RB751 - wireless chain0 and chain1 usage clarification

RouterOS Beginner Basics
1

Hi all,

I read the Mikrotik documentation about RB751 (http://routerboard.com/pdf/357/rb751U-2HnD-ug.pdf) and I’ve many doubts about the wireless section:

Wireless device
RB751U includes a 2GHz 802.11b/g/n wireless device built in. It has PIF type antennas (2.5dBi) built into the case, and one MMCX connector for an optional external antenna.

RB 751U has 3 built-in wireless antennas

• Chain0
o one antenna for TX
o one antenna for RX

• Chain1
o one antenna for TX/RX
o MMCX connector for external antenna

To enable the external MMCX connector, set “antenna mode: antenna-b” in RouterOS wireless settings, in the HT tab of Winbox. Note: enabling the external antenna disables the built-in Chain1 antenna.

I’m not able to understand when it’s convenient to enable/disable Chain1 on RB751 to improve network speed.
Why should I enable chain1 when TX e RX data are shared on the same single antenna?

Let’s me more specific about my doubts. For example if I use a RB751 as simple hotspot do I need to enable chain1 to improve network speed?

I have a different scenario in my mind:

clients —> RB751-1 <wifi bridge> RB751-2 <**** wifi bridge ***> RB751-3 ← clients

Probably on RB751-1 and RB751-3 chain1 has to be disabled and on RB751-2 chain1 has to be enabled. I’m right?
I believe that, in this scenario, RB751-2 isn’t the best choice because it has only 3 and not 4 antennas. Do I need a true 2x2 MIMO device in this case? Any suggestion?


Thank you.

2

You never need to disable any chains to improve anything. This is only for the situation, when you want to add the external antenna. If you don’t want that, do not disable any chains.

3

Sorry normis but I need further clarification:

If I enable chain1 the third internal (or MMCX external) antenna will be active: is it righ?
If yes, is the third antenna an improvment for my clients?

Best regards.