Signal issue with RB800 and 802.11N wireless card

RouterOS Wireless Networking
1

Hi guys!

I’m using for the first time 802.11N wireless card on a RB800 (I’ve never used 802.11N card neither RB800 for other purpose).
Routerboard: 800
Wireless card: Atheros 11N
Firmware: 5.6

This is the issue:

I’ve a link with two of these radios, distance 1,9 Km, frequency 5Ghz, parabolic antennas 6° 28dBi on both side.

During alignment I’ve set tx-power=10 (all rates fixed).

Calculation said a received signal of -49 dBm. I’ve rached -50 dBm, so satisfied :slight_smile:

Now, due to regulatory, I must decrease tx power to 3 dBm but if I do this received signal drop to -69 instead -57 as I expected…
The signal is the same on both side.

Trying other values between 3 and 10 I see a non-linear change in received signal. It seems to be a threshold. Above it, calculation and mesured signal match. Under it, they are very far.

What’s wrong?

Radios don’t trasmit the power I’ve set?
Radios don’t measure correct received signal? (Algorithm problem?)
Am I wrong?

Unfortunately I’m installing other link at the same time and they the same issue.

I’ve read http://forum.mikrotik.com/t/insane-ht-signal-strengths-running-station-bridge-ros-5-6/49911/1 where uldis says that too low power is not good. Could you confirm this? If yes how can use low power?

Thank you for all your work!

Andrea

2

Does anyone know the answer?

3

when using very low tx-power on high power wireless cards the lowe tx-power settings might not be so linear. So in your case I would suggest to use antenna with smaller gain so you would not need to lower the tx-power so much.

4

Thanks for the aswer!

Could you say me which power range N card is designed for?

5

each cards manufacturer could have different values. I think it could be from 10db and above.