Saturday, September 20, 2014

WLAN Site Survey Rig - Rev2

I recently decided to rebuild my site survey rig so that it would be able to broken down and put in the back seat of my small commuter car.  In all honesty, I started out trying to rebuild my rig, but ended up starting from scratch.


Searching eBay, I decided on this as my starting point: (it set me back about 90 bucks)


Foldable Table Laptop Cart Workstation Portable Roll Home Couch Office Desk Cart




Next, I decided I needed a round platform at the bottom of the rig to place a small UPS, orange cones, and anything else heavy enough to tip over my cart.  I purchased a piece of ¾ inch plywood and cut it into a round shape, cut a hole in the center, painted it orange (for safety) and screwed it to the legs that the wheels were fastened to.


I drilled a 1.5 inch hole in the upper platform for my painter’s pole.  I quickly discovered that I needed a pipe attached to the base because it was not stable when I attached my flexible painter’s handle with AP attached to the painters pole.  I also drilled and tapped a hole in the pipe so I could insert a thumb screw to tighten down the pole to keep it from spinning on me. 


On my flexible AP mounting arm, I fastened two Rare Earth Magnets that I found on eBay.  I wrapped them with electrical tape around the flexible arm, so when I slid the arm up against a ceiling t-bar, it would magnetically hold the pole steady.  It works beautifully.


After it was all said and done, I assembled the rig and gave it a test drive.  I placed my AP’s power supply in the shelf compartment after lining the shelf with sticky backed Velcro.  That keeps everything from falling out when pushing the rig down a hallway.


Here’s what it looks like:




The entire rig breaks down and fits into the back of my SUV nicely.  The shelf has a handle on it that allows the center support to raise up to desktop height.  The shelf is removable, making the entire rig portable.  Here’s a picture of it all broken down.




Next, I wanted to get the most of my AP’s power supply.  Many of you will recognize this power supply that is made for WLAN site surveying.  I use a Cisco 1140 series AP with the 2.4 GHz radio turned off, and the 5 GHz radio configured for 11 dBm for site surveying.  I wasn’t getting the “full days’ worth of site surveying” out of my power supply, so I decided to do a slight modification.


Here’s my power supply with the stock battery removed.  I decided to finally write down on the front of the power supply how to configure the switches for  charging, surveying, and storing the power supply.  I can’t count the times I have plugged it in to charge overnight and not configured the switches correctly!



I would like to also mention one more thing.  The manual mentions how to store your power supply.  The battery is mounted in the power supply in such a way that it should be stored on its back when not in use.



I wanted to purchase a new battery, and if possible, get a battery that would last a little while longer.  I found this battery on eBay for about 40 bucks.  The advertisement claimed the battery would last longer than conventional batteries.  When it arrived, I noticed the tabs were larger than the initial battery, so I had to use my Dremel tool to modify the tabs to fit onto the new battery.  Here’s what the battery looked like right out of the box.



After modifying the tabs of the new battery, it fit into the power supply perfectly.



I charged my new battery and drained it with my survey AP several times before measuring how long it would last.  After a week, I measured how long it power up my survey AP.  I checked it on the hour, and it lasted over six hours, but was not powered up on the seventh hour.  That said, I now know it will last about six hours of surveying.  I’ve hear that other Engineers get a full day out of surveying with their power supplies.  I would love to hear from you if you have any tips.


Last but not least, I broke the rig down and it fit inside my little commuter car.  Everything now fits in the trunk of my little car, with exception of the pole which fits up front.  That’s a pretty small trunk, and its all in there!