WLAN professionals all know the importance of measuring and confirming attenuation levels when doing a predictive site survey. However, sometimes it is simply not easy to place your RF generating device in a stable location. Do I place it on a table or chair? Can I raise the AP “just another foot” so I can get an accurate measurement? And when I need to place it in a good location, where can I place the AP (and it’s power supply) so that I can get an accurate measurement? I have had the same problems when I have been on site to do attenuation checks. So, head out to the garage with me so we can together “engineer” a tool to hold an AP for attenuation measurements!
Well, you can see there is not any real “high-tech” in this engineering prototype. We have a piece of Plexiglas, some hardware, a camera stand and of course, the AP and power supply. But it does do the job we need to allow us to locate the AP in all the right places. So simply speaking, here is what I did. (I’m not going into the details of how to do wall attenuation measurements, as there are already some great blogs on this topic. They are all listed below.)
- Obtain any camera stand/tripod. I had an old Kodak stand in my closet at home, max height is 52 inches (1.32 m). Any stand should do, or you could even use a Manfrotto stand from your APoaS mount. However, remember that your mount needs to be flexible and easy to move, as you will be quickly moving in and around offices, tables, cabinets, etc. So, a camera stand that is fast to setup and tear down is important.
- I picked up a small piece of 1/4 inch Plexiglas at a local glass supply shop and put a hole in the middle and epoxied in a 1/4-20 nut. (check out your camera stand top mount screw and get a nut with the same thread size). I then drilled two other holes as a strain relief for the power cord for the AP.
- Velcro to the rescue! I used it to attach the AP to the Plexiglas mount and the power supply to the camera stand leg. (I used my Ravpower power supply–details below)
- I used a ten foot USB cable extension for the power cord to the AP (details below).
So, that’s it! A stand to make your RF attenuation measurements fast and easy! Below is the parts list and some additional pictures. And as always, gcatewifi wants to know your reactions, comments and suggestions. Use the “Leave a Reply” box below to do just that!
- 6″ x 3″ (15.24 cm x 7.62 cm) piece of 1/4″ (6.4 mm) Plexiglas
- 1 – 1/4-20 nut (get the nut that matches the thread size of your camera stand)
- Camera stand (of your choice)
- 1 – 10′ (3 m) USB 3.0 extension cable (Cable Matters 200008-Black-10)
- TP-Link AC750 Wireless Travel Router (TL-WR902AC). Of course, you can use any small RF generating device, even an AP in autonomous mode. However a “travel router” is lightweight, easy to connect/configure and uses low power. Personally, I disable the 2.4 GHz channel, and select a 5 GHz channel that is not used much, with low power setting on the AP. Links below seem to agree that using the 5 GHz band will help you to obtain more accurate RF attenuation levels.
- Ravpower power supply RP-PB14. (this model may not be available, but there are plenty others here.)
Also, be sure to check out these blogs which help detail even more on how to measure RF attenuation levels:
- RF Attenuation Measurements (WLPC 2015-Berlin) by Ferny Muñoz
- Wi-Fi Planning, Walls and dB’s – Measuring Obstruction Losses For WLAN Predictive Modelling (Ekahau blog) by Nigel Bowden
- Measuring and Annotating Wall Attenuation for Predictive RF Site Surveys by Devin Akin