Diversity receiver technology is a significant part in FPV and RC models. To get the best signal both of the antennas must be lined up parallel. That's great in theory but in the real world when you're flying along, sometimes the antennas don't line up easily. This will indeed cut off the signal.
Almost every smartphone or even the good old keyboard phones are manufactured with dual sim card capabilities, where each sim slot works independently of each other. When moving around, based on the signal strength to the nearest tower, sim card signal strength varies.
In the same context, Diversity receivers make use of two or more receiving modules, up to 6 receiving modules; in the case of Quanum Overlord Diversity receiver, to increase the amount of signals received.
Nowadays, radio receivers are also being introduced with diversity receivers, to increase the range of the quad while also maintaining a good signal strength flying close range.
What is Diversity in FPV?
Receiver diversity is one of the common types of the technology used. They generally have four working parts:
- Two receivers.
- An antenna on each Receiver
- RSSI (Received Signal Strength Indicator)
- A switch between the receivers and the screen.
Diversity in the literal sense means a variety, or in Quad terms more than one. Traditionally receivers, both Radio and FPV Video receivers, made use of a single receiving module. Radio and Video receivers process the input based on the amount of RSSI received by them, also known as Received signal strength indication.
(RSSI) is calculated in terms of percentages. As the Quad moves farther away from the pilot, the amount of Radio and Video signals received diminish due to various factors such as the distance between the quad and pilot, Radio Transmitter losses, external noise to name a few.
But with increasing competition amongst the manufacturers and FPV pilots pushing the limits of technology, manufacturers came up with the idea of Diversity receivers. A Diversity receiver makes use of 2 or more independent receiving modules, which in theory should double the amount of signals received, but the real-world gains are much lower.
Diversity receivers work based on the principle that whichever receiving module inside the receiver has a higher RSSI value, that receiving module gets the preference. This switching between the receiving modules is an automatic process that the receiver takes care of internally and happens almost instantaneously, we humans can barely notice.
Well the basic idea is to have one receiver with two antennas and the concept being that whichever antenna gets the strongest signal will be switched into the receiver. But how would you know?
The RSSI comes out of the receiver, so how are you going to know which receiver is stronger?
Some might think it should work without a difference. But there is a significant difference and that's one being Analog and the other Digital.
Digital DIVERSITY System
Let's assume we have a digital system. We can do antenna diversity with digital really easily and that's why most of our modern 2.4 gig receivers uses this.
The signal comes from the antenna as a packet of bits. There is a type of data that precedes this and is called preamble.
The chipset used has enough time to look at the preamble by switching back and forwards to determine which antenna is going to be best to receive the packet.
Once it finds which antenna gives the best signal, it'll stay switched onto that antenna until it's received the whole packet. So it has enough time in advance to take a quick check which antenna is working the best.
When the packet has been received, it will start doing that check again. So for every packet of data it checks the preamble to see what antenna is getting the strongest signal.
Analog DIVERSITY System
Here the signal we get from the transmitter is not a packet of data. it's a whole lot of varying signals and it is broken up into what we call frames.
But there's no signal to look at and make sure we got the right receiver antenna. So if we start working on one antenna and we then we will switch to the other one. But then if the other antenna that we switch to is not getting a strong signal we had a dropout in a video.
This forbids us from arbitrarily switching antennas. We would be getting a glitch when we switch from strong antenna to the weak antenna as the system doesn't do a pre-check. So it's really not as practical as the digital system.
One of the problems with the analog signals is when you've got a lot of strong signals on adjacent channels. This can really screw up the antenna diversity.
So it needs to be tested in the field with four or five people flying at once and just see what happens with it's antenna diversity.
Types of Diversity Receivers
There are 2 main types: Video Diversity Receivers and Radio Diversity Receivers.
When the RSSI or the quality of the received radio signals by the receiver is too low for the receiver to process, the quad automatically falls into Failsafe where total control of the quad is lost.
When the quality of the received signals of the Video receiver is too low, the snowflake screen is introduced by the receiver to make up for the loss of signals, and when the quality is too low, total loss video occurs.
Radio Diversity Receiver
One of the main reasons for Radio receivers going into Failsafe is improper placement of receiver antennas. The FPV frames are made of a material called Carbon fiber. This carbon fiber is notorious for blocking RF signals. As the quad is flying through the air doing aerobatics, the antennas might get behind the carbon fiber body and might lose the signals.
Diversity receivers tackle this problem by placing 2 receiving modules. The general understanding is that no matter what the orientation of the quad is, at least one module receives the signal and is always in contact with the Radio transmitter.
The receiving antenna’s center core is what receives the radio signals from the transmitter. It is advisable to place these receiving tips at 90° to each other for the optimum working of the antennas. You must also check the antennas for any damage after a crash if damaged must be replaced without hesitation.
Video Diversity receiver
Another type of diversity receivers used is the FPV Video receivers. Notice the 2 different types of FPV Antennas? Diversity in Video receivers works a little differently. An omnidirectional antenna works well when the quad is flying closer to the pilot and the patch antenna works great when the quad is farther away from the pilot, with the relative movement of the quad very minimal at long distances.
Video receivers also switch automatically between receiving modules and the module with the highest signal gets used by the receiver. Some of the expensive Video receivers have also been introducing a nifty feature called Video Stitching. Receivers compare the video received by both the receivers and essentially take the best features from both the modules to combine into one crisp image.
With FPV venturing into the world of Digital FPV systems, HD video systems, quite notably from DJI, Video transmitters are also diversity in nature for efficient transmission and receiving of Video. DJI HD goggles also make use of 4 receivers rather than 2 receivers.
Bottom line is Diversity receivers are great for either Radio and Video receivers. That said, radio receivers only prove their worth only when the distance between you and the quad is significant. Close proximity flying doesn’t really require diversity and the money saved from a normal receiver can be put to good use, we know how expensive this hobby can get!!! Are diversity Video receivers worth it? Definitely a yes!!!