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Can fsk send video over radio waves?

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dl09

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Can frequency shift keying be used to send live video over radio waves? At say a resolution of 240 x 460 pixels and 15 frames per second? The images are black and white.
 

Yes but its not a trivial design to get the filtering/tone detection right as the
speeds needed challenge the filter accuracy and stability needed. The clocking
needed to get the freq measurement done accurately.....

Whats the depth of grayscale ?

An LVDS link makes this pretty easy and robust, noise immune. There are
many good transceivers for this application.


Regards, Dana.
 
Last edited:

"SSTV" (slow scan TV) used to be a branch of
the ham radio hobby. I believe NTSC video was
all sent by FM (as there was a need to phase-lock
the sync & raster).

But that was analog video, not digital sent by FSK.
 

FM (audio tones) was the underlying mode for SSTV, that then handled by AM or SSB
transmission as the main carrier.

Frame rate was 6 s/ image up to and exceeding 100 secs.


Regards, Dana.
 

danadakk said:
Yes but its not a trivial design to get the filtering/tone detection right as the
speeds needed challenge the filter accuracy and stability needed. The clocking
needed to get the freq measurement done accurately.....

Whats the depth of grayscale ?

An LVDS link makes this pretty easy and robust, noise immune. There are
many good transceivers for this application.


Regards, Dana.
Click to expand...
You mentioned filtering/tone detection, is that determining the intensity of light at each pixel?
 

SSTV is intended to pass through audio circuits so it only requires a narrow bandwidth. Yes, the tone determines the video amplitude (brightness) with a specific tone being used to carry the sync pulses. Because it is an analog system, any tone could represent any video level within the bandwidth. FSK is more generally used in digital transmission where the tone is switched abruptly between two frequencies to represent digital '1' or '0' so it cannot be used for conveying analog signals unless they are encoded to digital format first.

You will find both analog and digital methods are difficult, but not impossible to achieve. Consider that you are sending 240 x 460 pixels per frame, that means 110,400 pixels per scan and at 15 FPS it means 1,560,000 pixels per second. Each of those pixels needs some kind of resolution to be able to recover a video level, for reasonable quality at least 8-bit (256 levels) are needed. Now consider that this is only for a monochrome image, you need to multiply by three to convey RGB or YUV if you want color.

You can see that to digitally modulate FSK you need several megabits per second rate. For analog FSK you have to shift and detect the carrier at several MHZ rate so the carrier needs to be several times higher than that and a wide bandwidth is needed.

Brian.
 


I see two reasonable methods to send "live video" (>= 15 FPS)
1. Classical analog video signal with single sideband AM
2. Digital video with MP4 encoding, different modulation methods can be used for the bitstream
 

Google "esp32 video streaming", more example projects.


Regards, Dana.
 

So what is the maximum baud rate frequency shift keying can have?
 

No principle limit, but practical limits, e.g. in terms of occupied bandwidth.
 

Old timey tone decoders used to need at least 10
cycles to make up their mind. Don't know what the
state of the art is today. But that sort of decision-
time would indicate an upper limit of 1/10 carrier
frequency (from which you'd probably back off
some, for reliability against noise and fading etc.).

If you're not hard over on FSK, I think phase (like BPSK)
detection may be quicker. If phase is stable then
the next edge is either in or out, per phase detector.
 

Can frequency shift keying have a baud rate of 100 megahertz?
 

Can frequency shift keying have a baud rate of 100 million bits per second?
 

Theoretically yes but an intractable problem at 100 Mhz due to filter
requirements I would think, accuracy, order/Q of filter, T and V effects.

Regards, Dana.
 

danadakk said:
Theoretically yes but an intractable problem at 100 Mhz due to filter
requirements I would think, accuracy, order/Q of filter, T and V effects.

Regards, Dana.
Click to expand...
What are t and v effects?
 

Temperature and Voltage.

Regards, Dana.
 

There is no theoretical limit to the number of bits per second in FSK but in practical terms, the faster the bit stream the harder it becomes to extract the bits afterwards. The problem is that to know which of the two frequencies the bit represents, it has to be found by detecting how many cycles of the frequency lie between the bit edges.

Example at low bit rate:
suppose a '0' (zero) is represented by 1KHz and a '1' is represented by 2KHz, your bit rate is 10 bits per second.
So one bit is 1/10 second.
If that bit was a zero, during the bit period there would be 100 cycles.
if that bit was a '1', during the bit period there would be 200 cycles.

Example at higher bit rate:
Same frequency but now at 1000 bits per second.
If that bit was a zero, during the bit period there would be 1 cycle.
if that bit was a '1', during the bit period there would be 2 cycles.

Even higher bit rate:
Same frequency but now at 1,000,000 bits per second
If that bit was a zero, during the bit period there would be 0.001 cycle.
if that bit was a '1', during the bit period there would be 0.002 cycles.

Detecting the difference between 100 and 200 is easy, it gets more difficult to tell when there is only 1 cycle difference and it becomes almost impossible when there is only 0.001 of a cycle difference. You can get around the problem by increasing the frequency so there are more cycles per bit but then then handling the frequency and timing the cycles becomes more problematic.

You question mentioned 100 Mb/s, if you make an assumption that it takes at least two cycles to make a reliable difference to measure you can see you are quickly heading towards Gigabit bandwidth and sub-nanosecond timing measurements.

Such things are possible but extremely difficult and expensive to implement, that's why FSK is not normally used at very high data rates.

Brian.
 

This might help -

**broken link removed**


Regards, Dana.
 

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