Second Receiver with Spektrum Satellite Antenna

Hi all,

I’ve got a Pixhawk4 with The Cube, and am trying to setup a second receiver an addition to a Spektrum Satellite antenna plugged into the SPKT port. My second receiver is an RFD900 (connected to RCIN) passing through a PPM signal originating from a Spektrum Receiver feeding the 900mHz ground transmitter.

However, it appears that Pixhawk only recognizes one or the other input? I can establish connectivity and control through the 900mHz link only, and the Spektrum Satellite only, but not together. I’ve tried setting bit 10 in RC_OPTION (allow multiple receivers) with no success.

No matter what I do, it will not revert between the two when the other is lost…making me think that the SPKT input is treated decidedly different from RCIN with multiple receivers.

Any thoughts? Thanks!

According to the wiki, Plane will use whichever it sees first. It will only switch when the first signal is lost. So it will only use one at a time, even when both are connected.

One thing I’d be careful with is that Spektrum and RFD900 may have different values. So centre stick, or full travel on one system may not transmit as the same on the other. I’m not sure how your radios are set up (if you’re using one radio or two) but you should double check that when each radio is connected the Cube is seeing the same values.


Thanks for the reply. My point is that the SPKT port isn’t behaving like the wiki suggests that it should. It does not switch when the first signal is lost.

Thanks for the additional pointers. I am using one transmitter with two “paths” to the airplane, if you will. The values between the two paths are not exact, but are close enough that behavior and function are unimpeded.


The thought just occurred to me that the SPKT and RCIn might be the same serial port in the end (just with different inverters and voltage pins). Try setting up the RDF900 on one of the other serial ports like GPS2 or TELEM2. Remember to set SERIALx_PROTOCOL to 23.

Good thought! And I will try that when I get a chance.

I realized, however, than an additional confounding variable is the failsafe state of the ground transmitter equipment - it may be giving the aircraft false information in the form of last known command. I need to check that as well.