Hello! 🙂

If you are reading this then hopefully you are a lucky owner of a Unit 3 Compliance Pocket EMC Debug Probe and love it so much it goes everywhere with you, in your toolkit, on your keyring, or in your shirt pocket. Dazzle your colleagues*, impress your manager and baffle your children by knowing exactly what to do with it.

* Note: Colleague be-dazzlement is not guaranteed. Some assembly required. May contain nuts.

How To Use It

To help you debug EMC problems like a pro, we’ve created a guide all about Near Field Probing.

The theory of how these probes work, which ones to use, when to use them, and some case studies showing problems we have solved with their assistance.

>> You can download our free eBook on Near Field Probing here <<

V2 pocket EMC debug probe PCB - near field probe set - board rear
V2 pocket EMC debug probe PCB - near field probe set - board front

Assembly Guide

Components required:

0805 resistors

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

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.

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.

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.

Ferrite cores for 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.

Accessories

RF Cable

I like using RG-316 coaxial cable for probing applications because it is thin and flexible. The last thing you want is a thick, stiff cable when you are probing fine pitch surface mount devices.

You can source this from normal distribution channels like RS but I usually pick mine up from eBay for fraction of the price.

For this kind of comparative application, a couple of extra dB of loss in cable from a cheap part is neither here nor there.

RF Adaptors

Don’t forget to pick up a coaxial adaptor or appropriate cable if your spectrum analyser doesn’t have an SMA input. SMA to N and SMA to BNC will be readily available.