From 12c1e689f90c6b6a8e30d2a4669cbb58792b78c5 Mon Sep 17 00:00:00 2001 From: MUSTARDTIGER Date: Mon, 27 Jul 2026 21:46:07 +0200 Subject: [PATCH] wiring-up: explain receiver supply at high telemetry power Closes #493. Nothing on the site connects a receiver reset to its telemetry power setting. Searching the docs for brownout, voltage drop or power draw returns nothing, and the wiring page says only to connect VCC to any 5v pad. Meanwhile the AirPort page tells the user to set receiver telemetry power to maximum, with no mention of the supply. The failure is misleading. The rail dips, the receiver resets, and the link drops and recovers, which looks like an antenna or packet rate problem. The section gives the two signs that separate a supply fault from a link fault: the problem follows the Tlm Power setting rather than distance, and the receiver restarts rather than only dropping packets. The MatchTX note is the part worth having. With MatchTX the receiver follows the transmitter power, and Dynamic Power raises transmitter power as the link degrades, so peak current draw lands exactly when the link is already weak. No current figures or regulator ratings are given. Those vary by receiver and are not derivable from the firmware, so the section stays qualitative rather than inventing numbers. --- docs/quick-start/receivers/wiring-up.md | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/docs/quick-start/receivers/wiring-up.md b/docs/quick-start/receivers/wiring-up.md index 09451baf8..b01f65730 100644 --- a/docs/quick-start/receivers/wiring-up.md +++ b/docs/quick-start/receivers/wiring-up.md @@ -43,6 +43,27 @@ Now that you have some basic info, connect your receiver to any free UART on you ![Receiver-to-FC Wiring](../../assets/images/receiver-wiring-to-FC.png) +### Powering the Receiver + +A receiver draws far more current while it sends telemetry than while it only listens, and the amount rises with the `Tlm Power` setting. A receiver with a power amplifier, set to a high telemetry power, can ask for more current in short bursts than a small flight controller regulator can supply. + +When that happens the supply voltage dips, the receiver resets, and the link drops and recovers. This looks exactly like a radio problem, so it is easy to spend a long time on antennas and packet rates when the cause is the 5v rail. + +Two things point to the supply rather than the link: + +- The problem follows the `Tlm Power` setting instead of the distance. Lower `Tlm Power` and see whether it stops. +- The receiver restarts, rather than only losing packets. A restart shows as the LED returning to its startup or waiting pattern. + +To avoid it: + +- Use a 5v pad that comes from a regulator with enough capacity, not from a rail shared with several other loads. +- Keep the power wires short, and do not use thinner wire than the receiver came with. A long thin wire drops voltage under a current spike. +- If your model needs high telemetry power, consider feeding the receiver from its own regulator rather than the flight controller. +- Raise `Tlm Power` one step at a time and test after each step, instead of setting maximum straight away. + +!!! note "MatchTX" + With `Tlm Power` set to `MatchTX`, the receiver follows the power the transmitter reports. Dynamic Power raises the transmitter power when the link gets worse, so the receiver draws the most current at exactly the moment the link is already struggling. If a marginal supply is going to fail, this is when it fails. + Check for shorts between pads and clean up flux or any soldering residue if you have soldered the receiver yourself. !!! warning "Not so fast!"