When it comes to choosing a video transmitter (VTX) for mini quad, the factors you need to consider shift from long range and high power to small size and bandwidth friendly. In this article we will discuss all the factors on how to choose VTX for a quadcopter.
In my Early RC flying career I flew larger 450+ sized multirotors, where power, space and lift were virtually limitless. But with these newer, smaller racing mini quad every gram shaved pays off in flight performance. Not to mention I could be flying with multiple pilots at the same time so power and channels are also a big consideration.
Index of Content
- What is VTX
- Image Quality and VTX
- Analog and Digital FPV system
- Signal Quality and VTX
- Considerations in choosing VTX for mini quad
- Output Power and Range
- How easy it is to change channel
- Antenna connector
- Input Voltage and Output Voltage
- Internal Microphone
- Support for SmartAudio / Telemetry
- How to use VTX properly
- Recommendation for the best mini quad VTX
What is VTX
VTX stands for video transmitter, it’s an essential part of a FPV system. It’s a device that sends the video from FPV camera to a video receiver, which can then display it on a monitor or FPV Goggles.
VTX can use many different frequencies, such as 1.2Ghz, 2.4Ghz etc. But the most popular frequency used in mini quad is 5.8Ghz because:
- Antenna can be made smaller
- 5.8Ghz are legal in many countries
Image Quality and VTX
When it comes to quality of the footage, such as colour, contrast, wide dynamic range, sharpness etc, these have very little to do with your VTX but your FPV camera. So paying extra money for a high end VTX isn’t going to dramatically improve your image quality.
Digital and Analog FPV systems
The 5.8Ghz system we use for FPV are some old analogue technology, so don’t expect any HD level video. The HD video you see on Youtube, are captured with an HD action camera.
There is digital solution for FPV now for mini quad FPV flying that offers much clearer image, such as the Connex Prosight.
However since the technology is still new, they are quite expensive and bulky. They are not quite as good as the footage from a HD action camera, but still they are much better than analog. In this guide we will focus on the good old 5.8Ghz analog VTX, if you are interested in the Prosight make sure to check out our review.
Signal Quality and VTX
When it comes to signal quality, generally the FPV antenna and receiver play a bigger part than VTX. For example using a diversity receiver (dual antennas) is going to help reduce of the chance of losing signal, and using higher gain antennas can give you longer range.
So why are we paying good money for a VTX really? Keep reading…
What to look for when choosing VTX for Mini Quad
Analogue video quality is not attractive at all comparing to HD. Even in the best condition, the image is blurry, low in resolution and noisy compared to your GoPro footage. The reason we are still using it today is because of the compact size, extremely low latency, low price and availability.
With mini quad getting more popular, VTX are made smaller and lighter. Size and weight are pretty much similar these days between modern VTX’s, so we won’t discuss it in detail here.
When choosing NTSC/PAL quality 5.8 GHz VTX for mini quad, there are also some other factors to consider apart from weight and size.
Power and Range
The VTX output power determines how much power is radiated from the transmitter. Generally speaking the more power means more range.
Mini Quad VTX can have different power levels, for example 25mW, 200mW and 600mW are the common ones. Some more advanced VTX’s are switchable between different power levels.
The output power of your transmitter is the total amount of radio energy your antenna will be delivering to receiver. Both the VTX power and antenna have an impact to the maximum range.
Pros and Cons of High Power VTX
It’s natural for beginners to think “I should use high power VTX because it gives me further range”, but that’s not the whole story.
High power VTX like 600mW is a good choice if you often fly outdoor alone, behind obstacles such as trees. You might get a more reliable signal with better range than using smaller power VTX.
However, there is a diminished returned in range with increased VTX power, some of the energy simply turns into heat and gets wasted. That’s why you often see high power VTX comes with massive heatsink.
High power isn’t always a good thing either when you fly indoor like in a garage. It might have the opposite effect because the strong signal keeps bouncing off the floor, ceiling and walls, which can cause interference. A lower power VTX such as 25mW can typically perform better in these situations.
Furthermore, 600mW are too powerful and might bleed into (interfere) other pilots’ signals making it difficult to fly together. That’s why a lot of races would require pilots to run 25mW VTX.
Pro’s of High power VTX:
- Longer range
- More reliable signals when flying solo
Drawbacks of high power VTX:
- Affects other pilots’ signals
- More heat (how to fix overheat VTX)
- Increase the chance of multi path and interference in indoor flying
So What Power Level should I choose?
It depends on the situation really, so a power-switchable VTX would be preferred.
25mW is great for indoor flying and small races with many pilots; 600mW for long range solo flying; and 200mW would be a good balance between the two.
200mW and 600mW sound like a big difference, but in reality they are not when it comes to range. To get double the range, your VTX power needs to be quadrupled (4x) in theory. So a 600mW doesn’t even give you double the range compared to a 200mW.
It’s not unheard of to achieve 1KM range with 25mW VTX, so 5.8Ghz 200mW VTX should handle 2Km-3Km range easily with correct setup. Especially with mini quads, we don’t tend to fly long range with them. If you really need longer range, the 5.8Ghz spectrum isn’t where you’re going to find it anyway, you should be looking at lower frequency.
There is also restriction on how much power you can use legally on VTX, so please check and follow your local regulations.
Channels are the preset frequencies you can use to broadcast your video back to the video receiver. In 5.8Ghz there are now over 10 bands and 80 channels available (as on Apr 2017). But your video receiver must be compatible with these channels in order to work.
If you only fly alone, then you don’t need many channels as you can only use 1 at a time :) But as soon as you start flying with other people, it becomes important to have more channels available to allow easier frequency management.
How Easy Is It to Change Channel?
You can normally change VTX channels via one or multiple of these ways:
- dip switches (using a needle or small screw driver)
- push button
By far the push buttons are the easiest when you need to change channels in the field. Even if you’re not flying with a club, you may need to change frequencies to find one with the least interference.
On the other hand, the push button channel selection VTX devices seem to have a higher cost, so if you’re going the low-cost disposable route, be prepared to have a dip switch channel selection paper on hand when you need to change frequencies during a race.
One drawback of push button is that when you change channel in the field, you are going through every one of them and you might stumble on the ones someone is flying with, and cause them to crash.
Some VTX’s allow changing channel/settings using an external remote, such ImmersionRC Tramp HV and their wand.
Antenna Connector – SMA or RP-SMA
VTX antenna connectors exist in 2 types: SMA and RP-SMA. Make sure they are compatible with the connectors on your antennas.
If you are not sure which one to choose and you haven’t bought any antennas yet, just go for SMA and stick to it as it’s a more popular choice (no obvious reason).
You can also get SMA to RP-SMA converters if you have incompatible VTX or Antenna. But there is performance loss for every adapter you use.
Connector can be soldered directly on the VTX, either in a straight or 90 degree angle. Or they can be soldered on a “pigtail” that extends from the VTX. Choose whichever you find convenient for your mini quad frame.
Input Voltage and Output Voltage
Some VTX can be powered directly from 6S LiPo (25.2V), while some others only support up to 3S (12.6V) or even lower. It all depends on how you want to power the transmitter and what voltage range you need. We recommended to power your VTX with filtered, regulated 12V to avoid voltage spikes and electrical noise from your power system.
Certain video transmitters are capable of providing 5V output to power other deivces, such as FPV camera, OSD, or even your flight controller. It helps with simpler wiring in some cases, but make sure you don’t draw more current than it’s rated for. Also VTX heats up easily, and drawing more current could make overheating worse.
Some video transmitter might come with built-in microphone that allows audio. Read here about why some pilots prefer audio for FPV. If you’d like to listen to motor sounds during flights, but your FPV camera doesn’t have a mic, then this could be a handy feature.
Support for SmartAudio / Telemetry
This is a relatively new technology which allows you to change VTX channels and settings right from the Taranis TX menu.
It’s now available on all 3 major mini quad FC firmware. However it currently only works on ImmersionRC Tramp HV and TBS Unify Pro VTX.
- KISS – Change VTX settings from Taranis menu
- Raceflight – Change VTX settings from Taranis menu
- Betaflight – Change VTX settings from Taranis menu
Should I worry about NTSC/PAL?
You don’t have to worry about NTSC and PAL for video transmitter. All modern VTX on the market support both automatically.
How to use VTX properly
NEVER POWER VTX WITHOUT AN ANTENNA!
I have to say this loudly in capital letters, because it’s important! If you power up your VTX without an antenna, energy has no where to escape and heat will build up in the transmitter. Eventually it will get so hot and it will burn up! It could take 20 seconds, a minute or 10 mins, god knows, just don’t do it :)
Sometimes it’s easy to forget when you are testing, because VTX and VRX can still work without antennas attached in very short range. That’s because the small SMA connector is acting like an antenna without the presence of a proper antenna.
Any conductive material can be an antenna and emit radio waves.
But it’s not tuned to the correct frequency and heat will still build up in your VTX, and thus the poor range. Same goes to crappy antennas, where you might notice hot VTX and poor range. These work but doesn’t work well.
Prevent ESC voltage spikes
When motors are changing speed, it causes fluctuations in voltage level. With modern ESC these days and powerful “active braking” features, this can cause serious voltage spikes in your power. These voltage spikes might blow your VTX and other FPV components.
Some people try to resolve this by adding large low ESR capacitors to their ESC’s or PDB. Or more effectively against noise in voltage, a LC filter along with a voltage regulator is often used to power VTX and other FPV gear.
VTX antenna and Carbon Fibre frame
Try to avoid letting VTX grounds (antenna ground) making contact with carbon frame. Because if any live wire touched the frame (CF is conductive!), it could potentially fry your VTX. Also it could back feed noise and causes a number of issues with VTX overheating due to resistance.
Protect your VTX
I fly aggressively and crash often, and typically the video transmitter bares the brunt of the crash. The components are exposed to damage and are connected to antennas or coax that get snagged on limbs and ripped off. So a lot of people use an coax extension cable and fix one end on the frame, which removes the stress on the VTX connector when crash.
Check out our latest pick of top 5 VTX for mini quad.
Here is a whole list of VTX that are available for mini quad.
- Created Apr 2016
- Updated Apr 2017 – Added “digital fpv system”, “smart audio and telemetry feature”, “10 bands, 80 channels”,