Some Frequently Asked Questions about WACARS

Why don't I see aircraft on the map?

Firstly make sure the option is enabled on the Options menu. Also check that the co-ordinates of your map cover the area you are interested in. Most importantly, an aircraft will only be plotted is it sends it's position in the body of the message. For example,

N312UA B737-322 23673/1479 1412 DEMS
United Airlines UA1649 Calgary-SanFrancisco
Using Ground Station 2

will plot planes on a map at, 50362N, 114370W, 50331N, 114417W 50283N, 1144861W and 49539W, 115296W.

I get loads of raw data but it's all rubbish. Why don't I see any decoded results? Other decoders work, why doesn't WACARS?

It took quite a while to discover the reason for this and even longer to prove it. All signal processing software requires an accurate source of timing information with which to process the data. The following is part of an email conversation I had with S. Waits:-

I've found that my sound card (Gravis UltraSound PnP) "rounds" the
recording sample rate to its next higher "allowable" sample rate. So,
when I sample at 14400, it rounds to 16000.

This rounding is more than enough to upset the decoder and spoil the decoding. Unlike DOS based decoders WACARS doesn't know anything about the soundcard and it's set-up. It just makes an operating system call to as for a sound stream at the appropriate sample rate. If the sound driver has rounded the sample rate WACARS will never know. It is this which causes the problems.

How do I know if I'm tuned to the right frequency?

You should hear sounds like this - CLICK HERE[N779.WAV - MISSING]. This sample also gives you an idea of the sort of quality and signal to noise ratio you need too. If you have much more background noise than is present in this sample then you need to think about taking steps to reduce it.

WACARS runs great for about 5 minutes, but then the hard disk light comes on and the machine gets slower and slower, then hangs and I have to re-boot it. What's going on?

This is caused by your sound card drivers. The solution seems to be to re-install them. Use Control Panel to remove the drivers for your soundcard then re-boot your machine. Windows will realise that it has no drivers for the soundcard and re-install them. Most people who've had this problem have found that this cures the problem.

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