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Updated Audio Receivers (markdown)

Brumi-2021
2025-03-19 23:18:53 +01:00
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Audio-Receivers.md

@@ -48,10 +48,10 @@ The Key Items on the App that can be seen or selected with the cursor and change
* **AM:** Bandwidth settings of DSB 9k, DSB 6k, USB+3k, LSB-3k, CW. The Spectrum view is +/-20k.
* **NFM:** Bandwidth Settings of 16k,11k,8k5. Note there is no setting for the more common 6k5 used in European Spectrum plans. Next item is SQ: which is shown in the format of 40/99 allow the noise squelch point to be set Between 0-99. Typically, around 40-50 is a good threshold.
* **Gain:** The RF Amp settings. The Spectrum view is +/-20k.
* **USB+FM:** It is usually used to demodulate Wefax (HF Weather fax transmissions) , demodulating the signal in two steps, first demodulating the tuned RF signal in USB , extracting audio tones. And then demodulating again those FM modulated subcarrier audio tones, to extract APT low scan weather fax map signal. (that signal can be recorded into audio.wav file .
For a correct demodulation ,currently we need to tune that published frequency applying negative offset (usually - 1.900Khz ,in our case , optimum with -2.200Khz ) , tuning and aligning the top max freq. "white" carrier (published) with top part aligned with top "yellow" mark, , as the following drawing. (that automatic -offset will be added in next PR )
Here in that Audio App we can tune , and RECORD the APT signal ,mainly to check signal strenght , and for investigation and debugging .
But soon , we will have also another external receiver Wefax App , that combines both things : (that demodulate and display map to the LCD or records it into bmp file.)
* **USB+FM:** It is usually used to demodulate Wefax (HF Weather fax transmissions) , demodulating the signal in two steps, first demodulating the tuned RF signal in USB , extracting audio tones. And then demodulating again those FM modulated subcarrier audio tones, to extract APT low scan weather fax map signal. (that signal can be recorded into audio.wav file ).
For a correct demodulation ,currently we need to tune that published frequency , (in our application , you do not need to apply any usual - 1.900Khz offset . The -tuning offset , is already applied internally). So we have to just tune the (published) frequency directly .
Here in that Audio App we can tune , and RECORD the APT signal into file.wav ,mainly for investigation and check signal levels (signal strenght , saturation , filters check , debugging). But we have also another external receiver Wefax App , more convenient to the user, that combines both things : (that APT demodulation and the additional display weather map to the LCD (in low resolution) or records the receiver map into bmp file (in full resolution.)
![image](https://github.com/user-attachments/assets/de140ed5-bbc9-4aa4-b775-4e7cae36ead0)