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Updated Audio Receivers (markdown)

Brumi-2021
2025-03-07 23:16:56 +01:00
parent ed0cdd615b
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Audio-Receivers.md

@@ -7,7 +7,13 @@ The Audio App is the main way that signals can be heard and seen in detail. Thre
* **NFM:** The Narrow Band Frequency Modulation decoding ITU Classification: FM3
* **WFM:** 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 .
Hackrf has poor sensitivity to receive directly those HF Wefax signals, (mainly broadcasted in HF : 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)](https://www.sigidwiki.com/wiki/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. https://www.sigidwiki.com/wiki/WEFAX
The Key Items on the App that can be seen or selected with the cursor and changed with the encoder knob are:
@@ -36,6 +42,12 @@ 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 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 . Still our mayhem is not decoded the picture. Coming soon)
![image](https://github.com/user-attachments/assets/3b76e009-d64f-495f-8976-1858502248ec)
![image](https://github.com/user-attachments/assets/58acad5c-5abe-4b2b-858f-eb8aed06a228)
* **WFM:** There are three option filters in that Secondary settings :
* (1) 200k ,the original filter for commercial FM stations with soft transition,