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Softrock Lite II Softrock Lite II: Band Pass Filter
Band: 20m

Introduction

General Info About the Stage

Remember, when winding toroidal inductors, a single pass through the core counts as 1 turn. You might want to review Leonard KC0WOX's excellent 10-minute video on winding toroidal coils and transformers.

Also, please refer to the common component mounting instructions for toroids

Theory of Operation

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Stage Schematic

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Board Layouts

Board Top

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Board Bottom

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Band Pass Filter Bill of Materials
( 20m band option)

(details for installation of each component are provided in the step instructions, further down the page)

Be sure to use the correct wire gauge when winding inductor(s)

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Detailed Build Steps

Install Band-specific Capacitors

Install the band-specific capacitors, C3 and C4.

See band-specific chart for values

See hints on identifying and installing Ceramic Capacitors.

Check	Designation	Component (top/bottom)	Orientation	Marking	Image	Band	Notes
☐	C03	47 pF 5% (top)		47J		20m
☐	C04	680 pF 5% (top)		681		20m

Wind and Install Band-specific L1

Inductor Information

Common Techniques:

• Wire Gauge: remember the higher the number, the thinner the wire. E.g., #30 wire is thinner than #26 wire.
• One turn:
  • For toroids, one turn is a single pass through the center hole.
  • For binocular cores, one turn is a pass in which the wire goes in the bottom, comes out the top, goes back in the other hole at the top, and comes out the other hole at the bottom.
• Bi (tri) filar means 2(3) equal lengths of wire. You get the bi(tri)filar strand by taking the length of wire specified for the primary winding, folding it into half(thirds), twisting it to 3~ twists per inch, and winding it over the primary winding. One end of such a strand will have two(three) leads; the other end will have a "hairpin" bend (and a single lead in the case of tri-filar).
• Multi-filar windings are usually done AFTER the uni-filar winding is done.
• Windings shoud be evenly spaced and ideally made such that the winding covers ~345 degrees of the toroid
• Inductance values given are for the single (uni-filar) winding. They are provided to help verify turn counts and core material selected. It's often reported inductances are higher using the theoretical number of turns as calculated by the manufacturer's windings calculator tool, e.g. http://toroids.info/. Normally though these are not too critical, especially with the LF bands antenna noise will still be seen.
• Toroid nomenclature provides the outside diameter of the toroid (in hundredths of an inch - the "30" in "T30-2"), and material code (the "2" in "T30-2"). Color codes used in these kits are:
  • 2=Red
  • 3=Gray
  • 6=Yellow
  • 7=White
  • 10=Black
  • 12=Green (with White on opposite side)

Inductors In This Step

L1

COIL: 2.5uH 26T #30 on T30-6 (yellow)
Using approximately 16 inches of #30 wire, wind 26 turns on a 0.30 inch od T30-6 (yellow) ferrite. Inductance = 2.50 uH.

Install the band-specific coil, L1.

Also, please refer to the common component mounting instructions for toroids

• Do you Run Out of Toroid Before You Run Out of Turns?

  Occasionally, you may find that there is not enough room on the toroid toplace all of the windings without having to go back and add a layer of winding. Tony Parks suggests that you overlap some turns as you put on windings around the circumference of the core so that all turns are on the core by the time you get back to the start end of the winding. This should have negligible effect on the coil's performance in the radio.

• Coil Orientation

  L1 is mounted vertically and supported by its leads.

• Lead Preparation

  Be sure to remove the enamel coating on the wire before attempting to solder an inductor lead to its associated mounting hole. There are two different approaches to removing the enamel and tinning the leads:
  • The enamel coating on the #30 wire provided in the kit does not heat strip very well but may be stripped by use of a small folded over piece of Emory paper where the lead is pulled through two facing surfaces of the Emory paper multiple times to sand off the enamel coating on the wire end. Then you can run each lead through a blob of solder on the hot iron tip to tin it.
  • If you have some solder flux (I use the paste kind), you can slather each lead with flux paste and then run each lead through a hot blob of solder to clean and tin the tip. You may have to repeat the process a couple of times to get all the gunk off of the lead. It produces a well-tinned lead with non of the trauma inherent in stripping the enamel with sandpaper or exacto knife.

Check	Designation	Component (top/bottom)	Orientation	Marking	Image	Band	Notes
☐	L1	2.5uH 26T #30 on T30-6 (yellow) (top)		yellow		20m
☐	L1-core	T30-6 toroid core (top)		yellow		20m

Wind and Install band-specific T1

Inductor Information

Common Techniques:

• Wire Gauge: remember the higher the number, the thinner the wire. E.g., #30 wire is thinner than #26 wire.
• One turn:
  • For toroids, one turn is a single pass through the center hole.
  • For binocular cores, one turn is a pass in which the wire goes in the bottom, comes out the top, goes back in the other hole at the top, and comes out the other hole at the bottom.
• Bi (tri) filar means 2(3) equal lengths of wire. You get the bi(tri)filar strand by taking the length of wire specified for the primary winding, folding it into half(thirds), twisting it to 3~ twists per inch, and winding it over the primary winding. One end of such a strand will have two(three) leads; the other end will have a "hairpin" bend (and a single lead in the case of tri-filar).
• Multi-filar windings are usually done AFTER the uni-filar winding is done.
• Windings shoud be evenly spaced and ideally made such that the winding covers ~345 degrees of the toroid
• Inductance values given are for the single (uni-filar) winding. They are provided to help verify turn counts and core material selected. It's often reported inductances are higher using the theoretical number of turns as calculated by the manufacturer's windings calculator tool, e.g. http://toroids.info/. Normally though these are not too critical, especially with the LF bands antenna noise will still be seen.
• Toroid nomenclature provides the outside diameter of the toroid (in hundredths of an inch - the "30" in "T30-2"), and material code (the "2" in "T30-2"). Color codes used in these kits are:
  • 2=Red
  • 3=Gray
  • 6=Yellow
  • 7=White
  • 10=Black
  • 12=Green (with White on opposite side)

Inductors In This Step

T1

XFRMR: 0.18uH 8T/4T bifilar #30 on T30-6 (yellow)
Primary: Using approximately 7 inches of #30 wire, wind 8 turns on a 0.30 inch od T30-6 (yellow) ferrite.
Secondary: Using a total of 7 inches of #30 wire, wind 4 turns , bifilar, on the ferrite in the same direction as the primary winding. Inductance of the single winding (usually the primary) is 0.18 uH.

If the transformer T1 is not wired correctly to the six holes on the Lite circuit board it can result in very low receiver sensitivity. You should carefully read this section and study the photo below showing how to mount the transformer.

Also, please refer to the common component mounting instructions for toroids and detailed instructions for T1 in the 20m SR Lite II kit. These resources should help the first-time transformer/coil builder past any concerns in that area.

• Primary Winding

• The primary winding is of the band-specific number of turns. Wind the primary winding with the specified number of turns of #30 AWG enameled wire so that the primary winding starts and ends at about the same point on the core and is uniformly spread around the core.

• Secondary Windings

  The secondary uses lengths of #30 wire, twisted together into a bifilar pair that has approximately 2-3 twists per inch and is wound over the primary, using the band-specific number of turns.Wind the secondary windings, in the same direction as the primary, with the windings starting and ending just slightly clockwise around the core from where the primary winding starts and ends.

• ID and Tag the Winding Leads

  After striping and tinning each transformer lead at about 1/8 of an inch from the core, determine the two pairs of leads of each of the secondary windings by use of an ohmmeter. I like to use short lengths of insulation from hookup wire to identify two of the 3 sets of leads in these transformers.

• Transformer Orientation

  (Refer to the graphic, above): Correct wiring is with leads from one side (the "a" side) of the core going to a group of three holes and the leads from the other side (the "b" side) of the core going to the other group of three holes as shown below.
• Note the photo above shows the holes for the primary ("P") and each of the two secondary ("S") leads, with the "a" and "b" designating from which side of the core the particular winding's lead should go.
• for example:
  • The primary winding's "b" lead would go into the left-hand "P" hole
  • The primary winding's "a" lead would go into the right-hand "P" hole
  • The first secondary winding's "b" lead would go into the left-hand "S" hole in the middle row of winding holes
  • The first secondary winding's "a" lead would go into the right-hand "S" hole in the middle row of winding holes
  • and so on …
• Be careful when threading the leads through the holes to avoid their getting tangled up with nearby components!

Check	Designation	Component (top/bottom)	Orientation	Marking	Image	Band	Notes
☐	T1	0.18uH 8T/4T bifilar #30 on T30-6 (yellow) (top)		yellow		20m
☐	T1-core	T30-6 toroid core (top)		yellow		20m

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Completed Photos

Note: the completed pictures are of the 40m option, which the author built. Other band options (which the author did not build) will appear slightly different (especially the inductors, whose windings and cores will vary by band) for the band-specific components.

View of Completed Topside

View of Completed Underside

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Testing

Overview

Test Measurements

Testpoint	Units	Nominal Value	Author's	Yours
Point "P" to point "P"	ohm	0	0	_______
Point "S" to point "S"	ohm	0	0	_______

Test Measurements

Testpoint	Units	Nominal Value	Author's	Yours
R1 hairpin (hole)	Vdc	~2.5	2.47	_______
R2 hairpin (hole)	Vdc	~2.5	2.47	_______

Test Measurements

Testpoint	Units	Nominal Value	Author's	Yours
R1 hairpin (hole)	ohms	~800	803	_______
R2 hairpin (hole)	ohms	~800	803	_______

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Next Stage: Mixer

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