hi,all,
I use routerboard 532a r5 ,r52 ,one 15dBi Omni Antenna, outside box,configured as AP B/G ,I installed it at roof,my house is bungalow ,but I only got 18Mbs speed,I don't think so it will be such slow,
is any one known why?
thank!

Might be because an omni has a beam pattern like a "donut". You will always get bad signal if located BELOW an omni, because omnis (if not tilted, which I would consider a really strange setup) will transmit/listen in (more or less) a "plane" around them.

Apart from that, there are several others factors that could come into play.
For example: What's the material of you roof? Does is let RF through?

With your setup (hig gain omni on the roof-top) I would suspect that you will/could serve internet to lots of your neighbours quite well, but probably not for yourself

Best regards,
Christian Meis

When you say only getting 18 Mbps speed, are you referring to the air data rate, or are you getting 18 Mbps (TCP/UDP) true throughput using a bandwidth test, or a file transfer, etc.?

The reason I ask is because if your getting 18 Mbps true throughput then that is the best you can hope for in that configuration, and is a pretty good result.

I'm not doing any test ,I think I'm talking about signal strength

If you have your data rates left at 'default' setting, RouterOS will pick the data rate that corresponds with the amount of traffic passing on the link.

If its connected with 802.11g, you will see 6, 9, 12, 18, 24, 36, 48, 54 Mbps as possibilities.
If you are just connected and not really doing anything, then the date rate will most likely read 6-18 Mbps, once you start passing traffic it should go to the higher data rates (providing the signal is good enough and there isn't anything interfering).

You can also 'lock' in data rates and test to find out what it can and can't do reliably. But remember to actually see the usage of the higher date rates you need to pass enough traffic over the link to make it use that rate.

Cheers