Using XCTU, everything seems to work fine on the two newly purchased XBee-PRO 868 modules.
Trying to discover any of them from the other does not work, however.
The documentation does not provide much help either. It gives the impression that it’s just to hook everything up and it’ll work.
I have tried the default network ID and a custom one (the same on both units of course).
I have tried to have both as routers.
I have tried to have one as router and one as coordinator and doing the discovery from the coordinator.
I have tried max TX power and min TX power (the same on both units).
I have tried broadcast destination address and the unique destination address (of the other unit of course).
I have set node-discovery options to 7 and 0.
The result: Nothing!
(Well, the associate pin blinks which seems to be the signal of everything being fine. When setting the module to cyclic sleep, the associate went from off to blink in accordance with the sleep and wake cycles.)
With a SDR dongle, I have concluded that both modules are transmitting. There is a slight, but obvious difference in the transmitting, however.
First of all, there is pilot(?) tone at 868.74915MHz on one of them whereas it is found at 868.74935MHz on the other. A difference in about 200Hz. Is this enough to lose sync between them?
At around 869.137MHZ there is a “background” transmission going on but, again, there is a difference of about 200Hz in absolute frequency.
When feeding data to the modules, a much more powerful transmission is sent with a power peak at around 869.476MHz, again, with a slight difference in frequency.
So, since both modules obviously have working radios, why can’t they discover each other?
Is it the reception that’s broken somehow?
Adding another test, no, the reception works. Hooking up the modules with one of them in spectrum-analysis mode and the other getting serial input (thus transmitting as known from the previous tests), the received signal idles around -110dBm to -120dBm when serial input is inactive and -60dBm when active. Swapping the roles gives the same result.
So, the modules are capable of both transmitting and receiving RF energy but not capable of hooking up. Why? What’s going on here?
These gizmos are really powerful! The document note on “least 1m apart” is an understatement. With them hooked up to the same computer, spreading them out on a large table wasn’t enough.
Not until I put one of the units under the table, everything was discovering as expected.