nRF24L01 with Nano, strange on external power

Hello everyone!

I'm trying to setup a battery powered Nano to send data to an Uno using nRF24L01+

I am using maniacbugs RF24 lib.

I am sending a packet from my nano to the station, let it send it back to my nano, compare the two data packets and when they are the same, I continue. If not, I try to resend the packet upto 10 times (the autoack function and CRC does not always manage to successfully transmit in one attempt).

This is all working as long as I a) power the nano thru USB or b) power it using an external 5V supply that feeds VIn. When I instead use a 7,4V LiIon pack on VIn, I dont manage to get successful transmits anymore.

The Nano still sends it's data and the Uno receives it. Then the Uno sends it back to the Nano, but the Uno does this always 10 times, so the Nano must think it doesnt successfully receive the same data that it sends.

Hooking up a LCD to the Nano, I test where it breaks. It is the radio.write() that always fails (even tho the Uno does receive data of course).

Any ideas what I can try to troubleshoot?

Thank you and a nice weekend to everyone!

RURon.

Please upload the wiring. Anyways you have to connect the ground and v+ from external source.