Pushing the limits

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Intro

Practices to maximize FPV range. This does not only refer to video, but also control range and other elemntes of FPV flight.


Aircraft building checklists

This section will provide checklists that should be followed when a new aircraft is built/configured/tested. These may include mechanical tests (test servo linkages for sloppiness) to electronic measurements and failsafe testing.


RFI/EMI checks

Steps

The following steps should be followed to ensure that interference between components of the user is minimized:

  1. List all the transmitters you have on board or not, including noisy devices. E.g. vTX, rcTX, Mobius/GoPro, MinimOSD, UBECs, ESCs.
  2. List all the receivers. E.g.: GPS, rcRX.
  3. If something both receives and transmits (telemetry radio, or rc RX with telemetry) include it in both lists.
  4. For each item in the receiver list, find a spectrum analyzer (SA) that covers the frequency used. If an RF Explorer is available it can be used to check everything. UHF receivers can be used in spectrum analyzer mode to check their own frequencies. Cheap TV cards can be used as SAs for frequencies up to ~1.7Ghz.
  5. For each item in the receiver list, plug its antenna to the respective SA and place it in the position that the receiver's antenna normally is. Tune the SA to look at the area of frequencies that is used by the receiver. Then run the following tests and take measurements:
    1. Everything OFF, apart from the SA.
    2. Everything ON, including the SA. Now, if the resulting graph looks similar to the previous one, stop and go to next receiver. Otherwise continue.
    3. Turn each of the items in the transmitter list ON or OFF and record the graphs.
    4. Repeat step 3 for all transmitters. Ideally each transmitter should be tested by itself (while all others are OFF).

In the end you should have a clear image of which transmitter interferes with which receiver. Then one can try solutions to mitigate the problem. E.g. for vTXes, one can change channel (makes a huge difference). Noisy cameras can be shielded by aluminum/copper tape.

Interesting Examples

A 1.3Ghz vtx interferes with a 433Mhz rcRx. Yes, in theory it shouldn't, since 1300>433, but it does. Choosing between two different channels of the vtx makes a big difference:

OpenLRS vtx chan9.pngOpenLRS vtx chan4.png

The first channel (9) is much less noisy than the second (4). In fact, comparing channel 9 to a graph while the vtx was off yields almost the same results, so channel 9 is a good option