Blended GPS not showing up in Mission Planner

I have a Pixhawk 1 with copter 3.5.2. I added a second M8n gps to try out the blended gps functionality and I get strange behavior in mission planner. Although the ardupilot wiki indicates that both gps will be visible in MP, I have zero SATs with an HDOP of 99.99. GPS 1 is on serial 3 and the 2nd GPS is on serial 4. Followed the wiki instructions regarding settings. Another issue, when I enable the GPS on serial 4, the telemetry radios cease to function (serial 1). Has anyone else seen any of these issues?

I am having about the same problem with copter 3.5.3. I followed the steps in the copter documentation, looked at the blog and wiki. I have hdop2=99.99, no satellites are being seen by the second gps. The only thing I have not done is switch them around to make sure they second one actually works. I am using a Pixhawk 2.4.8 with two ublox m8n gps receivers.

It should work so I think it’s most likely a configuration issue.

I think checking all the SERIALx_PROTOCOL and SERIALx_BAUD values is a good idea. Make sure that the protocol is set to “3” (for GPS) for only the two ports where GPSs are connected. The baud should be 57 or 115 although getting it right is a little less important because if you get it wrong the GPS driver should search though all the possible baud rates until it finds one that works.

Thanks, I just checked those and all seems good. I switched ports for the GPS and the problem moved from GPS2 to GPS1. Some further checking leads me to believe that I received a bad NEO-M8N GPS unit from the ebay seller I bought the Pixhawk kit from. I have contacted him about a replacement GPS unit and in the mean time I ordered another on from another seller. I just replaced the center plates in the F450 I have been flying with the SPYDA 500 plates. They both use the same arms so the change was quite easy, That gave me more room for the Pixhawk and a gimbal controller so I can add a Gopro clone action camera.