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Updated Audio Receivers (markdown)

Brumi-2021
2025-03-09 18:10:11 +01:00
parent ce1a2c5207
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Audio-Receivers.md

@@ -9,9 +9,9 @@ The Audio App is the main way that signals can be heard and seen in detail. Thre
* **WFFM:** The Wide FM Receiver is a Sub-Application of the Audio Receiver Application. Its purpose is to Demodulate and Record RF Signals modulated using the Frequency Modulation scheme. It can demodulate mono and stereo Wide FM signals of 200KHz bandwidth. Such signals are commonly used for VHF FM Broadcast services. * **WFFM:** The Wide FM Receiver is a Sub-Application of the Audio Receiver Application. Its purpose is to Demodulate and Record RF Signals modulated using the Frequency Modulation scheme. It can demodulate mono and stereo Wide FM signals of 200KHz bandwidth. Such signals are commonly used for VHF FM Broadcast services.
* **AMFM:** Wefax (HF Weather Fax demodulation) . It demodulates the weather fax maps , and sends the demodulated low scan map APT signal to the speaker (just for our audio tuning reference ) and it can be RECORD into audio.wav contents file with our portapack-mayhem . (SR =12KHZ, audio mono track). The signal is broadcasted in USB mode , but the fax map , is transmitted as low scan data (white / black dot pixel ) , inside audio baseband spectrum , through a sub-carrier audio tone , modulated in FM with the low scan APT map signal . * **AMFM:** We are combining in that demodulation , two consecutive demodulations. First RF USB audio baseband demodulation , and later demodulating the FM subcarrier audio baseband tones.That modulation , it is commonly used in Wefax (HF Weather Fax transmissions) . It demodulates APT signal of the HF weather fax maps. , and sends the demodulated low scan map APT signal in parallel to the speaker (just for our audio tuning reference ) and it can be also RECORDED to the SD card , through audio.wav file (SR =12KHZ, audio mono track).
(Audio Baseband with fsc (1900Hz) FM mod +-400Hz ; Shift White pixel +400 Hz = 2.300 Hz , Shift Black pixel -400 Hz = 1.500 Hz) Inside audio baseband spectrum , there is a sub-carrier audio tone , modulated in FM with the low scan APT image map signal .
(Audio Baseband with f_subcarrier fsc (1900Hz) FSK mod +-400Hz ; Shift White pixel +400 Hz = 2.300 Hz , Shift Black pixel -400 Hz = 1.500 Hz)
Hackrf has poor sensitivity to receive directly those HF Wefax signals, (mainly broadcasted in HF band : 3 Mhz to 16 Mhz) Hackrf has poor sensitivity to receive directly those HF Wefax signals, (mainly broadcasted in HF band : 3 Mhz to 16 Mhz)
Normally we should better add a front up-converter with better HF pre-amplifiers and a reasonable small HF antenna. Normally we should better add a front up-converter with better HF pre-amplifiers and a reasonable small HF antenna.
@@ -45,9 +45,9 @@ 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. * **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. * **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. * **Gain:** The RF Amp settings. The Spectrum view is +/-20k.
* **USB+FM:** It is 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 . * **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 , we need to tune that published frequency applying negative offset (- 1.900Khz) , tuning and aligning the top max freq. "white" carrier (published) with top part aligned with top "yellow" mark, , as the following drawing, For a correct demodulation , we need to tune that published frequency applying negative offset (- 1.900Khz) , tuning and aligning the top max freq. "white" carrier (published) with top part aligned with top "yellow" mark, , as the following drawing,
Still current mayhem firmware can not decode the map-picture , we need external tools... But coming soon, please wait ...) Here in that Audio App we can tune , and RECORD the APT signal , but we have also another external receiver Wefax App , that combines both things : (that demodulation and its map display to the LCD or map recording into bmp file.)
![image](https://github.com/user-attachments/assets/3b76e009-d64f-495f-8976-1858502248ec) ![image](https://github.com/user-attachments/assets/3b76e009-d64f-495f-8976-1858502248ec)
![image](https://github.com/user-attachments/assets/58acad5c-5abe-4b2b-858f-eb8aed06a228) ![image](https://github.com/user-attachments/assets/58acad5c-5abe-4b2b-858f-eb8aed06a228)