FrSky receiver names and what they mean
Let's make things a bit less confusing when it comes to FrSky receivers. Without jumping too deep into techno mumbo jumbo minutia let's clarify the lingo. We'll go by the newest first and work down. We won't dive too far back in ancient FrSky history.
Digital transmission
Everything has a number associated with it.
To fully understand how the transmission of FrSky transmitters and receivers work you have to keep in mind that it's a digital transmission. The thing to keep in mind is that movie film was made up of what are single image fames on a film strip. The movies were 24 frames a second. That was enough to simulate action in reality. Your FrSky transmitter is similar. Many, many times a second it spits out information about the exact location, of each stick, switch, knob and slider, regardless if you're using them or not. Each of these positions is represented in a numerical value. The transmitter sends a digital transmission, zeros and ones to the receiver. The receiver unpacks the information and sends out commands to the servos, lights, or whatever else is hooked up to it.
Here's a panoramic picture of a park. In order to get the entire park in the frame it was made with 3 different images. The three images are stitched together to make one image. In photography we call this a panorama. In RC, sometimes we have to send too much information to fit neatly in the space we have to work with. If they were instructions written down on a sheet of paper, perhaps we need more than one sheet of paper to give all the instructions?
As you may notice there is an option for SBUS 16 and SBUS 24. A frame is usually 8 channels. Often 8 channels isn't enough, so we have standardized on 16 channels. But in some situations, we'll need 24 channels. Default in your radio is SBUS 16 but you can select SBUS 24 and get all 24 channels your transmitter is capable of producing.
We talk about the transmission of data in "packets." A packet could be 8, 16 or 24 channels. You can think of a packet like an envelope. An envelope can hold one, two or three pieces of paper. But the cost of mailing it will be the same. Just for fun, let's say that one envelope can hold 1, 2 or 3 $20 bills. If I owe you money would you really care about how many envelopes it took me to repay you, or would you care about the total money received? This is why we count frames, not packets.
So, now that we understand why we count frames, not packets, your receiver does one thing that's also very important. It keeps track of the amount of frames it receives. When the transmitter is sending packets it also sends along a count of total frames sent from it to the receiver. Sometimes a packet goes missing (called a dropped packet). The receiver provides information about the total amount of frames received. In telemetry this is known as VALID FRAME RATES (VFR). It's a percent of all the packets it has received compared to what the transmitter's count of packets sent. Obviously, the higher the count the better.
The only other thing to keep in mind is that everything is transmitted with zeros and ones in a serial manor. It's one zero or one at a time going from the transmitter to the receiver. The more frames in a packet, the longer it takes to get all the information from the transmitter to the receiver. This slows down the transmission rate. The transmitter is literally waiting for the receiver to be ready for the next packet. The amount of time that it takes a packet to fully go from the transmitter to the receiver is known as "latency." It's a measurement of lag time.
Protocols
Protocols are a means of communication. By now you've probably figured out that all the different radio transmitter manufactures use different protocol. Even within the same manufacture there are different protocols. For example FrSky has ACCESS and ACCST on 2.4ghz FSK. Protocols are the special sauce that keeps FrSky transmitters and receivers so beloved.
TD Pro- The Tandem X20 Pro uses three protocols on two different frequencies. 2.4ghz FSK and 900mhz. and 2.4ghz LoRa. Let's break this all down a bit further.
900mhz is the easiest to figure out. It's a long-range protocol that offers excellent penetration. Even though you may not fly further than you can see, you'll appreciate the penetration of 900mhz. It's a very, very reliable link.
2.4ghz- There are two different types of protocols on the 2.4ghz band. These protocols are very different from each other.
2.4ghz FSK- It's time to get a bit nerdy. FSK stands for Frequency-Shift Keying- There are a lot of channels available on 2.4ghz FSK and the transmitter and receiver are occasionally changing their transmission frequencies. The things to keep in mind is that this is a means of moving a digital binary signal from the transmitter to the receiver.
FSK digital signals were once state of the art, but are now used by other radio brands. They are very common these days. There are pluses and minuses to this technology. On the positive side, there are many channels to use and this technique means that many people using these frequencies can fly at the same time. Thus, this is great for large flying events where many people all want to fly at the same time. The downside to this the range if a bit more limited and the possibility of triggering a failsafe, even within visual sight is possible. Still, with all this being said, I still fly many planes with FrSky 2.4ghz FSK (both ACCST and ACCESS) and never have a problem.
2.4ghz LoRa- LoRA stands for LOng RAnge. This uses similar technology to 900mhz receivers, and the signal range is fairly similar. to 900mhz. Like 900mhz the number of free channels to use is fairly limited. isn't as broad as 2.4ghZ FSK. One other side benefit is the antennas for this technology are smaller than the 900mhz T-antenna. Thus they fit better in DLG gliders and small drones.
FrSky is the only supplier of 2.4ghz LoRa that works on 24 full range channels. This technology is truly state of the art.
The Tandem X20 Pro is the first transmitter to work with the new TD Pro protocol. Starting in 2024 there will be a receiver that can receive 2.4ghz FSK, LoRA and 900mhz at the same time!
Twin (TW)
The newest line of dual band transmitters and receivers Twin is both 2.4ghz FSK and 2.4ghz LoRa. The FSK offers a wide array of usable channels and the LoRa offers penetration similar to 900mhz. Due to it's smaller antennas than 900 mhz T-Antennas the Twin receivers are beloved by people who fly small discuss launch gliders (DLG).
The 2.4ghz FSK signal tends to be the most open band with the most amount of channels. The receiver prefers this as the primary means of communications.
Tandem TD This is the protocol found in the Tandem XE, X18 & X20 line of transmitters. It works on 2.4ghz FSK and 900mhz. The 2.4ghz FSK allows the transmitter to work on a broader range of channels. When the signal degrades, and the 2.4ghz packets that are successfully receives below a certain threshold, the Tandem fills in with the 900mhz packets. The Tandem transmitter broadcasts on both bands simultaneously. FrSky is the only manufacture to offer both 2.4ghz and 900mhz receivers built into the same receiver unit. FrSky offers multiband diversity built into the same receiver. Other brands make you purchase two receivers to do the same thing.
ACCESS
ACCESS is the newest of the 2.4ghz FSK receiver protocols. It stands for
ACCESS (Advanced Communication Control Elevated Spread Spectrum). This was a feature rich upgrade from ACCST. It included
over the air firmware updates - this is definitely my most favorite feature. You can finally update your receivers without having to physically connect them to your transmitter.
up to 24 channels, that is eight more than D16 had
Lower latency: Depending on the amount of channels:
8 channels: 11ms
16 channels: 14-23ms
24 channels: 14-23ms
Automatic binding: also called Smart Match. Binding is now a two step process. You first register your receiver to your transmitter, once this is done you can easily bind to it without pressing a button. This makes things easier when you want to use a receiver once again with a new model on your transmitter.
Bind multiple receivers with one model - this is useful if you want receiver redundancy, in case one receiver flakes out on you, you simply switch to another one. This is especially interesting for big, really expensive models where you want redundancy . The great thing about this is, that all 3 receivers are capable of transmitting telemetry back to the transmitter FrSky calls this Trio Control.
ACCST
A lot of the older receivers have D, V or X in their name. There was an LR12 receiver that was the forerunner to the 2.4ghz LoRA receivers we're using today.
Codes
S-Stablization- The SR12 and S8R are stabilized receivers. This is a much longer topic, but the stabilized receivers are a bit of work to setup the first time, but so worth it. Once you have one you'll have more.
R-Redundency- This means that the receiver has SBUS in which allows a second receiver to be added to the receiver for increased security.
G- Glder- The glider has a built in variometer which allows for vertical airspeed and altitude telemetry.
TD R10- One of our best selling receivers, it's part of the Tandem (TD) line which makes it dual band 2.4ghz and 900mhz. R for redundency, 10 for 10 channels.
TW SR12- Twin protocol, stabilized, redundency, 12 channels.
GR8- Glider receiver, with built in variometer, redundency, and 8 channnels.
Archer M+- Trick question. The name Archer means its a 2.4ghz receiver. It's a receiver that was formally known in the ACCST days as XM+. This was a drone receiver. The M may have stood for miniature.
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