Indeed, the documentation included with the hardware does mention to attach both antennae as otherwise the device will fail to operate. So, I dutifully followed the instructions and attached both antennae and turned on power .. to be disappointed with no 3G/4G LED turning on and no signal LEDs turning on! I was about to give up, thinking I was too far from the mobile tower when I decided to remove the antennae. So, I removed the first antenna. No change in status. I proceeded to remove the second one and while I was unscrewing the antenna I noticed the 3G/4G LED turn on, followed by two signal LEDs! Not sure what happened there but, hey, I am just a customer! I then re-attached both antennae as before and the 3G/4G LEDs and one or more of the signal LEDs remained on and what was more, I was connected! What was even more incredible, speed tests showed that I had a download speed close to the promised 20Mpbs even with weak signal levels!!
On a side note, I noticed that when my first NBN modem was installed, the installer used an attenuator between the wall socket and the NBN modem. Some time back I received a new NBN modem with instructions to replace the old one. So, I removed everything, including the attenuator and replaced the old NBN modem with the new and used new cables provided. Unfortunately, the new NBN modem failed to connect and after replacing the new cable with the old cable AND its attenuator, things worked again.
I guess that the moral of the story is, sometimes the signal can be too strong ... and in the case of the wireless service, if there is a strong signal from the mobile tower, attaching the antennae may result in a signal that is too strong for the sensitive RF circuits...
