Will it work? (2x2 MIMO antenna on 3x3MIMO RB)

gregoro · Mon Apr 06, 2015 10:53 pm

Greetings.
My next project includes the use of NetMetall 5 for a longer point-to-point connection. There are two types of NetMetall 5 (2x2 MIMO and 3x3 MIMO), so my question is as follows: Can I use RB921UAGS-5SHPacT-NM and connect it to the MTAD-5G-30D3-PA in the 2x2 MIMO configuration so that only two chains would work? The third chain would remain disconnected. I know that I wouldn't achieve full speed but that's currently not the issue. When the 3x3 MIMO antenna (maybe from Mikrotik) becomes more commercially available I plan to replace MTAD-5G-30D3-PA with that one and then all the chains would be used.
Thanks in advance

InoX · Tue Apr 07, 2015 1:07 am

Yes you may.
From my tests, 3 chains worked worse than 2 chain on netmetal. I used one 2x2 antenna and one panel. So now I have connected only 2 chains and disabled the third.

IntrusDave · Tue Apr 07, 2015 6:32 am

if I understand correctly, you are asking if you can use a 2x2 antenna on a 3x3 radio.
The simple answer is no. Each transmitter MUST have an antenna. If not, you will burn out the radio, and likely cause RF issues inside the unit.

However, *IF* you can completely disable the radio that does not have an antenna, and insure that it stays off, then you may be okay.

Tue Apr 07, 2015 7:00 am

Do you want to say that even the chain is disabled the amplifier is under power and gets input signal so without load on the output it will burn? I don't agree with this.

IntrusDave · Tue Apr 07, 2015 7:05 am

Do you want to say that even the chain is disabled the amplifier is under power and gets input signal so without load on the output it will burn? I don't agree with this.

I did not say that, and for a reason. Because I do not know what radio he is using or the design of the board and the firmware running it. Without being able to the code behind the scenes, I do not know if the amp is disabled when the radio is disabled. I also don't know if it is a simple 3-channel amp, or if it's 3 independent amps.

So, the only "save" answer is to attach an antenna. Even if it's just a little Dipole pigtail, it's better than risking a radio burning out in the field.

Tue Apr 07, 2015 7:10 am

Ok. A shielded resistor terminator could be good for security. But when tx on any chain is switched off, it doesn't transmit.

gregoro · Tue Apr 07, 2015 1:35 pm

So if I understand correctly, I can use the above configuration if I (just in case) provide protection for the 3rd chain?
Because looking at the ETH/POE port, the label says "Do not power on without antenna connected!" Does this mean I have to attach three antennas, turn the device on and then disable the 3rd chain?

Tue Apr 07, 2015 2:31 pm

Exactly.

Morpheus1607 · Tue Apr 07, 2015 4:16 pm

we have the 3x3 Mimo Netmetal with 2 chains and its still no Problem. Just disable the 3rd Chain at 1st Installation an all will be fine.

czolo · Fri Apr 10, 2015 2:15 pm

Or jutst disable TX on third chain.