frsky receiver (3)

What is FrSky Receiver PPM Output?

Let us take a look at what PWM & PPM is, along with FrSky Receiver PPM Output in this article. PWM or Pulse Width Modulation has been the de-facto choice for receiver out for decades and for good reason - it was direct, easy and simple to use. But as the need for more channels came necessary, it wasn’t logical to keep adding PWM channels, each taking an extra pin - enter PPM or Pulse Position Modulation which brings in multiple channels into a single pin.

What is an RC signal?

So, how do the servos on your RC plane or the rotors on your drones get the signal to move the rudder or control rod? Obviously from the receivers. So there must be a standard communication “talk” between the receiver and the servos, right? This is called as the RC signal. It is what enables servos or any peripherals such as Flight Controllers to understand what input the receiver is giving them.

What is a PWM signal?

The first generation of receivers used PWM or Pulse Width Modulation signal. So what exactly is a PWM signal?

A Pulse Width Modulation signal is a way of creating analogue signals from a digital source. Analogue signals are sinusoidal in nature while digital is in binary, ie. 0s and 1s. So to generate an analogue signal(continuously changing signal) from a digital source in a PWM signal, we change the frequency and duty cycle of the signal.

The duty cycle is the amount of time that the signal is HIGH (ON) versus the total time it takes to complete the cycle in terms of percentage. Frequency, on the other hand, is how fast one cycle is completed. For example, 100Hz (Hz or Hertz is the unit of frequency) means that the signal completes 100 cycles per second.

By combining duty cycle and frequency rates we can change how long a signal is in the HIGH state and how long the signal is in the LOW state. By varying these two values, you get an analogue signal (not pure analogue though)

So now that we have got that out of the way, let us talk about why PWM was widely used.

As previously mentioned, PWM just consists of two variables that is needed to be changed, which makes PWM signals extremely easy to be created and decoded by simple devices like your servo.

But as time passed by, pilots started to require additional channels for drones and auxiliary devices. Due to the hardware requirement of an additional PWM pin for each channel, it was quite obviously not feasible to have more than 6 to 8ch via separate PWM signal wires. Hence, there was a requirement to condense multiple channels into a single hardware signal wire.

This is where PPM came into play.

What is a PPM Signal & Why use it?

PPM or Pulse Position Modulation is another scheme used to send signals, but this has the added advantage of sending multiple channels/signals via a single PPM signal wire. How? Read on!

In PPM, each channel is lined up back to back on a single signal train (technically this is not how it works, but for simplicity, we will follow this schema). So, channel 1 is followed by channel 2 which is followed by channel 3 and so on. Once the final channel data is also sent (say channel 8), the pulse train goes back to the first channel and gets refreshed with new channel values.

So with this, we have essentially cut all the extra channel wires down to a single wire thus saving space, hardware pins and complexity of wiring.

So what are its downsides?

The issue is that standard servos do not support PPM signals but rather PWM only. This would not be a deal-breaker for the drone fliers out there but for planes and fixed wings, this could be an issue as they might not be using a flight controller which accepts PPM but rather directly connect receiver outputs to servos and ESCs.

Of course, you can get around by using a PPM to PWM converter module which is available quite cheaply.

Where does FrSky stand?

FrSky obviously has a vast number of receivers, each capable of outputting different types of data as PWM, PPM or the newer S.Bus. Few examples of FrSky Receiver PPM outputs are:





Among others.

In this article, we have seen what are radio receiver signals, what is PWM & PPM and the differences between the two and how FrSky Receiver PPM Output can help you save a lot of wires on your build and how clean the build is with PPM over PWM.


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Review: FrSky X8R Pro Receiver

We will look into the FrSky receiver and answer the question as to whether you should get one for your craft or project over any other receiver. We will also look into the feature list, compatibility and other such details of this receiver and compare it with the FrSky X8R Receiver as well from the previous article. 

Hardware & Pin Layout of the X8R Receiver

The FrSky X8R Pro is identical in every way to the X8R receiver, physically.The FrSky X8R Pro is a receiver that is mainly targetted towards planes and larger size quads or crafts where size is not a constraint and where you need pure PWM pins than S.Bus or PPM. The X8R has a plastic cover to protect it from the elements (which you can remove to save space and weight).

The X8R Pro outputs 8 individual PWM channels and also has an S.Bus port if you want to use with modern flight controllers like the PixHawk or micro quad flight controllers. The 8CH PWM is especially useful when you want to control a lot of servos and systems especially on planes and such systems where PWM is mainly used.


There is also a PWM RSSI output pin for getting Raw Signal Strength Indication for your Flight Controllers.

On the backside of the X8R Pro, there is a Smart Port pinout as well! This is great in case you want to connect external FrSky Sensors or provide telemetry data from your Flight Controller to your FrSky transmitter radio. It is weird that they have chosen to place the Smart Port pins at the antenna side of the receiver than on the right side where all the usual pins are situated; this will bring up an untidy wiring setup. 

Speaking of the antennas, the X8R Pro consists of 2 patch antennas(PCB antennas) instead of the normal dipole stranded wires. What does that have to do with the performance you may ask, quite simply, patch antennas provide more range than dipole antennas. In the case of the X8R, FrSky claims an additional 20% more range! So why not put patch antennas on all receivers? The reason is that patch antennas are highly directional with higher gain than traditional dipole antennas. Simply put, they receive signals very well in a particular direction ( parallel to the antenna orientation ) but have low signal strength in other directions.

This can be useful in some cases where the craft is moving parallel to the transmitter but once it changes its heading, it can lose some signal strength. In most cases, this wouldn’t make much of a difference, so you needn’t worry ;)

On the top side of the receiver, you will find the F/S (Bind) button as well as the two RED/GREEN indicator LEDs.

All the above-mentioned points are exactly as described for the FrSky X8R receiver. The only way to distinguish between the FrSky X8R and the FrSky X8R Pro is by checking for the “PRO” logo next to the R-X8R logo on the top of the receiver.


The R-X8R Pro from FrSky is an ACCST supporting receiver. We have already discussed ACCST & ACCESS in other posts, so we are not diving into that in this one.

The PWM as discussed is 8CH output and the S.Bus pinout would be perfect for stabilizers and flight controllers.

What differentiates between the R-X8R Pro and the X8R is that the FrSky X8R Pro version has higher precision and lower latency. Its deviation of PWM is reduced to 0.5us, and the delay of PWM output is 9ms less than that of the X8R in high-speed mode. A feature that deserves mention is the decreased effect of interference caused by the ignition process.

The Smart Port connector on both the X8R Pro also supports FrSky FBVS from with A2 port for simple voltage monitoring as well as other sensors and telemetry systems from FrSky like the TEMS-01 for temperature monitoring of your craft or engine etc. or another example would be the FSH-01 sensor hub, so you can connect multiple sensors to one board which then relays the data to the X8R Pro receivers for telemetry.

This feature is quite useful in helis and places especially the ones with a petrol or nitro engine where you have to monitor temperature and RPM along with other data.

You can use the S.Bus to output all 16CH from the receiver and in case you need to use 16CH PWM channels, you can get an S.Bus to PWM decoder which will translate the S.Bus signals into individual PWM channels for all your servos.

But that isn't all the FrSky X8R Pro receiver can do. It can also work in the D8 Mode to work with transmitter modules such as the DHT, DJT, DFT and DHT-U. In this mode, you have 8 channels and at the same time, you can use the Smart Port.


Dimension: 46.5mm x 27mm x 14.4mm

Weight: 16.8g

Operating Voltage Range: 4V-10.0V

Operating Current: 100mA@5V

Operating Range: >1.5km (Full Range)

RSSI output: analog voltage output (0~3.3V)

Firmware Upgradeable

Servo Frame Rate: 9ms (HS—High-Speed Mode)/18ms (FS—Normal Speed Mode)

All 16 channels require the FrSky Taranis or the XJT module.

For 8 channels in D8 Mode, you can use the FrSky Taranis or XJT, DJT, DFT, DHT and DHT-U modules.


The FrSky X8R Pro receiver is a great receiver for planes, helis and large drones where you need the full-range capabilities of the FrSky system and breaks out 8 channels of PWM and Smart Port connector with low-latency mode as well.

In the question, whether you need to buy this one, from my experience it is a great receiver with full-range capabilities but since the device runs on the ACCST protocol, I would personally resist from purchasing it, especially if you have the latest FrSky radios with ACCESS firmware. But from legacy builds and testing, this is a great receiver without a doubt!

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Essential RC Airplane Telemetry Technology


When trying to perfect their performance, RC hobbyists, pros, and even amateurs will frequently rely on RC Airplane Telemetry devices and systems, since a capable pilot should learn to better use his/her physical abilities and available technology, searching for ways to not only develop their own skills with practice but also to get as many as possible useful information about their vehicle’s behavior while flying.

With that in mind, one telemetry essential yet basic product that is highly recommended is the FrSky Smart Port RPM and Temperature Sensor. Like many other sensors from FrSky, this one also works with the Smart Port interface and, when installed properly in association with an S.Port enabled receiver, it can send the acquired data to its respective transmitter ‘s digital Telemetry Radio System.

Get yours now for just $18.20 at and improve the safety and performance of your flights!

FrSky Smart Port System

So… what is Smart Port? For those of you that don’t have a clue or never even heard about it in the first place: the S.Port (Smart Port) is a signal wire full-duplex digital transmission interface provided by FrSky Electronic Co., Ltd. and it was developed for the 2nd generation of FrSky systems.

Every S.Port enabled device - sound modules, display modules, sensors (such as the one we are talking about here), and any other device that works with a data interface that is in line with FrSky S.Port protocol - can be directly plugged in and arranged however the user desires, making RC components/device setup much easier than conventional multi-wire looms.

To sum it up, the Smart Port system offers this flexible and superior possibility of daisy-chaining several different components with high precision and without the need of a sensor-hub or other dataset. It is smaller, easier, and faster (approximately 6 times more than a conventional “hub system”), perfect for RC Airplane Telemetry.

RPM and Temperature Sensor

The FrSky Smart Port RPM and Temperature Sensor is a two-in-one telemetry device for RC Airplanes that can measure the RPM of brushless motors and also read the temperatures of other components besides the motor itself, such as ESCs and BECs, glow and gas engine cylinder heads, batteries, mufflers, voltage regulators, tailpipes and even ambient air!

Considering how important it is to know your RC airplane’s motor’s RPM and the temperature of critical components (for performance and safety reasons), the functions in the sensor will prove to be very useful. The RPM reading range (for a 2-pole brushless motor) is 1,000-30,000 rpm and the temperature can range from -20°C to 250°C (degrees Celsius) - 4°F - 482°F (degrees Fahrenheit).


One can notice in the image above that the sensor is small and lightweight (only 8g), which is ideal since it is a device that will not necessarily be used in every flight. 

Mounting and Setting up

As expected from a product made by FrSky, its users will find it straightforward and easy to install by following these steps:

Attach one end of the Temperature Sensor (TEMS-01) to your ESC and the other end to one of the two corresponding sets of pins (T1 or T2) that are mounted on the PCB (Printed Circuit Board).

Next, connect the sensor to any couple of wires from the brushless motor using the supplied JST connector.

Finally, connect the RPM sensor to the receiver (and/or other FrSky sensors) via Smart Port, then turn it on by linking your battery to the receiver.

Now to finish setting up:

Check the number of Pole Pairs in your brushless motor.

Enter Pole Pairs setting mode long-pressing the key until the Red LED is on.

Then, push the key repeatedly until you’ve got the correct number (in Binary) set on the little 4-digit display (0 to 3).

Power off the receiver after set.

Thus, as you can see, this entire installation and setup procedure is indeed quite simple and relies only on the push button and LED status indicator. For more detailed instructions and schematics, check the product manual on FrSky’s website.


Operation Specifics

Do bear in mind that this technology was designed to work with FrSky’s Smart Port interface, meaning that it is only compatible with Smart Port enabled receivers, such as the X8R, X6R, and X4R. Also, before using, please consider that although it can work with motor wires’ voltage range of 7.4 - 44.4V, that is, motors that run on 2S to 12S LiPo batteries, this sensor was made to operate at 4 -10V.


This RPM/temperature sensor can also be used simultaneously with other FrSky Smart Port enabled sensors, including the variometer, airspeed, GPS, lipo voltage, and current sensors, since all of those can daisy chain with each other through their Smart Port.

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