Choosing Your FPV Video Transmitter Frequency & Power
There are two main factors when deciding on your video transmitter and that is the frequency you transmit on and the output power level.
FPV Video Transmitter Frequency
There are basically four different frequency bands used in FPV analog video transmission:
- 900 MHz
- 1.2 & 1.3GHz
- 2.3 & 2.4 GHz
The lower the frequency the better the signal can penetrate through objects so if your goal is to fly behind large stands of trees, buildings, or hills; getting a 900MHz may be the best bet. The issue with lower frequencies is the antennas have to be larger so if space and portability are a concern, then you will be better served with higher frequencies and stick to line of sight flight (oh, if it were only that simple).
Next factor to take into account is what frequency your radio system operates on. I think it's a safe bet to say the majority of people reading this are running on 2.4GHz radio systems so that is the example I will use here, but the same principles apply when choosing an FPV video frequency with any radio system frequency.
So, if you fly with a 2.4 GHz radio, you can scratch 2.4 & 2.3 off your list. You can also scratch 1.2 off - why? Well, 1.2 x 2 = 2.4 and it's possible to get a 1.2GHz harmonic resonating at 2.4GHz. All of a sudden our list has been cut in half and we are left with 900 MHz, 1.3GHz, and 5.8GHz.
If you have a GPS antenna on-board your FPV RC aircraft, you can now throw 1.3GHz out of the race as well. GPS operates at 1.5GHz and 1.3GHz so with a nice video transmitter and antenna screeching out in the same or close to band, your GPS signal could and likely will get partially knocked out.
This leaves you with two choices, 900 and 5800MHz (same thing as 5.8GHz). Remember, 900MHz needs big antennas and in most areas also requires a radio operators licence to use legally; which is incidentally something you should check into no matter what frequency you transmit on as many countries have strict regulations on what frequencies and power levels you can lawfully use either with or without a special amateur's radio operating license. The other issues with 900MHz is the video transmission image quality is not as good and there can be many other noise sources transmitting near this frequency such as cell networks so the lower frequency bands are more likely to experience noise and interference issues.
Leaving us with good old 5.8GHz. This in my opinion (at least if you fly with a 2.4GHz radio system and have GPS on board your aircraft) is the best all round choice for your first attempt at FPV. Yep, it's what frequency I also chose for all the above reasons not to mention the Fat Shark Dominator video goggles I use came with a built in 5.8GHz receiver option keeping my ground station as simple, small, light, and transportable as possible. 5.8GHz is out of most other transmitting frequencies so it tends to also be the "quietest" and usually provides the best quality video signal.
5.8GHz antennas are also smallest of the bunch so that saves not only space, but a little money as well. The only real issue with 5.8 is it has next to no penetration ability, meaning even flying behind a tree or shrub can mess the image up. It's also not great for long range flying because high frequency wave energy is absorbed in the air by humidity or other atmospheric particulates much easier than lower frequency waves. Again for a FPV beginner, 5.8GHz is generally the best overall match due to it's simplicity and lack of conflict with other frequencies.
All that said, if you fly on another radio frequency (perhaps an older 72 or 35 MHz radio), using a 2.4 GHz video transmitter is a great all round choice. Speaking of older analog 72 & 35 MHz PPM radios; they are wonderful for FPV aircraft giving improved control range! So if you have one kicking around or find one on eBay really cheap, most medium distance FPV'ers highly recommend them.
FPV Video Transmitter Power
Next up is the power of the FPV video transmitter. This will be listed in mW and the golden beginner power rule here is never go more than about 500 to 600 mW maximum. That's huge amounts of transmit power for FPV and with good directional antennas can take you well past 20 km even on 5.8 GHz!
You'll never need to go higher than that power level and many people fly at much lower power levels (250mW for example) without issue. Yes, there are certainly some 1 and 2 Watt FPV transmitters out there but all they will do while screaming away is likely take out your radio or GPS reception & drain your battery down quicker.Good antennas give you improved range in this FPV game, not more powerful transmitters.
FPV Video Transmitter Channels
The large majority of FPV video transmitters also allow you to choose between several different transmit channels within the specific frequency band. For example, that Immersion 5.8GHz transmitter I use has seven different channel selections (5.740, 5.760, 5.780, 5.800, 5.820, 5.840, 5.860GHz). This allows you to "fine tune" your setup for the best image transmission if one channel for example seems a little nosier than the others (provided of course your ground station receiver also has the ability to receive the same multiple channels within the band). Keep that in mind! Not all TX & RX systems (even if they are in the same bands) transmit on the same exact channels. For example Immersion RC works with Fat Shark's channels. Channels are listed in the specs of both TX and RX's so just have a peek at the specifications to make sure your transmitter is compatible with your receiver channels.
FPV Video Transmitter RF Connection Type
Lastly, I should make mention of one other little item to be aware of with FPV video transmitters and that is the type of RF antenna connection they use.
The vast majority of FPV video transmitters, receivers, and antennas use SMA (sub miniature version A) thread on coaxial RF connectors.
Just keep this in the back of your head when looking at the component specifications in case you happen to get an oddball transmitter that doesn't use the standard SMA, but the antenna you plan on using with it does. If that's the case you'll have to get the correct coaxial adapter.
Transmission/antenna warning... No matter what transmitter or antenna you use, never-never turn your video transmitter on without the antenna attached.This will quickly burn out the video transmitter if it's not allowed to radiate the RF energy out through the antenna.
Don't overlook the importance of these components in your system
Most start using what comes with most video transmitters and receivers - a simple omni directional linear polarized whip antenna set which, depending on your frequency, can give very poor performance.Choosing FPV antennas is generally the last thing newbie first person view pilots think about.
If you use 5.8GHz, these simple linear antennas are so bad (because high frequency 5.8GHz bounces off stuff so easily causing multi-path interference), I don't even know why they include them with 5.8 GHz video transmitters and receivers? This is really unfortunate because as I mentioned on the FPV RC page, your antennas are the components that will have the largest single impact on your video transmission quality and range so take a little time here to choose the correct one/s.
There are essentially 4 main PFV antenna choices you have and you may need to use a different one on your aircraft video transmitter from what you use on your ground station video receiver depending on your specific needs.
- Linear Polarized Omni Directional Antenna
- Linear Polarized Directional Antenna
- Circular Polarized Omni Directional Antenna
- Circular Polarized Directional Antenna
Choosing FPV Antenna Frequency
The other FPV antenna choice option I have not mentioned yet (because it's really not a choice at all) is you have to get the correct FPV antenna set for your specific video transmitter & receiver frequency. You can't use a 2.4GHz antenna set for example on a 5.8GHz system. Antennas are specifically "tuned" to each frequency so when you go FPV antenna shopping, make sure you get the correct frequency antennas for your system.
The higher the frequency, the smaller the antennas get so if you want to keep things nice and portable, stick with higher frequencies.
FPV Transmitter Antenna Placement
Where you place your transmitter antenna on-board your FPV aircraft is another important consideration for getting the best range and video signal. This will generally require a little experimentation on your part. Another golden rule here to start with is to keep your video transmitter antenna as far away from your radio system receiver antenna/s and GPS receiver antenna (if you use GPS) as possible.
The next thing to think about is the actual antenna placement position/orientation on the aircraft. For example, when I first started out, I had my video TX cloverleaf sticking up above the F550's top plate.
This seemed to work fine until I started getting further and further away. In this position I was only getting about 800 meters away and only 200 meters high. Sometimes even less and when I turned around to fly back home the first time, I completely lost the video image. I could only get it back by turning back around so the rear of the F550 was facing my position and had to fly home backwards a fair distance (another advantage of a multi-rotor I suppose).
As it turned out, in that upright position, the main body of the hex rotor was partially shielding the video RF from getting back to my receiver antenna. When I turned around to come home, the antenna was completely shielded by the body and I lost the image completely & immediately.
The fix was super simple, I just rotated the antenna to hang below the aircraft and have had super clear video since. So just doing that simple little antenna move, more than doubled my video transmit range.
One other item to be aware of with these antennas is they have "null" zones where the signal drops off sharply. On the circular polarized lobe type antennas, that null zone is directly above and below the antenna (assuming the antennas are positioned vertically as recommended). You will notice this the first time you fly more or less directly overhead as the image starts breaking up and then clears right up after you pass by. The fix is easy, don't fly directly overhead
FPV Antenna Conclusion
To Sum Up Your FPV antenna decision making process as simply as possible.
- Pick your polarization type (likely circular).
- Pick your direction. Always omni for the aircraft; omni or directional for your ground station. Again I recommend beginners stick with omni directional for the ground station as well when first starting out. It's easy and inexpensive to get a directional later on if you want improved video range.
- Ensure you get the right frequency antenna set for your FPV system (ie. 5.8GHz antenna set for 5.8GHz video transmitter & receiver).