AP1252 20km link test

sorvarit · ‎03-11-2009

Have just done an experiment with connecting 2 AP1252 over a 20km distance with the 5ghz radios (Channel 5745).

Each site are connected with two 26dbi flat panel antennas with 0,5m pigtails on antenna A and B connectors. The C connector are disabled.

The results on the root bridge is:

Current Rate (Mb/sec) 6.

Signal Strength (dBm) -69 Signal to Noise (dBm) 32

The result on the non-root bridge is:

Current Rate (Mb/sec) m0.

Signal Strength (dBm) -68 Signal to Noise (dBm) 32

The terrain is relatively flat so this is not perfect for mimo, but shouldnt the data rates be higher on "plain old" 11a rates?

On the specs for the radio recieive sensitivity is -73dBm @ 54 Mb/s.

jeff.kish · ‎03-11-2009

I take it this is a non-Cisco antenna? I couldn't find such specs on their data sheet:

http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/product_data_sheet09186a008022b11b.html

They have a dish antenna that is 28dBi gain, and it can only manage 54Mbps at 19km. Also, panel antennas aren't as focused as dish antennas. So your performance will be less than this.

Still, 6dBm seems a bit low, but wireless can be unpredictable. If you want to troubleshoot this, you'll need to buy/rent a spectrum analyzer and take it out there to see if there's any interference. You might need to realign the antennas a couple times for optimal connection.

You can also disable the slower data rates one at a time and see whether your bridges can handle the higher bandwidth. Definitely don't put the bridges in production this way, but it at least removes the automatic selection aspect from the equation.

sorvarit · ‎03-11-2009

Ok i tried to disable all mcs rates from 0 to 15 and then the speed popped up to 54mb/s. Are for now satisfied with this and will do some further testing with traffic.

Hope i can use mcs rates above 8, but maybe im too optimistic.

The 26dBi antennas are from MTIWE (MT-486004/N). Have actually a 28dBi dish (not Cisco) connected on connector C, but have not enabled it yet.