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Written by Joshua Bardwell
THE DEAL WITH DRONES
As seen in the June 2020 issue of Model Aviation.

I’M NOT HERE TO TELL YOU whether or not line of sight (LOS) or FPV is the better way to enjoy RC flight. I started out flying LOS as did most people. I enjoyed it, but I felt as though something was missing. The reason I wanted to fly was because I wanted to fly. I didn’t want to watch an airplane up in the sky—I wanted to be up in the sky.

That’s where FPV came in. In an FPV system, a tiny camera and wireless video transmitter are mounted on the aircraft. The pilot wears goggles over his or her eyes, which shows the image from the camera. It feels like riding along inside of a drone!

Until recently, the biggest weakness of FPV systems has been that they use analog technology. In fact, FPV cameras and video transmitters send the same National Television System Committee and Phase Alternating Line video signals that were used by broadcast television. If you have ever watched TV shows from before the mid-2000s, you know why there’s a lot of room for improvement.

Why do we have to fly FPV with a video feed that was invented in the 1950s? Why can’t we have high-definition (HD) video? We finally can. Digital HD FPV systems have arrived.

The two systems that I will focus on are the DJI HD FPV system and the Fat Shark Byte Frost system. In my opinion, these are the only viable systems in production today. The Fat Shark and DJI systems beat their competitors in terms of range, link reliability, size, and weight. Most importantly, they come from reputable companies with a long history in the hobby that have been proven to deliver great build quality, customer support, bug fixes, and feature upgrades.

analog goggles arent dead yet
Analog goggles aren’t dead yet.

The main advantage of a digital HD system is easy to understand: high definition. Think about how bad television from the ’90s looks now that you’re used to HD video. Enough said.

A less obvious advantage of digital systems is the ease of management. Analog transmitters rely entirely on the users to avoid each other’s channels. When someone else powers up on your channel, you lose video and crash. With digital systems, channel selection can be automatic, eliminating this concern.

The DJI system offers a combined control and video link. If you use the DJI controller, you don’t need a separate receiver in the quad because the DJI Air Unit acts as the receiver. It outputs S.Bus to your flight controller, similar to how any other receiver would. This greatly simplifies wiring, especially with newer flight controllers that are designed to be plug-and-play compatible with the Air Unit.

Digital FPV systems also have disadvantages though. They are more expensive than analog ones. The DJI goggles are approximately the same price as the premium analog FPV goggles that are available. The DJI camera and Air Unit are close to three times the price of a typical analog camera and video transmitter. The Fat Shark Byte Frost system is less expensive, but still costs more than analog.

Although the weight of digital systems is low enough to make them viable for general use, they’re still heavier than analog systems, especially the tiny ones that are used on micro quadcopters. The smallest quads that can carry a digital FPV system use approximately 2.5-inch propellers.

blockiness as the image breaks up
The DJI system’s image, shown on the left, has a high resolution with "blockiness" as the image breaks up. The analog system’s image on the right shows lower resolution with static.

If you’re using digital, your friends can’t tune into your video feed with their analog goggles. DJI goggles transmit a two-way datalink, which means you can’t stand near other pilots while you fly or your goggles will cause interference for them. The DJI pilot ends up standing 20 feet away from everybody else, which can feel a little lonely. The Fat Shark Byte Frost is a one-way link and doesn’t have this issue.

One of the biggest challenges of digital FPV systems is reducing the latency of the link. DJI has reduced the best-case latency of its system to approximately 25 to 35 milliseconds, which is not as fast as the fastest analog systems, but it’s similar to typical analog equipment. The problem with the DJI system is that the latency increases unexpectedly as the signal strength goes down. Average pilots don’t seem to notice this, but more experienced pilots—especially racers—seem to be sensitive to even small changes in latency. Fat Shark’s system has consistent latency, more like an analog system.

When an analog signal becomes weak, static appears and the image can flicker or roll. Digital systems don’t do this. The DJI system responds to low signal strength by reducing the effective resolution of the image. Basically, the image gets "blocky."

Fat Shark has a more "analog" style of breakup, where flickers appear across small parts of the image, but other parts of the image still have full resolution. Some people prefer the stability of the digital-style breakup, while others feel analog-style breakup preserves more information that can be used to fly out of a bad situation. This could be seen as either an advantage or a disadvantage, depending on your preference.

Flight controllers typically support the ability to draw an on-screen display (OSD) on top of the video feed—but only if it’s analog. They can’t handle HD signals. Fat Shark and DJI address this by reading data from the flight controller then putting that data into their own OSDs. But they don’t support the full functionality of the flight controller’s OSD.

For example, the digital system might be able to display the battery voltage and capacity but not the GPS coordinates or direction-home arrow. This limitation is particularly painful when troubleshooting a problem with the aircraft because the OSD is designed to give essential diagnostic information in the field. That information simply might not be available to users of digital systems.

The big question that everyone is asking is whether it is finally time to move to digital FPV. For the first time in history, the answer might be yes. We finally have digital FPV systems that are truly worth buying, but they are not for everyone.

Can you afford it? If you’re on a tight budget, digital FPV is not yet for you. Do you want the lowest possible latency? Analog still has the crown there.

Do you race? Race organizers are not yet set up to handle mixed digital and analog systems. Do you mostly fly quads that have smaller than an approximate 2.5-inch or 3-inch propeller diameter? You’re probably better served by a good pair of analog goggles because your quads can’t handle the weight of a digital system. Is your focus on GPS-assisted flight or other situations where OSD information is mandatory? No digital system currently supports full OSD passthrough.

If these questions did not disqualify you, it might be time to switch to digital FPV. Of course, you’ll only know after you try it for yourself—and you should. It’s easy to underestimate the impact of the HD image, but many skeptics find themselves convinced after they see it in person.

a full dji setup including the controller
A full DJI setup, including the controller.

SOURCES:

MultiGP

www.multigp.com

DJI

www.dji.com

Fat Shark

www.fatshark.com


3 comments

AMA did an excellent job having Joshua Bardwell writing articles for us. He is great!!! Thanks for that.

I’ve been flying fatshark for about four yet now with hd3 googles with True 3D receiver they are good but I was sick of all the static and break up I’ve tried everything I cough buy from different antennas to different cameras and even different transmitters I have so much of this junk here I will never use it. Then I bought the DJI system and WOW it’s the most unbelievable system I’ve ever seen. I will never go back to the analog again and I think DJI will try to improve this system and even make it better. And if it wasn’t for Joshua Bardwell making such great Videos half us would be able to make half of our equipment work this guy is absolutely incredible just would just love to be able to talk to him on the phone.

Need a second and third reading.

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