How Antenna Gain affects Range in FPV

by Oscar

Antenna gain determines your maximum range, however antennas don’t simply amplify radio signals without costs, it just changes the radiation pattern which is a trade-off between coverage and range.

Antenna Gain In A Nutshell

An ideal isotropic antenna with 0dB gain, radiates signal equally in all directions with zero losses (think of a sphere). But it doesn’t exist, there are directions in which a real antenna will radiate the strongest, and others in which it doesn’t radiate at all.

This is why a typical omni-directional antenna would have a low gain between 0dB to 3dB, and it can radiate signal fairly evenly in almost all directions, more like a doughnut shape but not a perfect sphere.

Directional antennas have much higher gain, and they focus the signal into one direction in order to achieve more range.

Every antenna receives the same way as it transmits, so an antenna’s reception gain is always the same as its transmission gain.

For a basic overview of FPV antennas, make sure to check out these guides:

Antenna Gain and Directionality

Antenna gain is the measure of antenna power in decibel (dB), which is equal to 10*log(Pout/Pin).

Don’t worry about it, just remember that the higher the gain, the more directional an antenna is – more range, narrower beam width.

A 3dB increase in gain doubles the signal power, and a 6dB increase doubles the range. However, as mentioned, directional antennas are not amplifiers. It’s only focusing all the energy into a narrower beam.

A water balloon is a good example.

The volume is the total power of your VTX (or think of it as the signal coverage), and it doesn’t change no matter how you squeeze it or pull it, it’s still the same amount of water in there.

By using an antenna of different gain and radiation pattern, merely changes the shape of the balloon. The balloon might become longer, but the width becomes narrower, and so the total volume is still the same.

A different analogy would be a light bulb vs. a torch, which represent an omni-directional antenna and a directional antenna.

Although signal reception becomes narrower with increased antenna gain, a common technique is to use a diversity receiver. It allows multiple antennas working together, constantly checking signal strength of each antenna and pick the one with the strongest signal. This way we have longer range and wider coverage.

Once you understand the basic concept, you can check out how to use antenna gain (in dB) to estimate range.

Radiation Pattern

Every antenna has a different radiation pattern.

A radiation pattern of the hypothetical isotropic antenna at 0db gain. It’s a nearly perfect sphere in both vertical and horizontal axis.

antenna-gain-0db

This is a standard omni-directional 3dB rubber duck antenna. Notice it has significant signal loss on the top and bottom (90/270 degree). Similar radiation pattern applies to most omni-directional FPV antennas out there.

As you can see the gain actually changes depends on the direction you look at it. So when we speak of an antenna’s gain, we really mean its maximum gain in a certain direction.

antenna-gain-3db

In 3D this radiation pattern looks like a doughnut :)

And here we have a directional antenna of 8dB (a patch antenna). As you can see, majority of the signal focuses on one direction, and not much range at the other end.

antenna-gain-8db

How to Increase Range?

There are normally 2 ways to increase range of your FPV system: to increase the power of the video transmitter, or use higher gain antenna on the receiver end.

Increasing VTX power would be the last thing I would suggest, simply because it might not be legal, and it will consume more power and generate more heat. Try upgrading your antennas first and find the best combination for your specific application and flying style.

It’s a common practice to use an omni-directional antenna (low gain) and a directional antenna (high gain) together on a diversity receiver. This brings the best of both worlds, great coverage and long range.

Edit History

  • Oct 2013 – article created
  • May 2017 – article revised
  • Feb 2019 – article updated
  • May 2021 – revised

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5 comments

Bill 28th May 2021 - 9:53 pm

@the person asking for a directional omni- look into the mx-air.

Oscar Liang is right that there’s technically no such thing, but officially the mx-air is such a compromise.

Truerc is making antenna with all sorts of patterns, but they all obey the laws of physics as described in this post.

Reply
Jack 26th May 2021 - 10:26 am

Hi Oscar,

My goggles is Fatshark recon v3 and has no diversity.

Are there any sort of 2-in1 attenna with both path and omni together?

Or are there any good omni that can do good range.. I am just looking for 1-2km thats all. I have Flywoo Explorer lr 600mw vtx.

Thanks,

Reply
Oscar 26th May 2021 - 12:22 pm

No, you just have to use an omni-directional antenna on it to be safe.
You can estimate range using this calculator: https://oscarliang.com/js/fpvrange.html
Using Omni antennas (e.g. 2dB) on both ends on 600mW you can get 1.5km range at best.
Check this post for antenna recommendations: https://oscarliang.com/best-fpv-antenna/#the-best-fpv-antennas-for-mini-quad

Reply
RCSchim 12th January 2016 - 3:39 pm

Hi Oscar, great blog and I read lots of your articles already (especially when learning about Naze32, Cleanflight and PID tuning).

Have you seen this thing here:
celestialreach.com/Products/ClearBoost-Enhanced-FPV-Drone-Video-Reception

Would be interesting to see what someone with your knowledge think of it. I’m a bit sceptical that we get a lot of gain on the receiver side – but it would be way more elegant than using 10watts in the air ;-)
greetings, RCSchim

Reply
Jamal 20th December 2015 - 9:42 am

I want to ask what is affected by the transmitter signal in 5.8ghz ?

Reply