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Updated WeatherFax (markdown)

Brumi-2021
2025-03-23 19:49:16 +01:00
parent 1c19ef6dde
commit d70f4844fd
1 changed files with 21 additions and 1 deletions
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WeatherFax.md

@@ -13,4 +13,24 @@ That Wefax App is combining two consecutive demodulations. First RF USB audio ba
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 to the LCD display in low resolution. And it allows to the user , been able to RECORD (with START / STOP) that map in full resolution to the SD/BMP folder.
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. WEFAX's format is a derivative of the [Automatic Picture Transmission (APT)] originally developed for transmission from the polar satellites of the USA. WEFAX has 60, 90, 100, 120, 180 and 240 LPM (Lines per minute) speeds, and two IOC (Index of Cooperation) modes, IOC 576 and IOC 288. Most weather forecasts are sent in IOC 576. Our initial target would be , WEFAX-IOC576 standard.
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. WEFAX's format is a derivative of the [Automatic Picture Transmission (APT)] originally developed for transmission from the polar satellites of the USA. WEFAX has 60, 90, 100, 120, 180 and 240 LPM (Lines per minute) speeds, and two IOC (Index of Cooperation) modes, IOC 576 and IOC 288. Most weather forecasts are sent in IOC 576. Our initial target would be , WEFAX-IOC576 standard.
You can tune , inputting directly the Wefax broadcast frequency Station or pressing LOAD WeatherFax pre-setting stations , in the (tune menu). The application is in continuous display mode (trying to plot 2 lines / sec - if you select 120 lpm IOC 576 -the most common-) , and once you input the correct station frequency , you need to adjust the gain reception to the best point (through LNA :0/1, AMP , VGA) , to not saturate and not get too weak signal. If you don't amplify enough it could be darker image, or if you amplify too much, there could be much more whites. So it needs some tweaking too. Looking the screen and hearing the sound you should be able to find a good compromise tuning reception. In good setting conditions , you will start to recognise some part of the map in the screen ,
![image](https://github.com/user-attachments/assets/f252f666-9ad5-46c4-a157-95064ed6c67a)
![image](https://github.com/user-attachments/assets/515fbec2-742c-45c4-9bfb-54a97b4e084b)
Once you adjust the best gain levels, you can press START ,and it will record into SD/BMP , related decoded maps , in high resolution.
![image](https://github.com/user-attachments/assets/8d2fa901-5095-4aca-8b81-af5483d5d3bf)
Pls. find attached some captured examples,
![image](https://github.com/user-attachments/assets/6e3a58ad-cec4-4bbf-976b-d1185baa3fcb)