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Pick your radio control system

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When you start FPV, you probably already have, or had a plane with a radio control system. This aim of this page, is to help you check if your radio is going to be trouble free during your FPV experience, and to explore reliable alternatives or new radio control systems if you have currently none.

The radio control is the link to your RC aircraft, vehicle and is therefore very important. Should it fail you, recovering your model can be very difficult and not always successful.

While we are going to go into some more details, the recommended beginner radio is a FM radio, later extended by a UHF radio system.

Generalities about radios

There are many kinds of radios, however, in most cases you will want to privilege the programmable ones with 8 or 9 channels PPM, and supporting extension modules.

While none of the arguments in this list are requirements for FPV, they are recommended for the following reasons:

  • 8 or 9 channels (or more): FPV often use extra channels for switching displays, cameras, moving the camera around, etc.
  • Programmable: Nearly all of the radios with 8 channels or more are programmable. This let you assign switches to the proper functions and more.
  • Extension modules: you will be able to upgrade to a better radio link in the future, longer range, better reliability, etc.
  • PPM signal: this is the most common signal, shared among radios. This ensure your equipment will be compatible. Nearly all FPV specific equipment only supports PPM out of the box.

Signal type

A short introduction on the most common signal types:

Analog / PPM (FM)

Older radios, no interference resistance. However, you will see the signal usually degrade nicely when you are reaching the maximum range (glitches).

PPM 8 channel signal has historically become a standard, and newer digital systems generally have an extra PPM input/output, or use the PPM modulation on top of their digital signal.

By design, PPM has a frame time of 22.5ms, which means the minimum control latency (delay between you push the sticks and the model moves) is around 22-25 ms.

PCM (FM) PCM is a digital coded signal that is often used on older radios. Often, both PCM and analog PPM signal are provided. This signal is stronger against glitches, but does not resist interferences particularly well compared to more recent digital systems.

DSSS

Uses a wider part of the band than necessary to transmit the signal. If part of the band is interfered, the copies of the signal are still going through. However, if the whole DSSS band used is interfered, you're out of luck. Some radios, like the Spektrum/JR DSM2 use 2 DSSS channels. These channels are sometimes selected next to one another and might be interfered with by wifi traffic and cameras relatively easily.

FHSS

Jump through the band in a random but predictable order (hopping). The complete band has to be interfered to cut the RC link from these systems. Therefore, they're very good at resisting interferences.

Futaba FAAST and all UHF systems are using FHSS. Some other radios also use FHSS or variants, like AFHSS which also ensure it won't use already in use channels for hopping.

Radio type

Regular FM radios

FPV abilities: Good

Signal: Analog

These radios are the “good old” 72 mhz, 35 mhz, 40-41 mhz and 27 mhz radios. It emit on a fixed frequency and is not convenient when many RC users use this type of radio at the same location. Each RC user has to use a unique frequency which is selected prior usage, and there's a table of frequencies assigned in your location, club, or area, and interferences. This lead to frequent human errors and interferences which break your RC link completely.

However:

  • This kind of radios have been phased out in most places and replaced by newer “2.4 ghz” radios which are able to auto-select frequencies, or share the radio bands without breaking the RC link completely.
  • In most places where people practice FPV there is no other RC user.

In these conditions, the regular FM radios are a good choice. They provide medium range (2 to 4km, or more) and can be found for cheap on eBay and other such websites.

The Futaba 9CAP is an example of very popular radio among FPV users.

2.4 ghz radios

FPV abilities: Mixed bag

Signal: DSSS/FHSS

These radios have generally replaced the FM radios in clubs and are the most popular radios. They usually are able to pick clear frequencies and resist interferences well, even if someone else start his transmitter on the same frequency.

While this sound good, there are quite a few drawbacks on these radios:

  • 2.4 ghz is a high frequency, and works only in “Line of Sight” (LOS), that is, it won't go through trees and other objects very well, compared to lower frequencies radios. This frequency also propagate less efficiently and decrease the range.
  • As previously stated, range is lower (usually around 2km maximum on stock radios)
  • The 2.4 ghz frequency is used by many: Wifi, cameras, etc. Most wireless equipment share the 2.4 ghz band. Flying near a city might cut your signal even with the various interference resistance advantage of these radios.
  • While some radios pick a clear frequency for transmitting, it doesn't know if the frequency is still clear when you will be more than 1 km away
  • A lot of the camera equipment, including the one used for FPV transmit over the 2.4 ghz frequency and are therefore incompatible

While it may work at short distance, a 2.4 ghz radio should not be used together with a 2.4 ghz video transmitter

While there are many other brands, Futaba FAAST radios are recommended over Spektrum radios for reasons seen in the above “Signal type” section.

UHF radios

FPV abilities: Excellent

Signal: FHSS

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The Dragon Link

UHF radios are usually emitting on the 433-435 mhz band. The UHF radios are the best of both worlds: lower frequency, relatively unpopulated and enough bandwidth to provide good interference resistance.

They also usually emit at higher power (500 mW average) than the other radios (80 to 200 mW average).

These radios are found in the form of extension modules, which can be plugged on your radio. Again, the Futaba 9CAP is very popular, as well the the cheap imax/turnigy 9x radios.

However, these radios usually require an Amateur_radio_license to use legally due to the frequency and power used.

An example of UHF radio is our Dragon Link, which has been tested over 25 km.


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