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Receiving WeatherFax maps

Following a query we received from a ham visiting the UK from abroad I thought I'd have a go at receiving short-wave weather map transmissions. It turned out to be surprisingly easy if you already have your rig connected to a PC for data modes. You don't need CAT or anything complex so you could probably get away with a simple audio lead connecting your rig headphone socket to your PC's mic or line input socket.
 
The WeatherFax map transmissions appear to be aimed at mariners who may not have access to satellite phone data. A large number of different maps are transmitted, including surface prognosis (forecast!), wind direction, sea ice etc, etc.  

There is a worldwide network of WeFax transmitters - see http://info.yachtcom.co.uk/weather.php for a list. Our 'local' transmitter is GYA, a Royal Navy station transmitting met office maps. Its nominal location is Northwood but it is physically located in nearby Eastbury, Herts. It uses a number of frequencies, including 2.6185 MHz, 4.610 MHz, 8.040 MHz, 11.0865 MHz and allegedly 18.261 MHz, although online sources suggest the latter is *no longer in use.
 
To receive the signals you need to set your receiver to USB, tuned 1.9 kHz BELOW the wanted frequency, so the frequencies to tune to are:
 
  MHz
2.6166
4.6081
8.0381
11.0846
18.2591*
 
The GYA transmission schedule is available online but I received maps at times the transmitter wasn't listed as being on-air. There were some lengthy gaps between map transmissions so it is worth leaving your rig & PC on even if you can't hear anything initially.

Decoding the signals requires WeFax-compatible software. Fortunately FLdigi, the free data-modes package decodes Weather Fax transmissions, so once installed it was simply a matter of selecting WEFAX-IOC256 from the Op Modes menu:

 
I tuned to 4.608 MHz mid-afternoon using my Kenwood TS-590D and 10m vertical. Signals on the rig were S9+20 when reception started, which was good news as the noise level on that frequency was S9. Occasional fades can be seen as horizontal bands on the map below.

The WEFAX modes in FLdigi nominally benefit from AFC, so I didn't need to adjust my tuning or click on the waterfall to tune signals in but decoding started earlier if I clicked on the signal in the waterfall. When tuned 1.9 kHz low the signal seemed to spread between 1.5 and 2.4 kHz, although the edges weren't well-defined:



So what do the maps look like? All a bit handmade really, but no doubt full of safety-of-life critical information. Here is a sample:


Click on the map to see it in greater detail


The title of the map is near the top, which is a shame as FLdigi seemed a bit slow latching onto the signals. Unfortunately this lost the heading of most of the maps I received. FLdigi automatically saves the maps as png files and you can click on the filename within FLdigi to see a preview.

Let us know via the cub email reflector if you have a go at WeFax reception!

73

Mike
G4RAA

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