Column: Embedded design


Guide to avoiding RF lab accidents


By Myk Dormer, RF Engineer and Director, Smallwireless Limited L


et’s address a very common and annoying lab bench mishaps that happen to hardware under test and the circuits being experimented with.


Leſt on its own, a piece of prototype


hardware is essentially safe from harm; but, the moment you start working with it, or connect it to something, hazard levels begin to rise. For example:


Power supplies No engineer would ever be as foolish as to overvoltage a circuit, or connect a power supply in reverse. Yet, no experienced engineer can honestly say they have never done exactly that – several times! T us: Check supply voltage settings before


wiring up. Don’t just switch on and hope for the best. If a lot of testing at one voltage


is planned (3.3V and 5V aren’t uncommon), invest in a fi xed voltage supply. Set current limits proportionate to the


expected current drain. If possible – and within size limits


– include reverse protection (“idiot”) diodes in the supply rails, or at least in the test jig. Where possible, avoid “crocodile” clips


or hookup probes, and provide a real connector for the power supply. Ensure that your power connector is


not reversible (!). Discharge power supply reservoir


capacitors – with a resistor, not a short circuit – before assuming a board is “safe”.


Physical mountings If you are testing a circuit or a system that is mounted in its own casing with well- behaved connectors, then you are in the happy place. Unfortunately, a lot of devices under test are bare PCBs, and these are always at risk. T us: Be constantly aware of what the PCB is


placed on. Is your bench clean, and swept clear of wire clippings and stray parts? Where possible, mount the board on


standoff s or feet, so it is not in contact with the bench at all. If it needs a heatsink in service, make


sure it gets one when testing it. It most certainly won’t be “just OK for a moment”. Remain absolutely paranoid about


where test cabling goes to and from – especially when you are moving around. Tripping or snagging a cable, and


tearing off a connector or dragging the test setup onto the fl oor is never good. Keep a tidy work space (one I should


also stick to; see Figures 1 and 2) within the limits imposed by getting anything done, at all.


Test signals Any test connection – even an innocent oscilloscope probe – is a potential source of disaster. A tip can short circuit close- spaced pins together. T e earth lead, falling free of its intended test point, can skitter across a board, causing multiple transient short circuits – especially damaging if you’ve leſt the power supply current limit set to a couple of amps. Anticipate useful test nodes in your


circuit, and provide accessible test pads or vias, especially if sections of the circuit are


10 July/August 2026 www.electronicsworld.co.uk


mounted under-soldered on shield cans. Allow for one – or even better, several


– ground tags or pins for the test probe earth clips. On early prototype versions, include


jumpers or extra coupling parts to allow the signal path to be broken. If you are making numerous


connections to a test board, seriously consider building a dedicated test jig, with spring probes.


The RF ports It’s also worth looking specifi cally at RF connection ports, or as they more usually manifest: the 50Ω coax connections to and from the test equipment. Fit the connectors properly. Fully


engage BNC connectors. Use the right torque for SMA and SMC parts. Some smaller connectors (MMCX, UFL


and the like) are fragile. Be aware that higher power RF sources


(transmitters) can produce enough energy to damage test instruments. Treat anything much over 10mW as a


potential enemy – while anything over a watt can actually sting. If uncertain, start with an RF attenuator


in the signal path. Remember that some 50Ω RF ports are


an actual resistive 50Ω to ground, and can be thermally damaged by DC. A 5V DC bias will dissipate half a watt in the port load, which is more than many small attenuators can handle.


The confessional It is all very well preaching from my RF pulpit, but it is in the light of experience – or rather a horrifying parade of errors and


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44