Aviation SELCAL Decoder
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1. I can't decode tones, even though I'm hearing them through the speaker.
Check Windows Recording mixer settings. Mic or Line input should be selected, which ever is connected to your receiver's audio. Most sound cards only one input to be selected at a time.
2. I can hear two tones, but only one is being decoded.
The first tone is too short to be captured by the decoder. There are a couple of ways to remedy this. First, if using a scanning receiver, place the unit on manual mode [disable scan]. Scanning causes the first part of the transmission to be cut off.
3. Do I have to calibrate before using the decoder?
No. In most cases, calibration is not necessary. However, if you find that tones are consistently decoded incorrectly (off by one digit), running the calibration can improve accuracy. This is intended to compensate for the internal time-base error of the sound card's clock generator.
4. Calibration or decoder is reading double the expected tone frequency.
This is a sure sign that input and/or output level is too high, causing a 2nd or 3rd harmonic oscillation. Solve this by reducing the input (recording) level, and if needed, the output (playback) level for the Wave device, if calibrating. If using the microphone input, be sure the Boost is OFF and the input level is set very low. The radio's volume control may need to be lowered if using the external speaker connection.
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