RFD900+ powered directly from Pixhawk2?

http://ardupilot.org/copter/docs/common-rfd900.html has a warning that says

These modems are high-power RF devices. It is suggested to provide separate +5 voltage to the modems. It is NOT suggested to power these modems directly from Autopilots telemetry port

Does this also apply to the Pixhawk2 from @proficnc? Isn’t the telem1 port properly powered for this modem?


This radio needs it’s own power supply. Please follow the wiki on this.

Bask and others make great breakout boards that can help with this.

http://www.hex.aero/wp-content/uploads/2016/07/DRS_Pixhawk-2-17th-march-2016.pdf says

Serial 1 has a private 1.5A current limit, intended for powering a telemetry radio

The spec of this radio says http://store.rfdesign.com.au/rfd-900p-modem/

~800mA max peak (at maximum transmit power)

@proficnc Could you please elaborate why it needs its own power supply?

Is there a standard way that these are being powered separately? The jdrones RFD 900+ come with a 6 pin JST-GH connector. How would I power this separately with this interface?

You take the jumper off the other set of pins and supply a dedicated 5V supply. If you need a picture a can take one of my antenna tracker. Its fairly straight forward.

This is a great question and I also referenced hex documentation when I decided to power my RFD 900+ from my pixhawk 2.1. I haven’t had a problem with yet, but obviously I want to do what is suggested.


Basically there have been reported brownouts on startup, perhaps not directly due to the rfd900 but in the absence of a more attributable cause, and in the interests of safety, we now recommend independent powering of the rfd900. Chances are you’ll be fine off the flight controller directly, but we can’t responsibly make that the recommended configuration.

If I take the 2 pin jumper off, does the dedicated supply the go to pins 2 and 4 (top left pins)? Does the power coming from the 6 pin cable get overridden or do I need to remove the power pin? If so, do I remove the ground pin or leave it grounded to Pixhawk? If you could take a pic of it that would be great.

@proficnc I already have the jdrones product, so I would like to use what I have. Could I alternatively use the external power pinholes on the jdrones connector board? Then would I disconnect the power wires to the Pixhawk? Leave the ground to Pixhawk?

Brownouts with Pixhawk2?

Original Pixhawk if I remember correctly. Was a long time ago.

Pin 2 is ground and 4 is +5. 6 pin cable is fine as it is because if you were powering the 900 from it you would be jumping pin 6 to 4 for power. Just take the jumper off and power from a +5 BEC to pins 2 and 4.


Excellent! Thank you very much!

I’ve had strange PixHawk behavior (on a clone PixHawk) before I brought in a separate power feed to my RFD900x. Let me amplify the warning.

Since the RFD900x can dynamically adjust transmit power, it can increase and decrease the amount of power that it is consuming. This will tend to happen as the range between TX and RX increases. It won’t happen when you’re testing on the ground with both the TX and RX turned on. So, this sort of failure can be fairly intermittent and insidious.

I believe that the one thing that saved me is that the RFD900x in the plane will use a lot of transmit power if the ground side radio is turned off, causing the brownout. If I had always powered my ground side radio first and quickly established a good link with the plane, I doubt that a brownout would have been seen while the plane was on the ground.

A separate power feed is important if you want to use the full transmit power of the RFD900x. If you do not have a separate power feed, I strongly suggest setting the RFD to a lower level of maximum power.

new to RFD, i have the plus version like yourself, i am slightly confused about how to power the bec for it, should i solder the bec wires to the esc main lead or the battery lead, any pictures would be greatly appreciated

Power it with a dedicated 5 volt power source. power the BEC directly off the power source.

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This is the very helpful video I used to power my RFD900x

thanks for the reply friend