Migs,
Do you know if Italy has the same regulations for CB frequencies as does the UK. If the rules are EU wide I might have at least a suggestion that would account for what you're experiencing. The UK uses the same number of CB channels and the same frequencies for CB that are allocated in the US. But one is FM and one is AM. So there are completely NOT interchangeable.
If you got US radios on your new bikes this would account for them being able to transmit and receive with each other but not with any other radio that used the other modulation. From the rider's perspective they would look the same, feel the same and act the same since you'd be scrolling through the same number of channels on the same frequencies. But you wouldn't "hear" anyone else.
Just a guess. Would hate to think that Harley made a mistake like that. But it fits your current facts.
That sounds VERY logical to me Twolane! One thing that's different about the Harman/Kardon sets is that - unlike the Radiosound ones - they are all the same, and the firmware is simply changed to regionalise them; if they forgot to set to Euro frequencies/FM for the CB on a batch that left the factory bound for Italy, your explanation is bang on!
Yes, the FM CB frequencies here in the UK are Europe wide, I think. Not the same as the US ones though, if I remember correctly; they are still in the 27MHz band, but slightly higher up (with some ovelap, on the higher channel numbers, I think).
Jim