Monday, April 25, 2011

My magnetic survey rig

This is my site survey rig.  Most of it came from the shelves of our local Ace True Value hardware store.  After some trial and error, I came up with the solution that works for me. 

The flexible painter's handle was probably the most difficult thing to find - I shopped around for weeks until I found "the perfect" one.  I wanted something that was flexible, and wanted to minimize the RF attenuation cause by the metal.  So I chose the metal flexible handle and a fiberglass painter's pole.

I wanted to make something that I could use by myself - so I bought a "rare earth magnet" on eBay and taped it to the flexible portion of my survey pole.  This allows me to walk up to any metal ceiling grid and have my survey pole stand up by itself while I do my thing.  Turns out one magnet was making me uncomfortable, so I taped another on there and both of them side by side definately do the trick.  Just enough to hold it there, but not enough to pull down the entire ceiling.  Your mileage may very.

Cisco 1252 with ceiling mounted antennas

Sometimes you never know what you're going to find...

Saturday, April 16, 2011

CUWN power levels and the 5GHz channels in the U-NII band

This is something that I have found to be confusing.  The UNII bands in the 5GHz range have different power limits.  They are as follows:
  • U-NII Low (U-NII-1): 5.15-5.25 GHz.  Power limited to 50mW
  • U-NII Mid (U-NII-2): 5.25-5.35 GHz.  Power level limited to 250 mW.  Subject to Dynamic Frequency Selection (DFS, or radar avoidance)
  • U-NII Extended 5.47-5.725 GHz.  Power limited to 250mW.  Subject to Dynamic Frequency Selection (DFS, or radar avoidance)
  • U-NII Upper (U-NII-3): 5.725 to 5.825 GHz. Power limited to 1 watt.
If you are a WLAN Engineer like me and you happen to use WCS, your power settings will be displayed as a number, 1 - 8, not in a dBm value.  The value of 1 is the highest power, and the value of 2 is 3dB lower than the value of 1, value of 3 is 3dB lower than the value of 2, and so forth.  Each 3dB is half the power of the the previous value.  Since the cell size is halved every 6 dB, an AP with a power level of 1 should have a cell twice the size of an AP with a power level of 3.

What if you have have a dozen APs all with a power level of 1 set via RRM?  If the AP's channels are dispersed throughout the U-NII low, mid, extended and upper bands, then theoretically the max outputs could be anywhere between 50mW to 1 Watt.

I would love a table or chart that displays the power settings and dBm values for all the model numbers under the CUWN product line.  Heck, if I ever have the time, maybe I will write it up and post it for y'all to reference.