Common Component Monting Tips

Inductors - General Info

Inductors in the Softrock kits are generally wound by the builder on one of two different types of magnetic cores: Toroids or "Binoculars".

Toroidal Cores

A Toroidal core is doughnut-shaped and its color (usually either red or yellow) identifies the type of material. Toroids are typically used for coils and transformers. The toroid's component identifier is of the form "Tdd-m", where the "dd" refers to the outside diameter of the toroid in hundredths of an inch and the "m" designates the material used. Some of the more common toroids found in these kits are:

Binocular Cores

Binocular cores are so-called because their shape calls mind a pair of binoculars. Binocular cores are typically used for chokes and transformers. These kits use binocular cores of two types:

• BN-43-202
• BN-43-2402
• BN-61-2402

If your kit calls for two different types of BN-*-2402 cores, take great care in keeping them separate and marked. The Softrock kits will always - in such case - provide the cores in separate, marked bags. DO NOT MIX THEM UP!

Preparing Binocular Cores for Winding

It is highly recommended to "debur" the holes on the binocular cores to allow for smooth insertion of the wires and avoid inadvertent shorts caused by rough edges to the holes. This can be done using a drill bit that just fits into the holes and "twirling" it between your fingers. Better still (as suggested by Iain,MW0XEN) use a mounted stone from a Dremel type tool (just held in your fingers - not powered). This leaves a very nice rounded edge to the holes.

Winding Specifications

Winding specifications provide the information on the number of windings, the role (e.g., primary or secondary) for each winding on a transformer, and the length and type of wire for the windings.

Specification Format

Winding specs will generally resemble the following:

5.0 uH 17T bifilar/34T #30 on T30-2 (red) (19").

This can be interpreted as:

• Use a T30-2 toroid (color is red and O.D. is 0.3")
• You will need two 19" lengths of #30 wire.
• 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.
• The transformer will have a single, 34 turn, secondary winding of 19" of #30 wire. Usually the single winiding is wound onto the core first. Winding should be evenly spaced and ideally cover all but a 15 degree "wedge" of the toroid. Sometimes, it may be necessary to wind over the top of existing turns where there is more wire than there is bare core left.
• The transformer will have two primary windings each of 17 turns of #30 wire. The term "bifilar" means to take one of the two lengths of wire, bend it at the half-point so the resultant "hairpin" is composed of the two 9.5" long halves, and then twist the two strands together to make a "bifilar" strand with approximately 3 twists to the inch. The bifilar windings are usually wound AFTER (and over) the single strand winding. You should wait until you have wound it correctly before cutting the "hairpin" end of the bifilar strand.
• The inductance value is provided primarily to help validate the number of turns. It is the inductance of the single-strand winding.

Wires

Sometimes the various wires in the kit may be of different colors. Attach no significance to the color; recognize that when the spec calls for a #nn wire, that the "nn" is the gauge of the wire and the higher the gauge number, the thinner the wire.

See the sections below for further details on winding Toroidal and Binocular inductors.

Toroid Coils

Toroids

Identifying the toroids becomes simple once you figure out the coding. The toroids are designated using the pattern "T-NN-M". The critical pieces are the "NN", representing the outside diameter of the "donut" in hundredths of an inch, and the "M", representing the type of material used to make the core. Tony uses the following toroids in his kits:

• T30-2 (red)
• T37-2 (red)
• T25-2 (red)
• T25-6 (yellow)
• T30-6 (yellow)

Toroids are used in single-winding coils and multi-winding transformers. In either case, the number of turns must be counted. Any pass through the center of the Toroid is counted as a "turn" (see below).

Coils

The winding of a single-winding toroidal inductor is fairly straight-forward. Each pass through the center counts as a turn. The windings should be spaced evenly around the circumfrence of the toroid, ideally leaving about a 15 degree "wedge" between the beginning and ending of the winding. The image below is of a 22 turn coil wound on a toroid.

Occasionally, you may find that there is not enough room on the toroid to place 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.

Alan Wolke, W2AEW has a very helpful 8 minute video on Youtube, showing his clever technique for winding toroidal coils using a "sawed-off" chopstick.

Alan also has another video showing how to wind a trifilar transformer of 10 turns:

Leonard, KC0WOX, also has an excellent (if large - 183 Mb!) video showing the winding of a 26 turn coil on a T-37 core. While the turns andcore size in the video are not used in any of the Softrock kits, the technique is essentially the same. The actual process of winding the core begins at about 8.5 minutes into the video.

Clockwise or Counterclockwise?

While the direction of winding of a toroidal coil really makes no difference so long as all windings on that core are in the same direction, it can make a difference in the physical placement of the finished coil on the circuit board. This picture shows two 10-turn coils, one wound clickwise and one wound counter-clockwise. It also shows a typical circuit Board and its silk-screened coil templates. Notice how the clockwise coil will fit correctly in the holes for L2, but will have an awkward fit to the holes for L1. Similarly, notice how the counterclockwise wound coil works for the L1 slot but only awkwardly for the L2 slot. If you wish to have your coils line up like the designer intended, you need to pay attention to the silkscreen slots and the hole positions, mentally trying to place a clockwise-wound coil vs. a counterclockwise-wound one into the slot. You can use these rules of thumb:

• If the coil template is horizontal and the left-hand hole is at the lower left, wind clockwise
• If the coil template is horizontal and the left-hand hole is at the upper left, wind counter clockwise
• If the coil template is vertical and the top hole is on the left, wind clockwise
• If the coil template is vertical and the top hole is on the right, wind counterclockwise

Toroidal Transformers

Winding toroidal transformers usually involves 2 to 3 windings on the same core. The most common is a transformer with a single winding (primary or secondary) over which two "bifilar" windings are superimposed (two secondaries or primaries). See the Toroid Winding Hints from the Experts for good tips on how to wind a toroidal transformer.

In general the transformer outlines on the circuit boards, 4 hole or 6 hole patterns, correspond to the shape of the core involved. The silkscreen lines between opposing hole pairs correspond to the connections for one winding. All that is needed is to connect the leads from one side of the core, or one hole of the core in the case of the binocular cores, to the holes on one side of the pattern the the leads from the other side of the core, or other hole of a binocular core, to the holes on the other side of the pattern. Secondary and primary leads need to be sorted out properly.

When you have finished winding, stripping, and tinning the toroidal transformer's windings, you will two leads for each winding. Each lead will come out on a different side of the toroid. For example, consider a three-winding transformer with one primary ("P") and two secondary windings ("S1" and "S2"). It will have a total of six leads, three on one side of the toroid and three on the opposite side:

• The two primary leads, "Pa" and "Pb" ("P" stands for primary; "a" is one side of the toroid, "b" is the opposite side)
• The two leads for the 1st secondary winding, "S1a" and "S1b" ("S1" stands for the 1st secondary winding; "a" is one side of the toroid, "b" is the opposite side)
• The two leads for the 2nd secondary winding, "S2a" and "S2b" ("S2" stands for the 2nd secondary winding; "a" is one side of the toroid, "b" is the opposite side)
• 

To mount the transformer you insert the leads into the holes annotated on the board as "P", "S1", and "S2". The holes may also be annotated as to the "row" ("a" row or "b" row) which corresponds to the leads on the "a" side or the "b" side of the toroid.

the builder should start with the single winding, inserting its two leads into the appropriate holes and then do the same with the first of the two bifilar windings, and finally do the same with the second of the two bifilar windings

After inserting the leads, the builder should pull each lead pair through the holesuntil the transformer is snug to the board. Soldering the leads completes the process.

Leonard, KC0WOX, has an excellent (large - 100+ Mb!) video showing the winding and mounting of a bifilar transformer on an earlier Softrock (transceiver) kit. He also has a 2 minute video clarifying how bifilar transformers are mounted on Softrock boards.

Binocular Transformers

Debur the Core Before Winding

Binocular cores

• One is the actual winding of the coil. Bino cores can be wound either:
  • with all leads coming out of the same end or
  • with some leads coming out of one end and some coming out of the other.
• All Tony's kits - so far - have used the winding convention where all windings come out of one end of the binocular core, with one turn counted each time the wire goes in one hole and comes out the other, at the same end (see below).
• 
• The other aspect is the correct polarity. That is a little easier, since Tony has designed the boards such that the polarity is pretty well handled for you.
  • The key is to start each winding in the same hole of the bino core and end each winding in the other hole (on the same end of the core).
  • When you finish winding the typical bino transformer with one single wire winding and one bifilar (i.e., twisted pair of wires) wire winding (yielding two windings), you have three wires coming out of each hole on the same end of the core, corresponding to the leads of the three windings.
  • You should carefully strip the insulation from the leads (up to within an eighth of an inck of the core) and tin the leads. Sandpaper can be used to strip the insulation, or you can use an Exacto kinfe to scrape it off. Note that the insulation on the wire Tony provides is normally the heat-strippable type (which you can strip by repeatedly pulling the wire end through a HOT solder blob on the iron tip)..
  • In most of Tony's kits the core is mounted "standing up" vertically and the windings' lead pairs are inserted into the holes corresponding to the winding.
  • For example, if you wind a transformer with one primary (P) and two secondary windings (S1 and S2), you end up with three leads (Pa, S1a and S2a) coming out of one hole and three leads (Pb, S1b, and S2b) coming out of the other hole.
  • The board layout in the enhanced builders notes will usually have annotations on the six holes (for a common transformer) that indicate the lead pairs for the primary, and each of the 2 secondaries.
  • The builder then needs to match the holes with the appropriate winding leads. This graphic is an example:
  • 
  • T201 (above) has one primary and two secondary windings. When wound, it will have 6 leads in all:
    • two leads (Pa and Pb) and
    • four secondary leads (S1a, S2a, S1b, S2a).
    • 
  • You should use an ohmmeter to identify each winding pair.
  Then slip a 1/8" pice of hookup wire insulation onto the Pa and Pb leads to temporarily provide identification of the primary. Also slip a 1/8" piece of insulation onto the S1a and S1b leads to act as a "spacer for the actual mounting.
  • To mount the core, the builder typically starts with the Primary leads, removing the insulation piece and orienting the core such that (in the above instance):
    • the core hole from which Pa lead exits is aligned with the P hole on the top row of the holes and
    • the core hole from which the Pb lead exits is aligned with the P hole on the bottom row.
  • Then insert those primary leads into their corresponding holes.
  • Then take the first pair of S leads (e.g., S1a and S1b) and similarly align with and insert into the "S1" holes (S1a on the top and S1v on the bottom row of holes in the graphic above).
  • Finally do the same thing with the remaining lead pair (S2a and S2b).
  • Then pull through all of the leads from the bottom of the board to ensure no leads have any loose ends or loops topside and the transformer is nice and snug on the board and the 1/8" spacer
  • Solder all leads and you're ready to test them.
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