General ~ FAQ

• What is the minimum hardware I need to try this? Two Raspberry Pi, two WiFi dongles, one Pi cam, and 2 micro sd cards. Please read the rest of the wiki and do your homework when you make your purchases! Some Pi aren’t compatible, most WiFi dongles won’t work, and you need big enough micro sd cards.

• What is the lowest latency I can achieve? 110ms “glass to glass”. Although most setups are in the 125ms range.

• What kind of range can I expect? Depends. Common setups easily achieve 1-3 km. Long range builds have achieved 30 km and more!

• How long does WBC take to regain a lost “connection”? Instantaneous. WBC behaves similarly to analog radio. If the signal is disrupted it will come back almost instantly once the interference is eliminated.

• When I lose connection will I see a “blue screen”? WBC does not generate a solid blue screen when interference is encountered. If experiencing a loss of signal you will see progressive artifacts and pixilation, finally the image typically freezes. The telemetry and/or rc link is more robust and will often continue to operate well beyond the loss of the video stream.

• What are my WBC frequency options so I don’t conflict with my rc transmitter? Best solution is use WBC for RC-control as well (All-In-One System, AIO). Besides ease of use it will give you maximum range due to lowest possible HF-interference (even if you consider using other frequencies like e.g. UHF). Otherwise WBC can run on 2.4ghz(most common) or 5.8ghz depending on your WiFi dongles. Some dongles are capable of 2.3ghz, however interference has been reported with 2.4ghz transmitters. You also need to adhere to your local regulations and laws. 2.3ghz is prohibited in most countries.

• What is a Raspberry Pi? A computer on a single circuit board. In this case running a derivative of Linux. Don't worry you do not need to know anything about the software side, we have that covered!

• Do I need a WiFi dongle for video, another for telemetry, and another for rc control? No. At a minimum one WiFi dongle per pi is all that is needed. You can use more than one transmitter dongle however to achieve what is referred to as diversity.

• Can I run WBC on this other board (Orange Pi, Banana Pi, BeagleBoard)? Short answer, No. Several limitations apply: WBC OS is raspian, the AirPi requires a raspivid compatible camera, the AirPi makes use of Broadcom gpu natively outputting h.264, code is optimized for the Pi. NOTE:There is some flexibility on the Ground side.

• Can I use this other WiFi dongle that’s not on the list? Perhaps but most likely not. We welcome testing but WBC relies on WiFi capable of monitor mode and packet injection. Only some chips are capable of this and then must have compatible drivers.

• Why can’t I just use the pi onboard WiFi for WBC? Currently the built-in WiFi does not have the driver support in order to achieve monitor mode and packet injection. The Nexmon project has had limited success but testing has revealed low data injection rates with the Pi.

• Why am I getting artifacts in my video? There are many possibilities. You might be experiencing interference from other WiFi users- find a better frequency or “quieter” location, AirPi and GroundPi are too close together, RC transmitter interference, poor wiring, low amp/voltage power, bought a fake/wrong/faulty WiFi dongle, incorrectly changed a setting, overheating issues, signal blocked by obstacles. For the best experience use more than one WiFi dongle on GroundPi.

• Why do I get a low power warning? Most likely your are using a unsuitable Power Supply that lacks either voltage or amperage or you have deficiencies in your wiring (too thin wire gauge). Please refer to the Proper Wiring and Power Supply (BECs) sections.

• How many WiFi dongles can I use? Maximum of 2 WiFi dongles for the AirPi. For the GroundPi a maximum of 3 Atheros WiFi dongles or 5 Ralink (or combination of 2 Atheros and 2 Ralink)

• Where are you buying this hardware? All hardware used in this project is readily available standard equipment. It can be found at the common suspects: ebay, Amazon, banggood.com, AliExpress, ... - you name it! The only challenge is to chose components which are compatible with the project so checkout out the Supported Pi models and Supported WiFi Adapters section first.

• Is this legal? Probably. WifiBroadcast uses standard Wifi hardware. However, it's using monitor mode and packet injection, which is not an official or standard way of operating that hardware. Some frequencies such as 2.3GHz and high power settings might not be legal in your geographic area. Do your own research before you power on and make sure you don't interfere with other users of the spectrum. We are not responsible for misuse!

• Can someone else watch my video stream? Yes! This is due to the Broadcast nature (hence the name: WiFi-Broadcast) of the system. You can receive the stream with any GroundPi that is configured to the same frequency as your AirPi. This way you can basically broadcast your signal to an infinite number of viewing devices.

• Where did my recorded video go? See Ground Recording section.

• Why is the OSD not on the video recording? EZ-Wifibroadcast uses multiple/separate screen layers to render video and OSD. This is a necessity to keep latency low. The Raspberry camera directly delivers its output to the hardware H.264 encoder where it is compressed in real time and transmitted to the GroundPi. In parallel telemetry data is send alongside this video information. The GroundPi then decodes the video and renders the OSD on top of the video. Embedding the OSD information would requite additonal frame-buffers and re-encoding the enriched video, hence inducing additional lag and latency.

• What is diversity? A technique to improve the reliability and quality of our WiFi transmission. Multiple antenna and WiFi dongles are used to send and receive signals of slightly different quality which are then combined to get the best result. WBC supports both transmit and receive diversity however in practice most users only add multiple WiFi dongles to the GroundPi. This is perhaps the single biggest improvement you can make for a better experience. Be aware that diversity on digital systems works far more efficiently because digital packet data can be combined whereas analogue diversity just chooses the overall better signal.

• What is FEC? Forward error correction. In addition to diversity, FEC improves the reliability of the data received by encoding the video frames using an error correcting method. It works at the expense of bandwidth. More FEC can also influence how quickly a corrupt image can recover, more FEC can increase latency, and decrease quality. FEC is part of a balance between number of data blocks and length.

• Is latency going to improve in future updates? Hopefully. There are still some things to be optimized, if you are a developer and interested in lowering latency, please have a look here: https://github.com/rodizio1/EZ-WifiBroadcast/wiki/Development-~-Room-for-Improvement

• How much transmission power is being output? This depends heavily from the Wifi adapters used (see supported WiFi adapters) and Transmit power settings configured in software. Generally speaking this can range from 10mW to several Watt. Most cards are set to maximum power by default.

• What do these numbers mean on the OSD display? See the "OSD RSSI and packet display" section in Telemetry and OSD chapter.

• Which rc protocols are supported? The AirPi can output MSP (Multiwii), SUMD (Graupner), IBUS (FlySky), or SRXL (Multiplex), and Mavlink. Note that Mavlink is sending RC control override messages directly to the flight controller. Currently this is the most elegant way to have RC control and bi-directional telemetry combined using a single serial port. NOTE: We are referencing the protocol your flight controller understands, your transmitter or joystick will plug into the GroundPi with a usb connection.

• Which telemetry protocols are supported? Mavlink V1, FRSKY, and LTM will work with the OSD. Mavlink may have additional support for rc control and full bidirectional telemetry depending on your flight controller.

• What is an AirPi / GroundPi? Since EZ-Wifibroadcast is a bi-directional link both Raspberries (on the aircraft and at the ground) transmit and receive. Therefore at times it can be confusing and misleading to talk about TX (Transmitter) and RX (Receiver). Hence new terms were formed "AirPi" = Raspberry on the aircraft; "GroundPi" = "Raspberry on the Ground.

• How about Circular vs. Linear polarized antennas? Circular antennas are known to be very effective in suppressing signal reflections (multipathing) which degrade quality of analogue transmissions a lot. Digital systems are not affected by multipathing though (and often can even make use of it), so circular antennas are not as important like it is the case with analog video systems. However, circular antennas still have some advantages compared to linear antennas:

  • Work independent of angle to each other, almost no polarization losses
  • Typical transmitter antennas have a lower gain and thus higher opening angle than linear antennas
  • Less susceptible to signal blocking from nearby solid objects

• How can I support this project? Spread the word! WBC is relatively young and unknown, the more users we can attract, the more contributors can potentially work to improve WBC. You can also contribute by suggesting bug fixes, enhancements, perform testing, and get involved right here on Github.