The proliferation of FPV drones has brought a flood of cheap wireless video tech. After flying and crashing a cheap FPV drone for a bit, [GreatScott] decided to try his hand at building his own video transmitter, which turned out to be a lot harder than expected.
While digital technology has caught up to the FPV world, a lot of systems still use analog video, especially for drone racing. The video quality isn’t great, but it has the advantage of very low latency. The technology is very similar to the old analog TV broadcasts, but mainly uses the 5.8 GHz license-free bands. It is essentially analog video signal, frequency modulated onto a 5.8 GHz carrier signal transmitted through an appropriately sized antenna.
After a brief failed experiment with a simple circuit built from discrete components, [GreatScott] turned his attention to voltage-controlled oscillators (VCO). He bought a couple of 5.8 GHz VCOs from Aliexpress, and created and used a simple opamp circuit to boost the FPV camera video signal to the required input level for the VCO. This failed to produce any identifiable image on his video receiver goggles. In an attempt to confirm that the VCOs produced the desired frequency, he ordered a similar 2.4 GHz VCOs and built a short range (20 cm) WiFi jammer. With a signal generator to create a simple input signal, and confirmed that it interfered with his laptop’s WiFi connection.
After more experimentation with other VCOs, the closest [GreatScott] came to success was a barely identifiable image transmitted using a Maxim 2.4 GHz VCO. If you have any ideas on what is missing in the VTX circuit, drop them in the comments below.
Building RF circuits that interfere with the legitimate signal around you, or broadcasting out of band, is generally not a great idea, and could earn you an unpleasant visit from the authorities. If you want to build your own digital video transmission, take a look at the Wifibroadcast project.
Last time I checked in on analog video it was Amplitude modulated. VCO sounds like voltage controlled frequency modulation. . . Audio was FM.
The C-band satellite TV signals were NTSC FM as well as the audio carriers. That’s why they had such good picture on a good TV.
Indeed. Actually analog video is modulated side banded to the right side of the carrier. The left side is suppressed. Audio was 4.5 Mhz higher in carrier frequency from the video carrier.
Vestigial Sideband
I went back to read the hobby king fine article.
One thing that has always peeved me off is when people are driving around staring at their phones. And then they get mad at me for smashing my horn when they almost hit me or someone else. Then they go right back to staring at their phone again… so i smash my horn again. There are various drop ship chinesium websites that will sell you various frequency jammers that are likely not legal without having a proper use case or exemption. But the thought has crossed my mind more than once of being able to smash a button and silently disconnect their phones rather than having my life and property put in peril. Makes me smile, but I would get in more legal trouble than they would for smashing into someone with their vehicle “on accident” when in fact their neglect and inability to focus on operating a machine is the real fault. In my experience, i have been in several accidents due to neglectful drivers and others not following proper use of the road, they get no legal penalty and I end up having to pay the cost due to the fact that insurance is a scam that never pays out without a more expensive lawyer. But then again for those people who are responsible, jamming would likely have them pick up their phone to look at it when their hands free call or podcast or music stops, potentially causing more havock than a single irresponsible driver.
Only tangentially related, but makes me think about every time someone wrecked my car or almost wrecked my car anytime i read about frequency interuption/jamming.
Also this:
https://m.youtube.com/watch?v=eDcNOLhZ2lc
The problem is that now most of these assholes are TEXTING instead of talking, which is harder to jam continuously (I think). And if you do, so what? They’ll just keep staring at the screen waiting for a reply (or keep typing, which doesn’t depend on reception anyway).
Never, under estimate, the predictability of stupidity. If you jam their signal. This will force the mobile user to demand a response from their mobile device, creating a digital dope fiend with banshee withdrawals episodes. Not to mention every user within range. Prepare to have your zombie kit on the ready. Be safe.
lmfao. This had crossed my mind.
You could say the same thing about people who smoke and drive or eat and drive
More anti-smoking bs
Most states have laws against distracted driving, particularly those driven by improperly used mobile devices. Forget the horn. That only antagonizes people, and some of these lunatics are even packing firearms. Report the vehicle description and license plate and dial 911. Do the same if you see speeding, reckless driving, etc. Pack a smartphone on a hands free holder and install a vehicle camera. Get these distracted lunatics off the road, and most states protect people who earnestly report distracted driving. Just my $.02.
The VCO tune input might not have enough modulation bandwidth. And even if it does, the frequency stability will be really poor. The higher the frequency the worse.
Not even the VCO tune input, but the slow op-amp used to buffer the video.
Also no pre-emphasis for the video signal or any kind of proper conditioning.
The main problem with tackling a project like this is that the pros use really expensive test equipment. This brave soul started at step 2. Step 1 is to build and/or buy cheap-but-effective test equipment. i got some hints from a super quick Google search that 5.8 GHz software defined radios do exist. What these do is “down-convert” the RF band you care about to a lower frequency that can be digitized by an affordable Analog-to-Digital converter. Software does the rest. Initially you don’t care about the decoding software (that comes later). Here, as you fiddle with your transmitter circuit, you want to visualize the frequency spectrum around your transmitter frequency. For example, to see how poor the frequency stability of your VCO is, and how much bandwidth is your transmitter occupying. With a spectrum analyzer, DIY or otherwise, you’ll learn a ton about RF modulation. Great for visual learners. Otherwise you are “flying blind.”
I’d recommend not building WiFi jammers or any WiFi transmitters that don’t comply with the standards or pass the radiated and conducted emissions tests. It takes a ton of really expensive test equipment to do this right and even though it may seem trivial, there are numerous life and property safety comms that are operating on these bands. It doesn’t have to be*intended* to be a jammer to be fined in the US, all it has to do is cause interference. I would definitely never associate my name or website with such a thing. There are numerous pipeline and oil and gas telemetry links (HART) FAA terminal radar, medical telemetry, etc., and the main characteristic of hobby projects that intentionally radiate signals without ever being measured for radiation signals (or for that matter ever really being designed) is they tend to have sometimes massive unintended radiation signals that the FCC will ask the local Ham radio or 2 way frequency coordinators to track down and identify so they can pull out their ticket book.
There are numerous ways to get video on WiFi bands that are totally fine, like using certified WiFi modules.
Seems like pointless handwringing to me. You’re assuming that what people build has remotely enough power to interfere with safety critical stuff operating in the ISM band near their home. Unless you live IN a hospital, this is not going to be an issue for 99.999% of people.
Thats what the guy thought who built a cellphone jammer, cuz peeps use there phones on highway. He put it in his trunk to jam them as he went down the highway to work
Unfortunately he also went by a tower knocking out service for a few min. Every morning .
( took diff route home) ..took 6 months before fcc caught him
The difference is that WiFi is in the ISM bands, which anyone and anything is allowed to transmit on (as long as the radiated power limit is not exceeded), while cellular networks are on their own licensed bands which only cell service providers and associated approved hardware is allowed to transmit on.
“As long as the radiated power is not exceeded”. Exactly.
Without putting it on a spectrum analyzer on a field site or anechoic chamber, how in the world can you say it radiates only in the ISM band or how much radiated power it has? And no, there *are* specific requirements for intentional radiators in the WiFi bands.Im not seeing any bandpass filters, etc. Actually the construction techniques are not suitable for RF in any case. Building proper transmitters is hard to do. I’ve done certification testing for a major power amplifier mfgr and it was always amazing to me what unexpected and unintended results happened from very minor things such as not bypassing a length of circuit board trace, etc.
Be sure to use the “unnecessary hand wringing defense” when talking to the guy from the field operations bureau.
Actually if you*do* encounter the FOB immediately admit it, hand them the device and promise to never do it again. They’re really nice guys until they’re not.
Not at all pointless hand wringing. Spot on. These bands are now chock full of devices that use channel hopping to get round the fact that the band is crowded. If you block the whole band with some POS home cooked tx they simply won’t work. If you get caught you will get at least a stiff fine, possibly worse. Remember that there are now medical devices that operate on Bluetooth.
The way they get you is they have (or at least had at the time I saw one) a really fancy Watkins Johnson receiver that scanned *all* frequencies looking for unusual frequency signatures. The one I saw was in an unmarked white van with a wideband discone antenna on the back.
Just sayin’….
A low power transmitter without a tuned antenna is unlikely to cause interference. (Yeah, yeah, the the NSA figures every piece of wire as acts like antenna.) The ISM band is *almost* a free-for-all. Every baby monitor interferes with your WiFi to some extent. That said, *no one* should be doing this sort of hobby work without at least a frequency counter to make sure they stay within the ISM and other legal RF bands. A downconverter (signal generator + mixer) is not impossible to build, but I’d recommend trolling Aliexpress for pre-built parts. Any circuit design in the GHz range will seem like black magic unless you have good simulation tools, an understanding of how to use them, excellent prototyping skills, and a network analyzer. Those used to start at $20k. A EE or physics degree is causally related to success in this arena. A solderless breadboard is not your friend.
P.S. I just checked, and Aliexpress sells all sorts of pre-built RF modules like frequency mixers and patch antennas. More to the point, they sell programmable PLL frequency synthesizers that go up to 6 GHz. I still recommend not embarking on a cobble-together-RF-modules project without some good way to measure the monster you have built. And definitely don’t hook up the patch antenna before you test your circuit on the bench. You can connect your Frankenstein transmitter to your off-the-shelf video receiver through coaxial cables (which will keep the FCC happy), but, if you’re not careful to add a signal attenuator in between, your problem is more likely to be too *much* power to the input of the receiver. Good luck.
Check modulation technique (AM or FM) and then Pre-Emphasis required
Analog video is amplitude modulation single side band folks. The reciever must also have the proper sideband filtering and look at the proper side of the carrier signal for the video information. Color information is transmitted on a subcarrier 3.579545 Mhz on the main carrier with the side band video information. Audio is 4.5 Mhz above the video carrier either on it’s own carrier signal or injected as a subbcarrer.
A radio frequency jammer (or rf jammer) prevents radio communications from contacting a receiver. There are 3 steps to making a radio frequency jammer. Step 1: construct the driver circuit. Step 2: build the flyback. Step 3: add the antenna.
what type and range of antenna is required for fm jammer circuit.also provide check list for this project
A device that is constructed, modified, or engineered to jam radio transmissions from reaching a receiver is known as a radio frequency jammer. Circuits that stop the improper use of flux and solder are long overdue in the world of electronics. Therefore, learning how to build a radio frequency jammer will often help you save time and stay safer.
I’m trying to create a broadband 5.8 GHz transmitter that will interfere with all channels and bands used by FPV drone video transmitters (VTx). This is to protect soldiers from kamikaze drones.
wow awesome