Sunday 13 March 2016

Espressif ESP-12e module radiation pattern

The ESP-12e module has an onboard PCB antenna. When an IoT device is located near the edge of my WIFI network, pointing the antenna the right way may add a few meters to the useable range.
Having had a little time over the weekend, I decided to build a contraption that allows me to rotate the module and record both signal strength and orientation.
There ist a nice protractor.svg file on wikipedia. I use Inkscape to scale and print that.

You may also want to watch my video on this topic here.

Some woodworking

And the protractor
Pointer and tripod adapter
Next I need to put the ESP-12e module in AP-Mode, so it sends beacon packets. Then I wire it in a very basic configuration to run from a 3,7V lithium cell. To drop 0.6V, I put a 1N4148 in series with the module. (Actually, a 1N4148 a bit weak for the job. Go for a 1N4001 if you can. I couldn't find one in my parts bin.)
The TXD/RXD wires are still connected for programming
Can it get any simpler than that? GND and GPIO15 are connected to the negative terminal, VCC and CH_PD to the cathode of the 1N diode. The anode is connected to the positive terminal.
I use a 18650 cell and this holder.
No more unnecessary stuff
Test run
Now mount it all on a tripod and wait for a sunny day to take it all outside where we have little or no reflections.

Ok, let's go outside...


I used LibreOffice to turn the handwritten values into a polar diagram. Here is the resulting  chart:

Although I didn't expect the field to be completely uniform, the result is pretty obvious:
The module (looked at from the component side, antenna pointing away from us) has a clear west-north-westernly preference and a clearly visible minimum at the opposite end. So you'll want that (upper left) corner of the module to point at your access point if you get near the edge of your wifi range.


While working on this project, I found out about the ESP-12F, which supposedly has an improved antenna design over the ESP-12E. I do not have one here at the moment, but will compare the two if I can get hold of one.
To get a smoother chart, I should do two full rounds to smooth out the errors and do finer steps (5 instead of 10 degrees).


If you want to try the same, you don't need a Wifi tester. A PC with InSSIDer (the free version), or even use another ESP-Module as WiFi scanner as shown here.

PPS: Shopping list:

Thin plywood, the size if an A4 paper
The protractor.svg file from wikipedia
A 18650 rechargeable battery. (Well, and a charger if you don't have one)
Suitable 18560 battery holder
One 1N4001 diode
and of course the ESP-12e module

1 comment:

  1. Excellent Andreas! Now I know where to point it ( north west ). What would also be useful is to know what happens if the ESP12 is pointing transversal to the AP ( up or down ), but if this is the best option, I will go for it !