sdrangel/plugins/channelrx/demodatv

ATV demodulator plugin

Introduction

This plugin can be used to view amateur analog television transmissions a.k.a ATV. The transmitted video signal can be black and white or color (PAL, NTSC) but only the black and white levels (luminance) is retained and hence image is black and white. There is no provision to demodulate the audio subcarrier either. The modulation can be either AM or FM. A plugin supporting audio can be used in the same passband to demodulate an audio carrier but not a subcarrier which excludes FM.

The whole bandwidth available to the channel is used. That is it runs at the device sample rate possibly downsampled by a power of two in the source plugin. It expects an integer number of MS/s and standard image quality requires a sample rate of at least 4 MS/s. The Airspy Mini 3 MS/s mode may still be acceptable. Anything below should be considered experimental quality.

Interface

1: Image

This is where the TV image appears.

2: Modulation

• FM1: this is Frequency Modulation with approximative demodulation algorithm not using atan2
• FM2: this is Frequency Modulation with less approximative demodulation algorithm still not using atan2
• AM: this is Amplitude Modulation

For FM choose the algorithm that best suits your conditions.

3: Frames Per Second

This combo lets you chose between a 25 FPS or 30 FPS standard.

• 25 FPS corresponds to the PAL 625 lines standard (PAL B,G,I,L)
• 30 FPS corresponds to the PAL 525 lines standard (PAL M)

4: Horizontal sync

Check/uncheck this box to toggle horizontal synchronization processing.

5: Vertical sync

Check/uncheck this box to toggle vertical synchronization processing.

6: Half frames

Check this box to render only half of the frames for slow processors.

7: Reset defaults

Use this push button to reset values to a standard setting:

• FM1 modulation
• 25 FPS
• Horizontal and vertical syncs active
• Interlacing
• 100 mV sync level
• 310 mV black level
• 64 microsecond line length
• 3 microsecond sync length

8: Synchronization level

Use this slider to adjust the top level of the synchronization pulse on a 0 to 1V scale. The value in mV appears on the right of the slider. Nominal value: 100 mV.

9: Black level

Use this slider to adjust the black level of the video signal on a 0 to 1V scale. The value in mV appears on the right of the slider. Nominal value: 310 mV.

10: Line length

This is the line length in time units. The value in microseconds appears on the right of the slider. Nominal value: 64 microseconds.

10: Top length

This is the length in time units of a synchronization top. The value in microseconds appears on the right of the slider. Nominal value 3 microseconds.