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Adding a Reflector to the MP-01

Author: Elektra


Background

This article describes a simple reflector for the Mesh Potato MP-01 to produce a more directional radiation pattern than the normal patter which is essentially omni-directional.

A flat reflector behind a monopole or dipole antenna offers a gain of 4-6dB, depending on the distance between radiating element and the reflector and its size.

The MP is tricky with this regard, since there are two monopole antennas etched on the pcb side by side. To make things more complex, they are quite close to each other and connected to circuitry (while the left antenna is transmitting, the right antenna receives a small part of the energy and feeds it into its receiver circuitry)

Hence the MP antenna system does not behave like a perfectly evenly radiating omnidirectional antenna, but more like a complex two element monopole array.

To make a long story short, with the reflector mounted to the MP, I have found the main radiation beam is aiming ~45 degrees to the left like this:

 \
  \ main radiation beam
   \
    \
     \
   [_____]    mp
 ------------ reflector
      O       pole


I expect that you can double the distance between two MPs with the reflector. The reflector doesn't add an awful lot of gain, expect around 3-4dB. The beamwidth is relatively broad, as the whole antenna system including reflector is not a high gain directional antenna system.

If you need long distance links, you can use the UFL connector socket on the board with a pigtail and a strong omni. You have to remove one resistor and solder a little bridge to switch between internal antenna and UFL port.

I'd recommend Radio-Mobile to do the calculations with topology data of the area where you are planning to deploy the devices.


Material

To construct the reflector the following is required:

190 x 240mm blank aluminium sheet, 1.5mm thick.

You can use material wider than 190mm, if the store sells 200mm wide this is also fine. I recommend to have a professional workshop cut the metal sheet to the outer dimensions. The store where you buy it might do this. They have the tools to easily cut it to a straight form. I did it by hand, it doesn't look perfectly straight. Doesn't matter for the function, though.


Tools Required

Drilling machine (box column drill preferably, as a hand-held drill tends to slide over the metal, so holes might end up not positioned accurately)

White paint

Alcohol as solvent to remove grease from the surface and some old cloth

Cable ties

Some means to cut metal sheet (I bought a metal scissor, but working with 1.5mm aluminium sheet is quite hard)

Four 5x10mm rivets

Rivet pliers

Centre punch

Hammer

A small file

5.1mm drill for metal (for the 5mm rivets)

4 mm drill

Two pieces of flat metal to construct the support brackets

Cutter

Double sided tape (goes between the MP and the reflector)

Optional:

Coping saw with metal saw blade (makes it easier to work out the 4x10mm holes)

Hose clips (instead of cable ties for the pole mount)


Process

I printed the plan on A4 paper and went into the copy shop to copy it on transparent foil, then used the cutter to cut the outer shape out of the foil. I fixed the foil on the metal sheet and marked the lines to cut.

With the cutter I was cutting the 4x10mm holes (for the cable ties) through the foil and into the metal.

With the centre punch and the hammer I marked the location of the holes.

Perform the drilling and cutting.

Work out the 4x10mm holes.

Round the outer corners with the file.

Remove the cutting ridges with the file.

Fix the rear mounting support brackets with the rivets.

Apply the double sided tape between the MP and the reflector.

Carefully attach the MP to the reflector. Make sure the LEDs match with the holes.

The support brackets I used are not ideal, as the end of the rivets are colliding with the pole. But two pieces of foam or rubber (or similar) between bracket and pole would fix this perfectly.


Drawings

 http://download.villagetelco.org/hardware/MP-01_Reflector/mp_antenna_dimensions.pdf
 http://download.villagetelco.org/hardware/MP-01_Reflector/mp_antenna_v2.svg


Artwork

 http://download.villagetelco.org/hardware/MP-01_Reflector/mp_antenna_look.pdf


Pictures

 Reflector-side-view-mail.jpg
 Reflector-view-back-mail.jpg