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? A coil of insulated wire, usually wound round a core of iron or similar metal in a doughtnut shape.

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 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 in transformers for Diode Ring Mixers. Ready built and homebrew. Many Others

Toroid Specification

Toroid T37-2 Physical Dimensions OD = in. / 9.53 mm ID = in. / 5.21 mm Ht = in. / 3.25 mm Magnetic Dimensions = 2.31 cm A = cm 2 V = cm 3 Dimensional Tolerance OD - +/ in. ID - +/ in. Ht - +/ in. A L uH = (A L * Turns 2 ) / Basic Iron PowderCarbonyl SF Material Permeability (µ°)8.5 Temperature Stability (ppm /°C) * averaged from -55C° to +125C 35 Magnetic Tolerance * tested with evenly-spaced windings +/- 5 % Toroidal Color CodeYellow/Clear Resonant Circuit Frequency Range * range is given to optimize Q and core loss 3MHz - 40MHz # of Turns Inductance in uH length in inches includes 1 inch tails " " " " " " " " " " " " "

Toroid Table material #1 u= MHz material #2 u= MHz material #6 u= MHz material #10 u= MHz material #61 u= MHz material #43 u=850 Size->T37T44T50T68 A L -> TurnsInductance in uH, and length in inches " " " " " " " " " " " " " " "

Toroids In Circuits L3 Single winding

Toroids In Circuits T3 Bifilar winding

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 tablesConversion tables Ideally use wire with a heat strippable insulator

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 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 Dont rush

Construction – Bifilar Winding Twisting the wire 6 to 8 turns per inch Different colour wires can be used

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 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 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 - Stability

Construction – Dont 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.

Suppliers G-QRP - Jab - Sycom - Toroid Kits - (Favorable rate exchange rate!)

Credits SADARS Elecraft GM1SXX GW4ALG G-QRP Club Wikipedia W8DIZ Goose Island IPA And Many Others!

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