Magnificient FDM-S3: the Millihertz Magnifier
With Elad’s FDM-S3 SDR now hitting the market, we have a receiver at hand which is supported by an OCXO/ GNSS frequency reference. This combines short-time accuracy with long-time stability and allows for precise frequency measurement in the millihertz range (under 30MHz). Exploiting this feature is as exciting as it is innovative. With this new tool, also a new kind of DXing is evolving. One example is propagation analysis. See below the 24h spectrogram of Radio Gotel from Jabura/Nigeria on its exclusive channel of 917kHz:
What surprises, is both, the late fade out at around 07:30UTC and the early fade-in as early as 15:20UTC. It is important to note that you here see the carrier with a resolution bandwidth of 0.0009Hz, roughly just one millihertz. The gain, compared to a listening bandwidth of 10 kHz, is a whopping 70dB, allowing extreme DX. Audio starts to emerge only from around 18:00UTC. As DX Atlas shows, the whole path between my location and Radio Gotel is under daylight at the palpable fade-in at around 15:20UTC, see screenshot below.
As with all new things: “We’ve only just begun”, Carpenters, 1970. To be continued.