TheArchive/mayhem-firmware
1
0
Fork 0
mirror of https://github.com/portapack-mayhem/mayhem-firmware.git synced 2025-11-15 17:12:52 +00:00
Code Issues Packages Projects Releases Wiki Activity

Updated Audio Receivers (markdown)

Brumi-2021
2025-04-11 23:29:04 +02:00
parent 5b7f033372
commit 4576bac676
1 changed files with 1 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
Audio-Receivers.md

@@ -12,7 +12,7 @@ The Audio App is the main way that signals can be heard and seen in detail. Thre
* **AMFM:** Here in that Audio App we can tune , and RECORD the APT signal from a HF-Weather Fax map Broadcasting Station into audio_format_APT_file.wav ,mainly for investigation , debugging , and check signal levels (signal strenght , saturation , filters check ,...). But we have also in Mayhem fw , another external receiver [Wefax App](https://github.com/portapack-mayhem/mayhem-firmware/wiki/WeatherFax) (based on that AMFM demodulation engine) , more convenient to the user, because it combines both things : (that APT demodulation and the additional display weather map to the LCD (in low resolution) able to record the decoded weather map into a bmp file (in full received resolution. -much better than the displayed in the low resolution screen) * **AMFM:** Here in that Audio App we can tune , and RECORD the APT signal from a HF-Weather Fax map Broadcasting Station into audio_format_APT_file.wav ,mainly for investigation , debugging , and check signal levels (signal strenght , saturation , filters check ,...). But we have also in Mayhem fw , another external receiver [Wefax App](https://github.com/portapack-mayhem/mayhem-firmware/wiki/WeatherFax) (based on that AMFM demodulation engine) , more convenient to the user, because it combines both things : (that APT demodulation and the additional display weather map to the LCD (in low resolution) able to record the decoded weather map into a bmp file (in full received resolution. -much better than the displayed in the low resolution screen)
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). 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).
Inside audio baseband spectrum , there is a sub-carrier audio tone , modulated in FM with the low scan APT image map signal . 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) (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). For better usability , in both Applications (this Audio App AMFM mode, and Wefax App) we are internally applying a proper tune-offset . Therefore you just need to tune the official published Weather Fax frequency transmitter. (example 3.855 Khz ,7.880 Khz , 8.040 Khz ,...).
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 add to the Hackrf receiver a front up-converter with better HF filtered pre-amplifiers, and a reasonable good enough HF antenna. Normally we should add to the Hackrf receiver a front up-converter with better HF filtered pre-amplifiers, and a reasonable good enough HF antenna.