I tried Wireless Video but ended up building a WiFi Jammer (A Fail Story)
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Date: 2022-08-08
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Comments and reviews: 14
Thomas
Unfortunately there are a lot of mistakes in this video, which is not to say the video is bad or that it is all your fault, I just want to point that out and provide useful feedback. In my opinion the biggest mistake is that you are taking for granted that for every frequency you can use the classical lumped model of the components. This is unfortunately not the case. Every component has parasitic resistance, inductance and capacitance and this must be taken into account in the design of high frequency electronics. Just the fact that you are not using a PCB, but THT components with immensely long leads is a big problem. You also removed the shields from the VCOs, which likely causes quite a lot problems. At such high frequencies you have to work with PCBs and/or waveguides and take in considerations every single aspect of the circuit. Maxwell's laws are unforgiving.
I really hope you find this useful and constructive. If you have any question feel free to get in touch!
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Unfortunately there are a lot of mistakes in this video, which is not to say the video is bad or that it is all your fault, I just want to point that out and provide useful feedback. In my opinion the biggest mistake is that you are taking for granted that for every frequency you can use the classical lumped model of the components. This is unfortunately not the case. Every component has parasitic resistance, inductance and capacitance and this must be taken into account in the design of high frequency electronics. Just the fact that you are not using a PCB, but THT components with immensely long leads is a big problem. You also removed the shields from the VCOs, which likely causes quite a lot problems. At such high frequencies you have to work with PCBs and/or waveguides and take in considerations every single aspect of the circuit. Maxwell's laws are unforgiving.
I really hope you find this useful and constructive. If you have any question feel free to get in touch!
reply
ats89117
You are looking at the wrong end of the horse. Instead of trying to boost the transmit power, you should focus on building a lower noise receiver. FM receivers make use of a principle known as FM improvement which allows trading off bandwidth for improvement of the signal to noise ratio in the information band. This works great at high carrier to noise ratios, but breaks down at a threshold level which is determined by the modulation index and the type of detector. The breakdown occurs when cycle skipping errors start to occur, and at carrier to noise ratios below threshold, the quality of the signal rapidly deteriorates. Without going too far into the weeds, it's a given that the receiver in your goggles isn't great, and it should be possible to improve it to allow significant improvements in range. An alternative would be to improve the receive antenna by making it more directional.
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You are looking at the wrong end of the horse. Instead of trying to boost the transmit power, you should focus on building a lower noise receiver. FM receivers make use of a principle known as FM improvement which allows trading off bandwidth for improvement of the signal to noise ratio in the information band. This works great at high carrier to noise ratios, but breaks down at a threshold level which is determined by the modulation index and the type of detector. The breakdown occurs when cycle skipping errors start to occur, and at carrier to noise ratios below threshold, the quality of the signal rapidly deteriorates. Without going too far into the weeds, it's a given that the receiver in your goggles isn't great, and it should be possible to improve it to allow significant improvements in range. An alternative would be to improve the receive antenna by making it more directional.
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SeanBZA
As well the modulation is negative video, in that your video signal is inverted, with the bottom of the sync voltage being 5V, and the brightest point being 2V, so the modulation will be recovered properly. This is done in broadcast video so any impulse noise, like RF arcing and lightning, will tend to drive the demodulated signal to the black sync level, not full white, so it is less objectionable in the picture, having a screen go black is easier for the sync circuitry to recover from, than trying to restore the DC levels after going full white. Single 2N2222 as inverting common emitter amplifier with a gain of 2 will do this, just bias it so the bottom of the sync pulse, AC coupled into the base with a 100uF capacitor, will just turn the transistor off, and then your front and back porch, along with the colour burst, should sit around 4V off ground, video peak taking it to 2V.
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As well the modulation is negative video, in that your video signal is inverted, with the bottom of the sync voltage being 5V, and the brightest point being 2V, so the modulation will be recovered properly. This is done in broadcast video so any impulse noise, like RF arcing and lightning, will tend to drive the demodulated signal to the black sync level, not full white, so it is less objectionable in the picture, having a screen go black is easier for the sync circuitry to recover from, than trying to restore the DC levels after going full white. Single 2N2222 as inverting common emitter amplifier with a gain of 2 will do this, just bias it so the bottom of the sync pulse, AC coupled into the base with a 100uF capacitor, will just turn the transistor off, and then your front and back porch, along with the colour burst, should sit around 4V off ground, video peak taking it to 2V.
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technic
The reason why you only got a sort of camera signal from any VCO you have tried was that analog terestrial TV signal has its video signal AM modulated and the audio FM modulated, the old analog satellite TV was FM FM (FM video, FM audio) the reason why the image was sort of there was because you most likely used slope detection without even knowing it, FM slope detection uses AM demodulator tuned to the edge of the FM signal to demodulate it, it works ok-ish for audio but since a composite video signal is so wide in bandwidth, it has no chance. So the key word is AM modulated video signal. And as someone already said, the 7 marking on the TV was most likely just a marking for the dial scale, since you had your TV set to VHF low band, you were tuning somewhere between 54 and 88Mhz.
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The reason why you only got a sort of camera signal from any VCO you have tried was that analog terestrial TV signal has its video signal AM modulated and the audio FM modulated, the old analog satellite TV was FM FM (FM video, FM audio) the reason why the image was sort of there was because you most likely used slope detection without even knowing it, FM slope detection uses AM demodulator tuned to the edge of the FM signal to demodulate it, it works ok-ish for audio but since a composite video signal is so wide in bandwidth, it has no chance. So the key word is AM modulated video signal. And as someone already said, the 7 marking on the TV was most likely just a marking for the dial scale, since you had your TV set to VHF low band, you were tuning somewhere between 54 and 88Mhz.
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aduedc
I think you should divide the task in several parts, and work on each part. Also, you should use real PCB instead of wire bonding parts, to reduce the noise.
Here How I divide the task.
Camera output -> A2D -> Packetize your digital data and add Forward Error Correction (FEC) ->I-Q Modulator -> Transmitter -> Transmit Antenna -> Receive Antenna ->Receiver -> I-Q de-modulator de-Packetize your digital data and correct the packet errors --> D2A -> Monitor
The way you currently doing things, I think you are corrupting your signal before you even sending the signal to transmitter.
Use Coax cable and microstrip lines and correct terminating resistor to protect the analog signal that you are getting out of you camera.
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I think you should divide the task in several parts, and work on each part. Also, you should use real PCB instead of wire bonding parts, to reduce the noise.
Here How I divide the task.
Camera output -> A2D -> Packetize your digital data and add Forward Error Correction (FEC) ->I-Q Modulator -> Transmitter -> Transmit Antenna -> Receive Antenna ->Receiver -> I-Q de-modulator de-Packetize your digital data and correct the packet errors --> D2A -> Monitor
The way you currently doing things, I think you are corrupting your signal before you even sending the signal to transmitter.
Use Coax cable and microstrip lines and correct terminating resistor to protect the analog signal that you are getting out of you camera.
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MC's
First of all, welcome to the FPV world, dude!
I do FPV even with rc cars! There are cheap cameras with transmitters in the market and I just stick them with double sided tape to my cars.
Either way, analog FPV doesn't have a very good penetration, but you can get LOTS of range. There are people who flies over 30km! The issue is the EU regulations, you guys are stuck to 25mW. Which doesn't help much.
But there are video transmitters that go up to 1. 6W, perhaps even more!
Oh, now there are 3 different HD FPV systems as well. But they're really expensive, so I stick to analog.
Anyway, fantastic video as always!
Stay safe and flying (and creative) there!
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First of all, welcome to the FPV world, dude!
I do FPV even with rc cars! There are cheap cameras with transmitters in the market and I just stick them with double sided tape to my cars.
Either way, analog FPV doesn't have a very good penetration, but you can get LOTS of range. There are people who flies over 30km! The issue is the EU regulations, you guys are stuck to 25mW. Which doesn't help much.
But there are video transmitters that go up to 1. 6W, perhaps even more!
Oh, now there are 3 different HD FPV systems as well. But they're really expensive, so I stick to analog.
Anyway, fantastic video as always!
Stay safe and flying (and creative) there!
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Kai
Is the op amp that you use suitable for 5. 8 GHz? Most aren't. Also, with this high frequency, it would be better to use smd components. The feet of THT ones have a not to be underestimated inductance at this frequency. You also have to consider Impedance matching in your circuit! It would be best to design a quick PCB with the right impedance and components suitable for 5. 8 GHz. Also, the simplest way of improving the range would be to use a higher gain Antenna. (But be aware, that this increases the directionality of your signal. Meaning, if you turn to much to the right or left you can loose the signal.
Regards an RF engineering Student: D
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Is the op amp that you use suitable for 5. 8 GHz? Most aren't. Also, with this high frequency, it would be better to use smd components. The feet of THT ones have a not to be underestimated inductance at this frequency. You also have to consider Impedance matching in your circuit! It would be best to design a quick PCB with the right impedance and components suitable for 5. 8 GHz. Also, the simplest way of improving the range would be to use a higher gain Antenna. (But be aware, that this increases the directionality of your signal. Meaning, if you turn to much to the right or left you can loose the signal.
Regards an RF engineering Student: D
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Kim
So from my experience this single transistor circuit from internet does not work, my approach was that i just took +/- 500Mhz sine generator circuit based on collpits oscillator and 2sc3356 transistor from my other project and mixed camera signal to antena output through some lcr filters, i can mail approximate schematic of my project if you want, i managed to get around 50m open air transmission without any problem and with no amplification stage (also 2sc3356 is pretty good choice for such projects, it is smd npn with frequency of 7Ghz and little noise)
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So from my experience this single transistor circuit from internet does not work, my approach was that i just took +/- 500Mhz sine generator circuit based on collpits oscillator and 2sc3356 transistor from my other project and mixed camera signal to antena output through some lcr filters, i can mail approximate schematic of my project if you want, i managed to get around 50m open air transmission without any problem and with no amplification stage (also 2sc3356 is pretty good choice for such projects, it is smd npn with frequency of 7Ghz and little noise)
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Kau
To test if RF equipment works one needs a spectrum analyser. That way you can observe your carrier signal at 5. 8GHz. With the video signal, it may be important to see what modulation index is used for the transmitting signal, that way you can emulate it accurately using the amplifier circuit. Also, the bandwidth of the transmitting signal is important for an FM signal.
However, great video, it's great to show that in electronics one doesn't always know how to do things. This is inspiring to us aspiring engineering.
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To test if RF equipment works one needs a spectrum analyser. That way you can observe your carrier signal at 5. 8GHz. With the video signal, it may be important to see what modulation index is used for the transmitting signal, that way you can emulate it accurately using the amplifier circuit. Also, the bandwidth of the transmitting signal is important for an FM signal.
However, great video, it's great to show that in electronics one doesn't always know how to do things. This is inspiring to us aspiring engineering.
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Paul
Greatscott, it's a good educational video. But I can help you a little further. If you want to amplify an NTSC, SECAM or PAL signal make sure the sync level is maintained (both amplitude and pulse width. The sync level should always be zero volts (which I didn't see at 7: 58. Keep in mind that a video signal needs a bandwidth of 5MHz. Make sure you have linear amplification over the full bandwidth. I also recommend using DC amplification and not AC amplification (capacitor) for your video signal.
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Greatscott, it's a good educational video. But I can help you a little further. If you want to amplify an NTSC, SECAM or PAL signal make sure the sync level is maintained (both amplitude and pulse width. The sync level should always be zero volts (which I didn't see at 7: 58. Keep in mind that a video signal needs a bandwidth of 5MHz. Make sure you have linear amplification over the full bandwidth. I also recommend using DC amplification and not AC amplification (capacitor) for your video signal.
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Dave
I think it's your opamp. If I read it correctly it's an MCP602, which has a pretty steep gain falloff after 1-2mhz, and a unity gain bandwidth of 2. 8mhz. Composite signals can swing much faster than this. You should try looking at the pre and post amplification signals a little closer on the scope, look for ringing etc, and also pay attention to the size of the loops of wire you're creating in your free-air circuit. I'm looking forward to another wireless video. video! Keep up the awesome work!
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I think it's your opamp. If I read it correctly it's an MCP602, which has a pretty steep gain falloff after 1-2mhz, and a unity gain bandwidth of 2. 8mhz. Composite signals can swing much faster than this. You should try looking at the pre and post amplification signals a little closer on the scope, look for ringing etc, and also pay attention to the size of the loops of wire you're creating in your free-air circuit. I'm looking forward to another wireless video. video! Keep up the awesome work!
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Gurux13
Setting aside why it didn't work - I think other commenters left lots of tips, I'd recommend getting an SDR to see what's actually being transmitted. RTL-SDR wouldn't quite cut it, but there are other products: )
Also I'm quite uncomfortable with anything above 100Mhz as basically everything becomes antennae, and parastitic capacitances and inductances eat up a lot of useful power. It might be that assembling it in midair caused some losses like that.
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Setting aside why it didn't work - I think other commenters left lots of tips, I'd recommend getting an SDR to see what's actually being transmitted. RTL-SDR wouldn't quite cut it, but there are other products: )
Also I'm quite uncomfortable with anything above 100Mhz as basically everything becomes antennae, and parastitic capacitances and inductances eat up a lot of useful power. It might be that assembling it in midair caused some losses like that.
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CandyGramForMongo
Filters and boosters! While I have no experience or knowledge, my first thought is that some of the signal components are more important than others. So boost those signals before transmitting and filter back to normal on the receiver. Think of it like Dolby. Don t like hiss? Double the boost of the music that shares the range with hiss, then halve it on playback. Boom, half the hiss, noise reduced!
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Filters and boosters! While I have no experience or knowledge, my first thought is that some of the signal components are more important than others. So boost those signals before transmitting and filter back to normal on the receiver. Think of it like Dolby. Don t like hiss? Double the boost of the music that shares the range with hiss, then halve it on playback. Boom, half the hiss, noise reduced!
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Talis
Should have mentioned that messing around with RF transmitters like this can get you in trouble. Should get at least amateur radio license before you start messing around with transmission. Even using radios that are not meant to be used in your country/region can be harmful, it is very tightly regulated. The knowledge required to get a amateur radio license would go a long way in helping what went wrong here.
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Should have mentioned that messing around with RF transmitters like this can get you in trouble. Should get at least amateur radio license before you start messing around with transmission. Even using radios that are not meant to be used in your country/region can be harmful, it is very tightly regulated. The knowledge required to get a amateur radio license would go a long way in helping what went wrong here.
reply
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