Pocket Near Field Probe Boards (R4)

Hello and welcome to Unit 3 Compliance.

We test your products for EMC and Electrical Safety, and fix them if they don’t pass.

We also provide customised EMC training via Think EMC.

If you have picked up one of our new Pocket Near Field Probe kits from us then, oh my goodness, we hope you like it as it is one of our best yet. We’ve added cool new features and some useful EMC reference formulae as well as the near field tools from the original.

Download our Guide

But first things first – if you are new to Near Field Probing then you simply must check out our free eBook that has everything you needed to know (and probably a lot that you didn’t) about the art of near field probing to help solve EMC problems.

* Click here to download it *


What’s In This Probe?

Get started assembling by snapping off the two parts shown.

The first part is our contact details and, on the back, a quick reference of useful EMC formulae.

The bit from the top is a new addition: an SMA spanner (careful with that torque Eugene) and a key for opening Wurth Elektronik snap on ferrite cores.

You can then assemble the rest as described below.


Assembly Guide

Components required:

0805 resistors (10:1 voltage probe)

R1 = 470R and R2 = 10k, gives a 450 ohm parallel combination. This is required for the 10:1 divider into a 50 ohm input.

0805 capacitor (10:1 voltage probe)

C1 = 220pF to 2.2nF, C0G/NPO dielectric, 50V

This AC couples the signal from the probe into the measuring instrument. Many spectrum analysers have a 0VDC requirement on their RF input.

The actual value isn’t too important at the frequencies we are interested in.

Metal pin for contact probe

For the contact probe pin we recommend using a male pin header from a 2.54mm pitch connector strip and filing the end to sharp point with a metal file.

These parts are available from all major component distributors and from eBay again.

We also recommend securing this in place with a generous blob of 2-part epoxy adhesive to provide some additional mechanical strength.

Edge mount RF connectors

The 1.6mm thick PCB is designed to take SMA edge mount female connectors to connect to an SMA-SMA RF cable.

These connectors are available from a wide range of sources but most readily and cheaply from eBay

You can solder a coaxial cable onto the pads at the expense of ease of swapping the connection between probes.

Ferrite cores (current transformer adaptor)

The current transformer adaptor was designed to use the excellent Wurth Elektronik 742715x series of ferrite cores which are available in different sizes.

If you do get one, tie the two-pronged plastic unlocking key to the probe with a bit of string so that you don’t lose it!

An M3 screw and nut will secure the core to the board, but again a blob of two-part epoxy adhesive or some hot melt glue will do the trick.

Experiment with the number of turns but we generally use between 5 and 10 as a starting point.


Finished Product

Here are our probes that we use in the lab for all kinds of EMC problem solving:


And if you really know what you are doing with these probe boards, there’s a secret power user Easter egg mode available.

Tea up!


Mug is from Mike’s Electric Stuff