Typical Spectrogram

Title: Typical Spectrogram

Contributed by: Bob Mattaliano N6RFM

Reviewed by:

Receiving Station Location: EM12jw, near Fort Worth, TX 16January2026

Receiving Station Details: Grape-1 DRF

Feature Description

WWV 10MHz 16January2026

Typical GRAPE spectrogram measuring propagation on 10 MHz from WWV to EM12jw over a 24-hour period. The most prominent features (darker red lines) are the reception path closing (A) at ~0045Z (~one hour after local sunset) and opening ~1345Z (~15 minutes after local sunrise). For additional context, that day the Solar Flux was 10.7 indicative of moderately high solar activity and good HF ionization, especially daytime MUF support. The Geomagnetic Kp Index was in the range of ~4–6 (unsettled to active). Details regarding other spectrogram features will be described in the other examples.