Boosting 5.8GHz 200mW FPV Transmitter to 2000mW: Circuit Diagrams and Legal Limits

Hello!

I am working on an FPV (first person view) helicopter project, and would like to extend the range of my transmitter that is on board of the thing for audio video feed.  it is a 200mW 5.8 gigahertz model.  I'd like to boost it as high as legally possible.. which I think would make it 2000mW.  Maybe someone has a good circuit diagram of this mod??  I know I could simply buy a bigger transmitter, but where's the fun in that??  I also want to know how I could potentially use the same technique on a wireless security camera, baby monitor, walky talkies, etc. 

Hope someone out there has wanted to do the same thing as me and either saved the schematic, or took some great pictures they can share!!  Thanks everyone!

(all comments are for the US/FCC, if you are in another country let us know and someone might be able to give you better information)

The limit for 5.8Ghz ISM spread-spectrum transmitters is 1000mW (significantly lower in some other countries). In order for the transmitter to be legal, it must be FCC part 15 approved and registered (and display the approval information on the device), or (this part is from memory) be one of up to 10 prototype transmitters constructed by you. These prototype transmitters must meet all FCC requirements for part 15 approval, but they do not actually have to be approved. Legally you cannot sell an unapproved transmitter in the US (with an apparent exception for engineering tools/devices which I have never found in the regulations). I suspect the FCC would take a very dim view on operating an unapproved transmitter as part of any ongoing commercial operation, regardless of whether it was part of the up to 10 prototypes exception.

That said, building a 5.8GHz amplifier is not an ideal introduction to RF circuit design and construction. At lower frequencies you can get away with constructing circuits an FR4 printed circuit boards and guesstimating the RF matching between components. The odds of getting good results at 5.8GHz are exceedingly low, and the chances that a 1W power amp would actually meet FCC regs without proper design and matching are even worse. Poor matching and PCB losses would also (most likely) put you well below the 1000mW design power output as every mistake results in power being lost or distortion being created.

There are off-the-shelf amplifiers available and FPV camera systems that operate at the legal limit. Note that many of these are not legal to operate in the US because they do not have FCC type approval, but selling them and using them appears to be common-place anyway.

Also, if you want to build something to improve FPV range, consider a tracking antenna on the receiver side with significant gain. A 17dbi tracking antenna is not that hard to build and would give your 200mW transmitter the same range as a standard 3dbi antenna with a 5000mW transmitter. This would also have the additional advantages of lower weight, power consumption and heat generation on the helicopter side (and cheaper replacement for the inevitable crashes during testing and development). You can track using GPS from a telemetry link, an IR beacon with optical tracker, etc etc. A 17dbi patch array can be built with (I think) a 40 degree beam width (-3db width) so the aiming is not that critical.

im gonna try that again.. and please.. keep in mind that this is the internet... you don't know who you are talking to.. so please don't assume you know anything about anyone else here!
I really really really shouldn't have to tell you this... but obviously I will since you had to post that ridiculous negativity rant you call "moderating".....
you should never assume that someone is not capable of completing something they have expressed intrigue about! If they aren't yet capable, perhaps now knowing what is before them, it will inspire them to work towards that plateau of achievement!

The simple fact that I posted such a question should indicate that I probably am qualified to do such a project, am willing to learn what I don't know, and already know that it's not going to be an economically wise project! If that was my concern, I would have asked you to point me to the cheapest piece of china amps you got!I

I won't even tell you what I do for a living, or what I do in my spare time, or what I have or have not achieved in my time on this earth. When it comes down to it... please don't discourage!!!! ENCOURAGE GREATNESS!! if someone is not yet qualified for such a project, ASSUME THAT THEY SOON WILL BE!!! BOOST THEM UP DONT BOOST THEM DOWN!!! If you must, remind people about the laws and regulations.. but please don't assume that the intention was to break those laws, or that those laws even exist wherever I happen to preside. Please, next time, simply mention the regulations, and proceed to encourage that person to read up on all the info you have about such antenna and rx and tx devices.. You obviously have some sort of knowledge on the subect.. and you have it in you to spread it to everyone! Why keep it bottled up???

Have yourself a great day.

Sorry if you felt my tone was in any way discouraging.

All of us have to read between the lines to know how to respond to posts like this. You asked for a circuit diagram. If I had simply provided one I would have been setting you up for failure.

Unlike digital and low speed analog circuits, RF design is a lot more than a schematic. The characteristics of the PCB traces and other interconnections form a critical part of the eventual design, and at very high frequencies (like 5.8GHz) these affects make the changes of an amplified designed and implemented by an experienced RF engineer well under 100%. In order to test such an amplified and verify that it meets the requirements to operate legally you would need to make a significant investment in test equipment (minimum a calibrated power meter and spectrum analyzer, unless you are really lucky that is >$5K for used equipment still in calibration).

You didn't specify whether this was a hobby project or part of the development of a commercial product, so I provided an overview of concerns for both.

In the last paragraph, I provided what I would do (and have done) in your shoes. Increasing transmitter power is probably the wrong solution to your actual problem (as I understand it) which is FPV range. Increasing antenna gain on the receiver side is a much better solution. I use three antennas with an RSSI based video switch (three receivers). One omni antenna for short range where tracking accurately is difficult. One patch panel for medium range (about 40 degree beamwidth) and one dish for long range (1 degree beam width). Both the patch panel and dish track the UAV using GPS on a separate telemetry link. As I have an amateur radio license I can use a lower frequency transmitter for the telemetry link (which is also a failsafe control link) which can operate at ranges beyond what the dish link can for FPV. 5.8GHz is line of site regardless of transmitter power or antenna gain and the UAV is programmed to return back along the recent path if the telemetry link is lost or if the FPV video link is lost.

With an amateur radio license I am allowed to use >1000mW for the FPV link, but choose to use 400mW because using high gain receiving antennas makes more sense.

So, I am "boosting you up" by giving you useful (and field proven) advice.

If you are really set on using or building a 5.8Ghz amplifier, take a look at mini-circuits (www.minicircuits.com) for both pre-built amplifiers and components complete with datasheets and circuit diagrams. Even if you want to build using the components, download the datasheets for the completed amplifiers, they usually include schematics and performance information getting you pointed in the right direction.

i pretty much just read the last paragraph in which you actually provided the information requested. like I said.. leave it to the person asking for such info to decide if they are capable of such a project! Does it make a difference weather I can or cannot do it>?? It does not. I requested the information because I am obviously investigating that for myself! And since I asked such a specific question, it would indicate that I have gotten to the point in my research where I feel I am ready to peruse a previously built, tried and true design and schematic. It's what everyone does when they are curious about building something themselves! I researched building a nuclear weapon in the same way as if I was actually going to do it.. just because I was curious about what it would actually take! there is no way I would ever actually want to, or have the funds or the means to actually accomplish such a feat! It did not stop me from researching it from the perspective of an actual design engineer given the task of putting one together.

With that being said... I do intend to actually put this together! I do have or have access to the necessary equipment. I have a formal education in mathematics, physics, electrical technician diploma, and topped off with a few chemistry courses and computer science randomly scattered about. Schooling has been done for many years now for me, and I have learnt many multiples of what I learnt formally in uni and college from my own research and experimenting since such time!

I am currently, and most likely permanently, unemployed by choice. I have no intentions of commercial development of anything I work on. If I discover anything useful, it will hopefully be in the public realm because of me before anyone gets their private patent on it. I think the ordeal of the patent process followed by developing a business around such a thing would completely drain me from the fun of the discovery in the first place! I do not wish to bog myself down with such fantasies... because that is really what they are for the majority of inventors! The pursuit of material wealth is not something that I concern myself with. If you stop and think about it and look around, you probably already have more than enough of everything you need to survive and thrive and be completely content with your life. I realized after years of taking jobs that successively paid more and more, that when the job would come to an end, I would always end right back up where i had been before taking the job in the first place.... no more in the bank, no more in my wallet, smile on my face smaller than previously if any change at all. So why go thru all that in the first place if it gets me no resolve? I'd rather use my energy, my life force, my energy of life, towards my own goals, my own inspirations, my own whatever I want! not towards some entity labled as a corporation that is merely a fictional rendering of someone elses fantasy!

If you claim to have done the research, why did you use the word think when discussing the power requirements. I believe you are being unnecessarily over sensitive in dealing with the replies, it would have made more sense if you had stated some of your background earlier rather than later. Dean is correct, in these forums you can never tell at what level people are working at,
cheers,
Richard

my point was that my background shouldnt matter. if i was a highschool student and i asked if anyone had done this before and had a schematic.. i dont think its required to disclose all that crap so then you can weigh in your mind if i'm up to the task or not when you really don't have a clue what my capabilities are, or anyone elses for that matter. Its just a really limiting way of dealing with a subject such as diy.. its limiting by nature, because you are only asking my background in order to decide how much info and what caliber of info I can handle, or anyone ur talking to could handle or comprehend. The fact of the matter is, if its a diy type person, if they can't handle or can't comprehend the info ur layin down, then they will either realize right then and there that they are over their heads, and may ask for an alternative at that point, or B.. they will examine the proceedure or method or whatever and absorb it into their brains... then pick it apart and dissolve the problem into its fundamental issues.. after meticulously attacking any issue, no matter what complexity, and no matter how foreign the concepts, anyone can learn to do anything anyone else can... in a relatively short period of time. That's the beautiful thing about our present information age... information is more accessible than ever, and soon enough people are going to realize that specialized educations are a thing of the past... because everyone will realize that they can do anything they set their browser to!

only if they practice, and get good at it... like i tend to think i have.. but am always evolving my methods. just as i hope others are aswell ... so i hate to think they are being limited based on what someone else thinks they can handle!