Decoding Analog RF TV signals and using FPGA to process them.

Thread Starter

nondem

Joined Nov 19, 2021
3
I'd like to build some type of device to take the signal from the RF out (Analog TV Channel 2-3) on some of my 8-bit computers and split out the audio and video signal for use on HDMI or VGA+Audio. I know there are devices/TVs can still tune Analog but they generally have a hard time staying tuned into the signals these antiques produce. With some exceptions LCD and other tuners constantly try to auto-tune w/o ever locking.
Of course there are mods that can be done inside the computers to get composite video but I don't want to modify these increasingly rare machines. Not to mention getting Audio often involves even more mods.
I've got experience w/Arduino and ESP32 microcontrollers and basic electronics. I'm in the early stages of tackling FPGA's but I'm thinking this might be a good project learn with. I do have FPGA Dev boards with VGA and HDMI outputs on them already.
My assumption is I may be able to put together some type of Analog circuit to capture the signal and connect that to a FPGA for processing to get output in VGA or possibly HDMI. Does anyone have some ideas on where to start or how something like this could be made to work?
 

ronsimpson

Joined Oct 7, 2019
2,005
The output is HDMI or VGA. That is all ready on your FPGA board.
Input is?? TV Channel 2-3? Where are you getting Analog 2 from?
 

crutschow

Joined Mar 14, 2008
29,492
I do have FPGA Dev boards with VGA and HDMI outputs on them already.
What inputs do these boards require to generate the video outputs?
Or are those inputs, not outputs?
You would likely need to generate a digital signal from the analog signal using a high speed A/D converter to do any digital processing.
 

Thread Starter

nondem

Joined Nov 19, 2021
3
Thanks for the replies...one board I have has HDMI out(Arduino Vidor 4000) and the other has a VGA out plug(Go Board). They are both entry-level dev boards to learn on obviously. As I mentioned I understand I'll need some type of front end to get the Analog signal into the FPGA but the outputs are already prewired. The output from the 8 bit computer is just an RCA plug that would go into a switchbox that converts it to a 300ohm twinlead or 75ohm coax. There are converter boxes that do exactly what I want but I've not found one that "likes" the broadcast tv signal from an 8 bit computer.
 
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ronsimpson

Joined Oct 7, 2019
2,005
Getting from Channel 2 to digital in a FPGA is hard.
I have done analog video to FPGA and will never do it again, partly because it is "old school" out dated.
Find a easy FPGA project. Make a video game that outputs on a HDMI monitor or TV.
 

ronsimpson

Joined Oct 7, 2019
2,005
.at least I've learned this isn't a beginner project
Channel 2 is at 54-60mhz, Channel 3 = 66-72mhz, ................................
Amplify, filter,
All channels are "beat down" to 41.25MHz for audio (FM) and 45.75MHz for video (AM)
The audio is processed much like a mono-fm radio would.
The video is processed much like a am-radio (for B&W) video.
The color is linked to a 3.579545 MHz Color Burst frequency.
Every scan line a short burst of 3.579545 MHz is sent and the receiver must lock to the frequency and not stray away for a long time.
1637422427184.png
Analog Video:
1637422824636.png
Color: If there is no color burst to lock to then any signal above "black level" is "B&W" (gray).
If the signal has color then where the signal sits with respect to the phase of 3.579545 MHz determines its color.
A B&W "dot" sits on the screen. Its brightness is how high it sits in the above picture. In a color set each dot is a small rainbow and where the "dot" sits (in time left to right) determines its color. There is some math to get RGB out of phase shift.

That is a very simplified description. Probably some errors. lol
RonSimpson
 
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