Softrock Lite II 05_Band Pass Filter

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	Marking	Category	Orientation	Notes
❏	C03	band-specific	Band Component Marking 160m 390 pF 5% (Ceramic) 391 80m 220 pF 5% (Ceramic) 221 40m 100 pF 5% (Ceramic) 101 30m 68 pf 5% (Ceramic) 68J 20m 47 pF 5% (Ceramic) 47J	misc
❏	C04	band-specific	Band Component Marking 160m 5600 pF 5% (Ceramic) 562 80m 3300 pF 5% (Ceramic) 332 40m 1500 pF 10% (Ceramic) 152 30m 1000 pF 5% (Ceramic) 102 20m 680 pF 5% (Ceramic) 681	misc

Wind and Install Band-specific L1

Install the band-specific coil, L1.

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

Band-Specific Details

L1, for all bands, uses #30 wire and T30-6 toroid core. Turn counts, wire lengths, and inductance per band are shown in the table below:

• BOM Notation

  Wind the band-specific number of turns of #30 wire onto the band-specific toroidal core. E.G., "9.1 uH 50T #30 on T30-6 (yellow) (26")" means use 26 inches of #30 wire to wind 50 turns onto a T30-6 toroid

• Turn Counting

  Each pass through the center of the core is counted as a turn when winding the inductor.

• 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	Marking	Category	Orientation	Notes
❏	L1	band-specific	Band Component Marking 160m 19.6 uH 74T #30 on T30-6 (yellow) (38") (Coil) yellow 80m 9.1 uH 50T #30 on T30-6 (yellow) (26") (Coil) yellow 40m 5.0 uH 37T #30 on T30-6 (yellow) (20") (Coil) yellow 30m 3.5 uH 31T #30 on T30-6 (yellow) (17") (Coil) yellow 20m 2.5 uH 26T #30 on T30-6 (yellow) (15") (Coil) yellow	misc

Wind and Install band-specific T1

If 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.

• Band-Specific Transformer Details

  The transformer is wound with a primary winding and two secondary windings. The two secondary windings are created by folding the specified length of wire over double ("bifilar") and winding the doubled wire the required number of (secondary) turns. See table below for Core, Length, Turns, and Primary Inductance info. ("Turns 10/5" Means primary is 10 turns and secondaries are 5 turns bifilar):

  Band	Core	Length	Turns(p/s)	µH(p)
  160m	T30-6 (yellow)	13"	20/10	1.4
  80m	T30-6 (yellow)	10"	14/7	0.73
  40m	T30-6 (yellow)	8"	10/5	0.35
  30m	T30-6 (yellow)	7"	8/4	0.18
  20m	T30-6 (yellow)	7"	8/4	0.18

• BOM Notation

  The winding details will be in the form: "nnT/2 x mmT bifilar #30" on Txx-x (LL")". This translates to:
  • Using a toroid Txx-x and LL inches of #30 wire, wind a primary with nn turns
  • then, using the same length of #30 wire folded in half, wind the 2 secondaries on top of the primary for mm turns

• 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, below): 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 below 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	Marking	Category	Orientation	Notes
❏	T1	band-specific	Band Component Marking 160m 1.4 uH 20T/10T bifilar #30 on T30-6 (yellow) (13") (Xfrmr) yellow 80m 0.73 uH 14T/7T bifilar #30 on T30-6 (yellow) (10") (Xfrmr) yellow 40m 0.35 uH 10T/5T bifilar #30 on T30-6 (yellow) (8") (Xfrmr) yellow 30m 0.18 uH 8T/4T bifilar #30 on T30-6 (yellow) (7") (Xfrmr) yellow 20m 0.18 uH 8T/4T bifilar #30 on T30-6 (yellow) (7") (Xfrmr) yellow	misc