DWD (Deutscher Wetterdienst) Weather Fax - 24th Feb 2022

The following images are a collection of weather products decoded from the DWD station DDK3 Hamburg (7880 kHz centre frequency) on the 24th February 2022. Before the images are some notes on software/hardware used for this decoding. Images have been rotated if required before uploading. As the day went on the band seemed to get more noisier, meaning certain charts are somewhat blurry. There may also be some multipath shenanigans going on as well.

Captures by Mark 2M0IIG, QTH Edinburgh

The schedule for the DWD fax service can be found here: https://www.dwd.de/EN/specialusers/shipping/broadcast_en/broadcast_fax_112016.pdf?__blob=publicationFile&v=1

A full list of worldwide Wefax services provided by the US National Weather Service can be found here: https://www.weather.gov/media/marine/rfax.pdf

Hardware/Software Setup

Hardware

Radio used was an SDRplay RSP1A (around £99 in the UK). The antenna was a QRPGuys 9:1 UnUntenna with around 10 metres of wire attached and a counterpoise (usually used for transmitting). The antenna wire is trapped by a window, and then goes to a pole outside, height is 4 metres. This is fed with around 5 metres of RG58 coax, and there are clip-on ferrites (cheap ones from Amazon, by no means an ideal setup) used to choke off the common mode current - again, this is more important when transmitting with it, really.

The SDR is connected to a standard Windows 10 laptop (HP Pavillion).

Software

I am using SDR++ to drive the RSP1A. The audio output is routed through Voicemeeter, a virtual audio cable application. FLDigi is used for decoding the signal after it exits the virtual audio cable.

I have adjusted the settings for the Wefax decoder in FLDigi to make sure that it auto-starts, has automatic frequency control turned on, and I have adjusted the shift to make sure it matches the expected +/- 425 Hz for the black/white tones. Another thing to change that may help is Correlation Rows to the maximum allowed, which is 50. This helps images with large white borders before the content kicks in to not get stopped too early by the software's image processor. The setup for DWD is below, but other services may have a slightly different shift - check first! You can measure this with the waterfall in FLDigi. The signal’s vertical lines should line up with the lines of your filter which can be moved by clicking on the waterfall clicking with your left mouse button.

Also note that when tuning in USB mode you should tune 1.9 kHz lower than the specified frequency to obtain the entire signal in the passband. For DDK3 this means a frequency in SDR++ of 7878.1 kHz.