I did the test again, this time logging serial on the node. At 4277 and 4280 you see how the messages fail the first time. It is expected since the GW is down. Then I start the GW. There is no attempt to connect on the node's side. After one hour you can see how the node fails to send messages, this time the GW is up. The node does not seem to register during this hour. When I restart the node, the connection to the GW is established as it should. Maybe it is a bug?

0 MCO:BGN:INIT NODE,CP=RNNNA--,VER=2.1.1
3 TSM:INIT
4 TSF:WUR:MS=3000
11 TSM:INIT:TSP OK
13 TSM:INIT:STATID=2
15 TSF:SID:OK,ID=2
17 TSM:FPAR
53 TSF:MSG:SEND,2-2-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
2060 !TSM:FPAR:NO REPLY
2062 TSM:FPAR
2098 TSF:MSG:SEND,2-2-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
3006 MCO:BGN:STP
3135 MCO:BGN:INIT OK,TSP=0
4277 !MCO:SND:NODE NOT REG
4280 !MCO:SND:NODE NOT REG
3604282 !TSM:FPAR:NO REPLY
3604285 TSM:FPAR
3604322 TSF:MSG:SEND,2-2-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
3604328 TSF:MSG:READ,0-0-255,s=255,c=3,t=20,pt=0,l=0,sg=0:
3604334 TSF:MSG:BC
3605475 !MCO:SND:NODE NOT REG
3605477 !MCO:SND:NODE NOT REG
0 MCO:BGN:INIT NODE,CP=RNNNA--,VER=2.1.1
3 TSM:INIT
4 TSF:WUR:MS=3000
11 TSM:INIT:TSP OK
13 TSM:INIT:STATID=2
15 TSF:SID:OK,ID=2
17 TSM:FPAR
53 TSF:MSG:SEND,2-2-255-255,s=255,c=3,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
814 TSF:MSG:READ,0-0-2,s=255,c=3,t=8,pt=1,l=1,sg=0:0
819 TSF:MSG:FPAR OK,ID=0,D=1
2060 TSM:FPAR:OK
2061 TSM:ID
2062 TSM:ID:OK
2064 TSM:UPL
2067 TSF:MSG:SEND,2-2-0-0,s=255,c=3,t=24,pt=1,l=1,sg=0,ft=0,st=OK:1
2076 TSF:MSG:READ,0-0-2,s=255,c=3,t=25,pt=1,l=1,sg=0:1
2081 TSF:MSG:PONG RECV,HP=1
2084 TSM:UPL:OK
2085 TSM:READY:ID=2,PAR=0,DIS=1
2091 TSF:MSG:SEND,2-2-0-0,s=255,c=3,t=15,pt=6,l=2,sg=0,ft=0,st=OK:0100
2097 TSF:MSG:READ,0-0-2,s=255,c=3,t=15,pt=6,l=2,sg=0:0100
2105 TSF:MSG:SEND,2-2-0-0,s=255,c=0,t=17,pt=0,l=5,sg=0,ft=0,st=OK:2.1.1
2113 TSF:MSG:SEND,2-2-0-0,s=255,c=3,t=6,pt=1,l=1,sg=0,ft=0,st=OK:0
2139 TSF:MSG:READ,0-0-2,s=255,c=3,t=6,pt=0,l=1,sg=0:M
2146 TSF:MSG:SEND,2-2-0-0,s=255,c=3,t=11,pt=0,l=12,sg=0,ft=0,st=OK:GardenMaster
2156 TSF:MSG:SEND,2-2-0-0,s=255,c=3,t=12,pt=0,l=3,sg=0,ft=0,st=OK:2.0
2164 TSF:MSG:SEND,2-2-0-0,s=1,c=0,t=7,pt=0,l=0,sg=0,ft=0,st=OK:
2171 TSF:MSG:SEND,2-2-0-0,s=2,c=0,t=6,pt=0,l=0,sg=0,ft=0,st=OK:
2178 MCO:REG:REQ
2181 TSF:MSG:SEND,2-2-0-0,s=255,c=3,t=26,pt=1,l=1,sg=0,ft=0,st=OK:2
2188 TSF:MSG:READ,0-0-2,s=255,c=3,t=27,pt=1,l=1,sg=0:1
2193 MCO:PIM:NODE REG=1
2195 MCO:BGN:STP
2323 MCO:BGN:INIT OK,TSP=1
3467 TSF:MSG:SEND,2-2-0-0,s=1,c=1,t=1,pt=2,l=2,sg=0,ft=0,st=OK:96
3475 TSF:MSG:SEND,2-2-0-0,s=2,c=1,t=0,pt=2,l=2,sg=0,ft=0,st=OK:24

I had a (seemingly) similar issue with my NRF24+LNA+PA board. The solution was stupid simple - just get the node further away from the GW. Or remove antenna if you have one. We usually develop the node connected to the same PC, both GW and the node. It is simply too strong a signal.

@gohan said in nRF24 would not transmit when connected to Nano, but works fine with Mega:

voltage regulators usually can not keep up

LP2985 on Mega gives 150mA, which is at least in double excess of the highest nRF24 +LNA+PA can consume. It should do fine without the cap.

On Nano it is not a voltage regulator. FTDI chip converts serial to USB. And for Nano I did use the caps 4, 10 and 20 uF - none helped. Honestly, I haven't noticed any effect of these caps so many on the forum talk about. If it works, it works, if not - bad luck. I can believe in a very rare case the extra charge of a 20uF cap could topple the scale, giving illusion that this is a solution.

When I reduced from RF24_PA_MAX to RF24_PA_HIGH it started to work sometimes. When down to RF24_PA_LOW it works stable. However I transmit 7 bytes only, the payload can be up to 32 bytes. This will further increase power requirements and will further short 3V3 output.

In order to save MySensors lib from ungrounded suspicions (which I had) and simply to act professionally we should admit that on Nano the 3V3 output should not be used. Otherwise the behavior is undefined. Even without PA. The spec for nRF24 says 14mA at transmission. The spec for FTDI says it 15mA typical, 24mA max. It is an unacceptable low margin for expecting stable communication.