Receiving weather fax pictures on HF using fldigi

A week or so ago I saw a weather fax (WEFAX) picture someone had posted that they’d captured on HF. This grabbed my attention because I like maps and I like to see things to do with the weather. I’d tried a couple of years ago to receive satellite weather pictures with little success (due to a very poor aerial) and the idea that I can receive weather maps on HF intrigued me.

After very little searching, I discovered that fldigi can receive fax pictures. I use fldigi for operating data contests so I’m very familiar with it. I soon had it configured correctly and so the next stage was to find what frequency the WEFAX pictures are transmitted on. A quick search around and an ask via Twitter pointed me towards this document which lists various transmitting stations around the world. There are two in Europe that I decided to try listening for, one in the UK at Northwood and the other in Hamburg, Germany.

I first started listening on the UK frequencies but heard nothing so I switched over to Germany and over the course of the week, I received a lot of pictures. The 3,855.000 kHz signal seemed about the best for me here. This morning I switched to the Northwood frequency of 4,610.000 kHz and very soon the pictures started rolling in.

fldigi receiving a WEFAX image from the Northwood transmitter
fldigi receiving a WEFAX image from the Northwood transmitter

If you want to use fldigi to receive WEFAX, you need to do the following:

Op Mode / WEFAX / WEFAX-IOC576
If you are receiving signals from Germany then the shift is 850Hz instead of the default 800Hz. This is changed through Configure / Operating / Active Modem, select the Other tab on the second row and then the Wax tab below it. For Germany, put 850 in the Frequency shift box or leave it at 800 for UK reception. If you switch between the two transmitters, remember to change this figure. Make sure you hit the Save box at the bottom.

Set LPM (lines per minute) to 120 in the box below the receive window.

For UK reception, I’ve found the Slant figure needs to be at 0.0071 and for Germany, set it to 0.0118. This is to ensure the picture is vertical and doesn’t slant.

Most sites I’ve found suggest tuning your radio to 1.9kHz below the transmit frequency but it really doesn’t matter, as long as you have a good signal in the waterfall and you set the two red vertical lines on top of it. My radio ‘sweet spot’ is at 1,500Hz so I tune 1.5kHz below the transmit frequency and set the radio filter down to 1,000Hz as can be seen above.

That’s it! Tune your wireless in to one of the frequencies in the list I posted above and wait. You’ll soon have an image folder full of stuff like this.

You can click on any of the images above for a higher quality version.

Receiving WEFAX maps is very straightforward, quite simple to do and can produce some good results. Not all pictures I’ve received are as good as above but on the whole, I’m very pleased with how easy this has been.

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