Routerboard won't use higher data rates

RouterOS Wireless Networking
1

Hello all,

I am having a bit of a problem that I hope someone can help me with. I have a Mikrotik AP (RB 333) and client device (RB 411) which I can connect to each other just fine. My problem is that neither of them will use data rates above 18 Mbps, even though I have the higher rates enabled. My SNR is 30+ which should be more than adequate for the higher rates but it won’t use them. I have even tried to turn off the lower data rates so that it can only use the higher ones but the client device won’t connect to the AP when I do that. Any ideas?

Also, when I try to use any basic rate other than 6 Mbps the client device won’t connect to the AP. Is this a known issue?

Thank you,
Jason

2

I’m using a Mikrotik R52 card and the transmit power is on default. I am also using an RF Linx bi-direcitonal amplifier in both the AP and client device for the increased transmit power and receive sensitivity.

3

Thanks for the info Kijomabb you have been very helpful.

The only problem with eliminating the amp is that I won’t get any receive sensitivitiy enhancement without them. In this case that’s 10db that the amp adds to my SNR. The amplifiers have automatic gain control, would it be benficial for me to turn down the transmit power of the cards to a lower level so the AGC doesn’t attenuate the signal as much? Is the linearity problem on the transmit side or receive side (or both)?

Jason

4

An amplifier does not actually improve SNR. It just amplifies EVERYTHING, adding a little bit of distortion along the way. Doesn’t matter if it’s an audio amp, a cable TV amp, or a 2.4ghz amp, that’s what they do.

Bigger antennas is the way to get not only a stronger signal, but a cleaner one too.

5

Thanks jp, we are using high gain antennas as well but if a receive amplifier doesn’t improve SNR then what is the point of it?

6

To compensate for long cable loss between the high gain antenna and the radio, such as when you receive an adequate signal at the antenna but lose it through the coax.

7

but if the amp doesn’t improve SNR then what good would that do? wouldn’t you just be adding the noise figure as an additional loss?

8

The client/ap will not use the higher dates rates unless they are necessary to use.
Also SNR is not very helpful. I have numerous radio card that report noise floor at better then -105, a signal of -75 would then equate to a 30 SNR but the radio would not use 54 Mbps.
Again there is always the possibility of multipath and numerous or factors that would degrade the signal in such a way the radio would not use the higher data rates in though you think it should.

Past all that get rid of the amps, that is what I would suspect causing the issue, remember they amplify both noise and signal.

Cheers