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 = 0.375 in. / 9.53 mm

ID = 0.205 in. / 5.21 mm

Ht = 0.128 in. / 3.25 mm

Magnetic Dimensions= 2.31 cm

A = 0.064 cm2

V = 0.147 cm3

Dimensional ToleranceOD - +/- 0.015 in.ID - +/- 0.015 in.Ht - +/- 0.02 in.

AL

uH = (AL * Turns2) / 10003.0

Basic Iron Powder Carbonyl 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 Code Yellow/Clear

Resonant Circuit Frequency Range

* range is given to optimize Q and core loss

3MHz - 40MHz

 

# ofTurns

Inductancein uH

lengthin inches

includes1 inch tails

6 .11 5.0"

8 .20 6.0"

10 .31 7.0"

12 .44 8.0"

14 .60 9.0"

16 .78 10.0"

18 1.0 11.0"

20 1.2 12.0"

22 1.5 13.0"

24 1.8 14.0"

26 2.1 15.0"

28 2.4 16.0"

30 2.7 17.0"

Toroid Tablematerial #1  u=20  0.5-5 MHzmaterial #2  u=10  2-30 MHz

material #6  u=8.5  10-50 MHzmaterial #10  u=6  30-100 MHz

material #61  u=125  0.2-15 MHzmaterial #43  u=850  

Size-> T37 T44 T50 T68

AL-> 40  30  55.3  420 52  42 100  49  40  31  68  523 57  47

Turns Inductance in uH, and length in inches

6 .14  .11  1.99  15.1  5.00" .19  .15 .18  .14  2.45  18.8  5.75" .21  .17  6.50"

8 .26  .19  3.54  26.9  6.00" .33  .27 .31  .26  4.35  33.5  7.00" .37  .30  8.00"

10 .40  .30  5.53  42.0  7.00" .52  .42 .49  .40  6.80  52.3  8.25" .57  .47  9.50"

12 .58  .43  7.96  60.5  8.00" .75  .60 .71  .58  9.79  75.3  9.50" .82  .68  11.00"

14 .78  .59  10.8  82.3  9.00" 1.0  .82 .96  .78  13.3  102  10.75" 1.1  .92  12.50"

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 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

• Don’t 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 – 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.

Suppliers

• G-QRP - http://www.gqrp.com/• Jab - http://www.gqrp.com/• Sycom - http://www.sycomcomp.co.uk/• Toroid Kits - http://qrpkits.com/

(Favorable rate exchange rate!)

Credits

SADARS

Elecraft

GM1SXX

GW4ALG

G-QRP Club

Wikipedia

W8DIZ

Goose Island IPA

And Many Others!

Thank you !

This presentation is available at

www.M1HOG.com