Maximizing Range and Penetration: Understanding Decibels (dB) and Optimizing FPV Drone Setup

This tutorial explains how to estimate the maximum range and penetration of your FPV drone by using the decibel (dB) values associated with your FPV equipment. Understanding these values is crucial for assessing your FPV drone setup’s capabilities, performance, and limitations.

Some of the links on this page are affiliate links. I receive a commission (at no extra cost to you) if you make a purchase after clicking on one of these affiliate links. This helps support the free content for the community on this website. Please read our Affiliate Link Policy for more information.

A key principle in FPV is that by increasing the output power four times (or by 6dB), you can effectively double the maximum range. But why is this the case? This guide aims to provide a clear explanation of this concept and how to improve your range scientifically .

What is dB?

In FPV, dB, or decibels, can be used to measure signal strength, antenna gain as well as VTX (video transmitter) output power. Decibels operate on a non-linear, logarithmic scale. For instance, increasing dB by 3 doubles the signal strength, but doubling the range requires an increase of 6dB.

So, why use dB? In certain applications, working with dB values is much more straightforward due to the simpler math involved. You only need to add or subtract numbers, without any need for multiplication or division, I will explain in more detail shortly.

dB and Maximum Range

The total dB in an FPV system, known as the link budget, is determined by:

• Antenna gains
• Transmitter power
• Receiver sensitivity

As the FPV signal travels through the air, it becomes attenuated, meaning that the dB of the received signal decreases as you fly further away—similar to how sound becomes quieter at a distance.

By knowing your link budget and accounting for signal loss during travel in the air (also known as free space path loss), you can estimate the range. The maximum range is achieved when the dB reaches 0, so a higher link budget results in a greater range.

Although estimating FPV range using dB is possible, in real-world conditions, the signal can be affected by numerous variables such as background noise, interference, humidity, and more. This makes it nearly impossible to generate an exact figure for how far your signal will travel in feet or meters.

Nevertheless, dB remains a valuable tool to help us understand the potential improvements we can expect when using different components, like increasing the output power of your VTX or utilizing antennas with various gains.

Penetration vs. Range

Penetration refers to the capability of a signal to pass through materials, such as concrete walls. However, range and penetration in radio transmission are fundamentally the same. This revelation often surprises many, but it’s a crucial aspect of understanding how radio signals work. Range is basically signal penetration in open air, in which case, air is the obstacle, unlike the typical obstacle that you might think of, such as walls or trees.

Therefore, the methods we use to improve range, also apply to improving penetration.

Antenna Gain in dB

Antenna gain shown in specs

As you may already be aware, FPV antennas have different antenna gains, measured in dBi (decibel isotropic). This specification is normally available on the product page.

Video Transmitter Power in dB

When using an ImmersionRC PowerMeter, you’ll notice that it displays both mW and dBm readings. VTX (video transmitter) output power is typically expressed in mW (milliwatts). To convert between dBm and mW, you can use these simple equations:

dBm = 10*log10(mW) mW = 10^(dBm/10)

Not a math whiz? No problem! There are numerous online calculators to help you convert between mW and dB. Additionally, we’ve provided a table listing common wattages used in FPV drone VTX’s and their corresponding dBm values:

Remember that increasing by 3dB doubles the signal strength, but a 6dB increase is required to double the range. Thus, upgrading from a 200mW to a 400mW VTX will not double your range but rather increase it by 50%. It’s essential to note that simply increasing output power will eventually result in diminishing range returns. Therefore, when aiming for extended range, increasing output power will only be effective up to a certain point.

Receiver Sensitivity in dB

dB is an incredibly useful way to express minuscule signal strengths. For instance, a receiver may be able to detect a signal as weak as 0.0000000001mW, but that’s quite a mouthful! It’s much easier to express this in dB, i.e., -100dB. And for a signal that is 10 times stronger, 0.000000001mW, that would be -90dB. This makes it much clearer and simpler to understand.

• Positive number dB = higher than 1mW
• Negative number dB = less than 1mW
• 0dB = 1mW

Receiver sensitivity determines the minimum RF power the receiver can detect. The more sensitive it is, the smaller signal it can detect hence the more negative the dB value will be. While it may seem counterintuitive at first, a more negative number indicates a greater range for receiver sensitivity.

Video receiver manufacturers often do not disclose this number, and when they do, its accuracy can be questionable as they tend to be optimistic about their products’ capabilities.

If you can’t find the number anywhere, -85dB is a reasonable conservative estimate for analog video receivers (suggested by this post on FPV lab).

The RX5808 receiver module claims to have a typical sensitivity of -90dB, according to Foxtech. FuriousFPV also stated that the True-D receiver module’s sensitivity is -93dBm +/-5dBm when asked.

If you know the sensitivity of your receiver, please share it in the comments. This information may help someone in the future.

How to Calculate FPV Range with dB?

Simply input the values into this range calculator I made, and it will return the distance in kilometers.

For those interested in the technical details, here they are:

As mentioned earlier, the absolute maximum range can be determined when the signal strength drops to 0. However, when the signal weakens, our video will show static and might become “unflyable.” To ensure a reliable connection, it’s common practice to assume a minimum level of signal strength we should maintain, i.e., the Link Margin. For example, you might want to stay above 10dB or 12dB or even higher to be conservative.

Using the Free Space Path Loss (FSPL) equation (reference) we can rearrange it to:

Distance = 10^((FSPL-LM-32.44)-20*log10(f))/20)

Where

• FSPL (Free Space Path Loss) = TX Antenna Gain + RX Antenna Gain + TX Power – RX Sensitivity
• LM = Link Margin
• f = frequency in MHz

Real-Life Example – The Usefulness of dB!

Let’s use this setup as an example:

• 25mW VTX (14dBm)
• VTX antenna: Lollipop Antenna (2dBi)
• VRX: Typical RX (-90dBm)
• VRX antenna: Lollipop V2 Antenna (2dBi)
• Assuming a link margin of 10dB

Input these values into the range calculator, and it tells us the estimated range is about 0.32 km.

Now, to double the range, we need to add 6dB to our link budget. Here are some options:

• You can either increase VTX output power to 100mW (from 14dBm to 20dBm, 4 times the power)
• Or, use a higher gain antenna on the receiver with a gain of 8dB or more. Only directional antennas offer such high gain. For example, the Menace Pico Patch has a 9.4dBi gain

Implementing one of these changes will theoretically double your range to over 0.64 km. If you implement both approaches, it will quadruple your range to nearly 1.3 km!

You could also use a lower frequency to increase range. For example, with the same variables, switching from 5.8 GHz to 1.3 GHz could increase your range by over 4 times! Check out this beginner’s guide to using 1.3 GHz for FPV.

Keep in mind that these calculations assume perfect flying conditions. In reality, the actual range will likely be shorter due to various factors, which I will explain in the following section.

Other Causes of Signal Loss

Let’s talk in a bit more detail what could be causing signal loss. Real-life range is likely to be less than the estimation due to factors such as:

• Interference and noise in the environment, or from other pilots
• VTX power drops when it overheats
• Antenna orientation (how TX antenna and RX antenna are aligned, check this post for antenna mounting tips)
  • At 45 degree: -3dB
  • At 90 degree: -20dB
  • Two linear antennas pointing at each other = -30dB
• Mismatched Antenna Polarization, learn more about the topics here:
  • Linear and Circular: -3dB
  • RHCP and LHCP: -20dB
• Loss in Coax cable and adapters of SMA, MMCX, UFL (Usually not a lot, e.g. 0.1-0.3dB), see this post for more info on antenna connectors
• Antenna radiation pattern – Omni antennas have weak signal directly above, and directional antennas are far less effective outside of its beam-width. Learn about antenna radiation pattern here.

* Signal loss figures are from this source

Conclusion

While increasing output power can indeed improve your FPV range to some extent, it’s important to follow good practices such as using an appropriate antenna setup. Remember, knowledge is key when it comes to optimizing your FPV range, and with the tips and tricks we’ve discussed here, you’ll be well on your way to achieving your desired performance. Happy flying.

Edit History

• Mar 2019 – article created
• Jan 2020 – revised
• Apr 2023 – revised