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Toroids. An Introduction By Nicolas - M1HOG. What is Toroid?. Doughnut shaped object whose surface is a torus. Its annular shape is generated by revolving a circle around an axis external to the circle. What is a Toroidal Inductor?.

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An Introduction

By Nicolas - M1HOG

what is toroid
What is Toroid?
  • Doughnut shaped object whose surface is a torus. Its annular shape is generated by revolving a circle around an axis external to the circle.
what is a toroidal inductor
What is a Toroidal Inductor?
  • A coil of insulated wire, usually wound round a core of iron or similar metal in a doughtnut shape.
why use toroids
Why use Toroids?
  • High performance
  • They can be mounted closely together
  • Can be made in a wide range of values and characteristics
  • Simple to make
  • Q – High Quality factor (or Q)
  • Economic!
example uses
Example Uses
  • RF Chokes - An inductor designed to have a high impedance to RF current and low impedance to DC current.
  • Transformer / impedance matching
  • Variable-frequency oscillator (VFO) - The frequency is set by a tuned circuit using capacitors and inductors. The frequency can be changed by adjusting the components in the tuned circuit.
  • Band pass filter - Small capacitor used to tune
  • Mixers - Used intransformers for Diode Ring Mixers.Ready built and homebrew.
  • Many Others
toroids in circuits
Toroids In Circuits

L3 Single winding

toroids in circuits10
Toroids In Circuits

T3 Bifilar winding

construction before we start
Construction - Before we start
  • Counting turns, each pass through the core counts as one turn
  • Coverage 85%
  • Neatness is not generally critical. But get a tidy result and it makes any subsequent checking easier!
  • Wind in the same direction (sometimes direction matters) if only to get the coloured sides all facing the same way!
  • US vs UK wire sizes – Conversion tables
  • Ideally use wire with a heat strippable insulator
construction tools
Construction – Tools
  • Standard workshop tools
  • Pliers - fine
  • Soldering iron
  • Cutters
  • Vice / blu-tack etc to hold toroid while tinning leads etc
  • Magnifier - Ideally illuminated
  • Storage - If you are working on a few toroids; to avoid having to recount turns – was that one 32 or 38 and which core was it wound
construction winding
Construction - Winding
  • Remember every pass through the core counts as a turn
  • Over wind by 3 turns and remove these when complete
  • Pull each turn against the core to ensure it is tight.
  • Thread using a Blunt Darning needle. Not tried this technique myself but some recommend it
  • Don’t rush
construction bifilar winding
Construction – Bifilar Winding
  • Twisting the wire
  • 6 to 8 turns per inch
  • Different colour wires can be used
construction preparing the leads
Construction – Preparing the leads
  • Ideally use wire with a heat strippable insulator
  • Can be stripped with sand paper or a craft knife
  • Strip them back close to the toroid
construction testing and measuring
Construction - Testing and Measuring
  • The Atlas LCR automatically identifies and analyses almost any passive component (Inductor, Capacitor or Resistor). Inductance from 1uH to 10H, Capacitance from 1pF to 10,000uF and Resistance from 1ohm to 2Mohm. Atlas Component Analyser
construction installation
Construction - Installation
  • Pliers to pull the leads through the PCB holes tightly, solder then reheat the joint pulling the wire through to get it tight.
  • Triple check the wiring before cutting of surplus leads. Can be difficult to reinstall with trimmed leads!
construction don t rush
Construction – Don’t Rush
  • Take a break, it does not have to be a marathon!
  • The 30 toroids for this band pass filter board were completed over several lunchtimes, and bottles of beer.
  • G-QRP -
  • Jab -
  • Sycom -
  • Toroid Kits - rate exchange rate!)





G-QRP Club



Goose Island IPA

And Many Others!

thank you
Thank you !

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