPR monitoring into a region with ionospheric behavior different from the midlatitude paths familiar to many operators.
In an October 7 report, HamSCI described equipment supplied by Gerry Bulger, G3WIP, for Garry Mercury, ZD7GWM, on St. Helena, followed by a receiver Bulger installed on Ascension under his local callsign, ZD8GB. St. Helena also gained a GPS-locked WSPR transmitter.
Nighttime Measurements Draw Research Interest
Gwyn Griffiths, G3ZIL, is examining Ascension’s reception of the St. Helena transmitter on 3.5 MHz. He reported daily Doppler patterns around local midnight and earlier in the evening, suggesting possible connections to changes in the equatorial ionosphere after sunset.
The interpretation remains preliminary. Ascension lies close to the geomagnetic equator, while St. Helena is farther south, beyond the region known as the equatorial ionization anomaly. Their locations make the inter-island path useful for investigating these low-latitude effects.
WSPR Reports Include More Than Signal Strength
WSPRdaemon, the receiving software used at the sites, decodes Weak Signal Propagation Reporter transmissions and records noise estimates alongside reception reports. Its measurements can help separate changes in a distant signal from changes in the receiver’s local noise environment.
The software’s measurement definitions include received frequency, signal-to-noise ratio, frequency drift, and timing offset. Those measurements provide several ways to examine how reception changes over time, rather than relying only on whether a signal was decoded.
Frequency stability is particularly important for Doppler work. A GPS-locked transmitter reduces one source of variation, allowing smaller changes elsewhere in the path to be studied. Receiver drift can still contribute to the measured frequency change. Timing offsets can likewise include clock errors and delays in the transmitting or receiving audio systems.
Island Sites Still Face Local Interference
HamSCI reports that the Ascension installation receives WSPR despite substantial interference from local electrical equipment. The site illustrates the need to measure receiving conditions alongside propagation.
WSPRdaemon estimates noise at the same times and frequencies as its signal reports and makes the resulting data available for analysis. Together, the frequency, noise, and reception records support comparisons across repeated observations as researchers investigate the South Atlantic path.
Sources and Further Reading
- HamSCI: WSPR Activity in the Southern Hemisphere
- WSPRdaemon Project
- WSPRdaemon Measurement Field Definitions