Auto Band Pass Filters Introduction

General

This stage implements the automatic bandpass filtering circuit. The circuit uses two quad multiplexer switches to switch one of four bandpass filters into the QSD input. The filters provide continuous coverage, in four "chunks", from 1.8MHa through 30 MHz (with some under and overlaps).

Switching is automatic, via the two binary signals, "FL SEL 0" and "FL SEL 1". The ATTiny 85 Microcontroller has a built-in band plan which associates any output frequency of the Local Oscillator to the most appropriate filter and issues the corresponding bits to "FL SEL 0" and "FL SEL 1", per the following truth table:

Filter Selection Truth Table
Sel 1 (R12)Sel 0 (R13)FilterLF (MHz)HF (MHz)
LL014
LH148
HL2816
HH31630
(SEL-0 is at the hairpin lead of R13; SEL-1 is at the hairpin lead of R12)

These notes detail the construction of each of the four bandpass filters, with a simple continuity test at the end of each filter's construction to verify soldering of the leads of the coils.

If you are unfamiliar with toroid and binocular inductor construction, please see the WB5RVZ Construction hints for inductors.

(Note: completed photos of this and the next stage were, unfortunately not taken at stage-end. The completed photos shown are from the final stage, with the uninstalled sections photoshopped out. Apologies.)

(go directly to build notes)

Auto Band Pass Filters Schematic

(Resistor testpoints (hairpin, top, or left-hand lead), as physically installed on the board, are marked in the schematic with red dots)

(Click for Full Schematic)
Auto Band Pass Filtersschematic

(above schematic has clickable areas that can be used for navigation)

(go directly to build notes)

Auto Band Pass Filters Bill of Materials

Stage Bill of Materials

(resistor images and color codes courtesy of WIlfried, DL5SWB's R-Color Code program)

CheckCountComponentMarkingCategory
210 ohm 1/4W 1%br-blk-blk-gld-br br-blk-blk-gld-br1/4W
2120 1/6W 5%brn-red-brn-gld brn-red-brn-gld1/6W
42.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W
22.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W
475 1/6W 5%vio-grn-blk-gld vio-grn-blk-gld1/6W
2BN-43-2402 (no markings!)none noneBinocular core
20.047 uF 5%473 473Ceramic
2100 pF 5%101 101Ceramic
21500 pF 10%152 152Ceramic
2180 pF 5%181 181Ceramic
3390 pF 5%391 391Ceramic
3680 pF 5%681 681Ceramic
10.13 uH: 7T #30 (5") on T25-6 coreyellow yellowcoil
10.27 uH: 10T #30 (6") on T25-6 coreyellow yellowcoil
30.46 uH: 13T #30 (7") on T25-6 coreyellow yellowcoil
21.0 uH: 19T #30 (9") on T25-6 coreyellow yellowcoil
22.0 uH: 27T #30 (12") on T25-6 coreyellow yellowcoil
12.6 uH: 31T #30 (13") on T25-6 coreyellow yellowcoil
25.5 uH: 45T #30 (18") on T25-6 coreyellow yellowcoil
1BNC Connector Male - PCB mount Jack
1Magnetic Wire, enameled #30Magnetic
1Magnetic Wire, enameled #30Magnetic
1Magnetic Wire, enameled #30Magnetic
1Magnetic Wire, enameled #30Magnetic
60.1 uF(smt) black stripe (smt) black stripeSMT 1206
2FST3253 mux/demux switchFST3253 FST3253SOIC-16
12T25-6 toroid coreyellow yellowToroid
14T bifilar #30 on BN-43-2402 (9") xfrmr
14T/2Tbifilar #30 on BN-43-2402 (7") xfrmr

Auto Band Pass Filters Summary Build Notes

Auto Band Pass Filters Detailed Build Notes

Top of the Board

Auto Band Pass Filters Top View

Install BPF In/Out Components

Includes winding and installing the two transformers (one binocular, one toroidal), T2 and T3.

Once the transformers are wound and installed, you should turn the board over and run continuity tests on the primary and secondary windings, per the above diagram

CheckDesignationComponentMarkingCategoryOrientationNotes
R232.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WW-E
T024T bifilar #30 on BN-43-2402 (9") xfrmr 
T034T/2Tbifilar #30 on BN-43-2402 (7") xfrmr 
R152.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WN-S
R162.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WN-S
R242.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6WW-E
R2510 ohm 1/4W 1%br-blk-blk-gld-br br-blk-blk-gld-br1/4WE-W
R2610 ohm 1/4W 1%br-blk-blk-gld-br br-blk-blk-gld-br1/4WE-W
R272.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W 
R282.2k 1/6W 5%red-red-red-gld red-red-red-gld1/6W 

Install and Continuity Test the 160m BPF

In this step and the two steps following it, you will build the bandpass filter for the 160m passband.

First, you want to wind and install the coils and then continuity test them. The continuity test checks for continuity between the points labeled "1" and then tests the continuity between the points labeled "2". Wherever possible, the test points have been assigned to vias removed from but electrically connected to the coils' vias, so as to give a good test of the soldering.

Once you have successfully verified continuity, you can proceed to install the remaining parts for the passband.

Install and Continuity Test the 160m BPF photo
CheckDesignationComponentMarkingCategoryOrientationNotes
magwire_50inMagnetic Wire, enameled #30Magnetic 
50 inches #30

Install the 160m Inductors

If you are unfamiliar with winding and installing inductors, you may want to refer to the WB5RVZ construction hints for coils (toroidal) and transformers ( toroidal and binocular). Click here for details on identifying toroid cores.

Decoding the trqansformer specifications:

Transformers' windings are specified using the pattern "nnT/wXmmT" or "wXmmT/nnT", where:

  • "nn" is the number of turns in the single winding
  • "mm" is the number of turns in the multiple windings
  • "w" = the number of multiple windings (e.g., 2 = bifilar; 3 = trifilar, etc.)

Thus, e.g., "18T/2x9T bifilar #30" means, using #30 wire, produce a single 18 turn primary winding and two 9-turn secondary windings; "2x9T bifilar/ 18T #30" means, using #30 wire, produce two 9-turn primary windings and a single 18 turn secondary winding.

CheckDesignationComponentMarkingCategoryOrientationNotes
L015.5 uH: 45T #30 (18") on T25-6 coreyellow yellowcoil 
L022.6 uH: 31T #30 (13") on T25-6 coreyellow yellowcoil 
L035.5 uH: 45T #30 (18") on T25-6 coreyellow yellowcoil 

Install the 160m Static Components

CheckDesignationComponentMarkingCategoryOrientationNotes
C060.047 uF 5%473 473Ceramicvert
C07680 pF 5%681 681Ceramicvert
C081500 pF 10%152 152Ceramichoriz
C09680 pF 5%681 681Ceramichoriz
R1775 1/6W 5%vio-grn-blk-gld vio-grn-blk-gld1/6WS-N
R18120 1/6W 5%brn-red-brn-gld brn-red-brn-gld1/6WN-S
R1975 1/6W 5%vio-grn-blk-gld vio-grn-blk-gld1/6WE-W

Install and Continuity Test the 80/40m BPF

In this step and the two steps following it, you will build the bandpass filter for the 80/40m passband.

First, you want to wind and install the coils and then continuity test them. The continuity test checks for continuity between the points labeled "1" and then tests the continuity between the points labeled "2". Wherever possible, the test points have been assigned to vias removed from but electrically connected to the coils' vias, so as to give a good test of the soldering.

Once you have successfully verified continuity, you can proceed to install the remaining parts for the passband.

Install and Continuity Test the 80/40m BPF photo
CheckDesignationComponentMarkingCategoryOrientationNotes
magwire_24inMagnetic Wire, enameled #30Magnetic 
24 inches #30

Install the 80/40m Inductors

If you are unfamiliar with winding and installing inductors, you may want to refer to the WB5RVZ construction hints for coils (toroidal) and transformers ( toroidal and binocular). Click here for details on identifying toroid cores.

Decoding the trqansformer specifications:

Transformers' windings are specified using the pattern "nnT/wXmmT" or "wXmmT/nnT", where:

  • "nn" is the number of turns in the single winding
  • "mm" is the number of turns in the multiple windings
  • "w" = the number of multiple windings (e.g., 2 = bifilar; 3 = trifilar, etc.)

Thus, e.g., "18T/2x9T bifilar #30" means, using #30 wire, produce a single 18 turn primary winding and two 9-turn secondary windings; "2x9T bifilar/ 18T #30" means, using #30 wire, produce two 9-turn primary windings and a single 18 turn secondary winding.

CheckDesignationComponentMarkingCategoryOrientationNotes
L042.0 uH: 27T #30 (12") on T25-6 coreyellow yellowcoil 
L050.46 uH: 13T #30 (7") on T25-6 coreyellow yellowcoil 
L062.0 uH: 27T #30 (12") on T25-6 coreyellow yellowcoil 

Install the 80/40m Static Components

CheckDesignationComponentMarkingCategoryOrientationNotes
C100.047 uF 5%473 473Ceramicvert
C11390 pF 5%391 391Ceramicvert
C121500 pF 10%152 152Ceramichoriz
C13390 pF 5%391 391Ceramichoriz
R2075 1/6W 5%vio-grn-blk-gld vio-grn-blk-gld1/6WS-N
R21120 1/6W 5%brn-red-brn-gld brn-red-brn-gld1/6WN-S
R2275 1/6W 5%vio-grn-blk-gld vio-grn-blk-gld1/6WW-E

Install and Continuity Test the 30/20/17m BPF

In this step and the two steps following it, you will build the bandpass filter for the 30/20/17m passband.

First, you want to wind and install the coils and then continuity test them. The continuity test checks for continuity between the points labeled "1" and then tests the continuity between the points labeled "2". Wherever possible, the test points have been assigned to vias removed from but electrically connected to the coils' vias, so as to give a good test of the soldering.

Once you have successfully verified continuity, you can proceed to install the remaining parts for the passband.

Install and Continuity Test the 30/20/17m BPF photo
CheckDesignationComponentMarkingCategoryOrientationNotes
magwire_24in_aMagnetic Wire, enameled #30Magnetic 
24 inches #24

Install the 30/20/17m Inductors

If you are unfamiliar with winding and installing inductors, you may want to refer to the WB5RVZ construction hints for coils (toroidal) and transformers ( toroidal and binocular). Click here for details on identifying toroid cores.

Decoding the trqansformer specifications:

Transformers' windings are specified using the pattern "nnT/wXmmT" or "wXmmT/nnT", where:

  • "nn" is the number of turns in the single winding
  • "mm" is the number of turns in the multiple windings
  • "w" = the number of multiple windings (e.g., 2 = bifilar; 3 = trifilar, etc.)

Thus, e.g., "18T/2x9T bifilar #30" means, using #30 wire, produce a single 18 turn primary winding and two 9-turn secondary windings; "2x9T bifilar/ 18T #30" means, using #30 wire, produce two 9-turn primary windings and a single 18 turn secondary winding.

CheckDesignationComponentMarkingCategoryOrientationNotes
L071.0 uH: 19T #30 (9") on T25-6 coreyellow yellowcoil 
L080.27 uH: 10T #30 (6") on T25-6 coreyellow yellowcoil 
L091.0 uH: 19T #30 (9") on T25-6 coreyellow yellowcoil 

Install the 30/20/17m Static Components

CheckDesignationComponentMarkingCategoryOrientationNotes
C14180 pF 5%181 181Ceramichoriz
C15680 pF 5%681 681Ceramichoriz
C16180 pF 5%181 181Ceramichoriz

Install and Continuity Test the 15/12/10m BPF

In this step and the two steps following it, you will build the bandpass filter for the 15/12/10m passband.

First, you want to wind and install the coils and then continuity test them. The continuity test checks for continuity between the points labeled "1" and then tests the continuity between the points labeled "2". Wherever possible, the test points have been assigned to vias removed from but electrically connected to the coils' vias, so as to give a good test of the soldering.

Once you have successfully verified continuity, you can proceed to install the remaining parts for the passband.

Install and Continuity Test the 15/12/10m BPF photo
CheckDesignationComponentMarkingCategoryOrientationNotes
magwire_19inMagnetic Wire, enameled #30Magnetic 
19 inches #24

Install the 15/12/10m Inductors

If you are unfamiliar with winding and installing inductors, you may want to refer to the WB5RVZ construction hints for coils (toroidal) and transformers ( toroidal and binocular). Click here for details on identifying toroid cores.

Decoding the trqansformer specifications:

Transformers' windings are specified using the pattern "nnT/wXmmT" or "wXmmT/nnT", where:

  • "nn" is the number of turns in the single winding
  • "mm" is the number of turns in the multiple windings
  • "w" = the number of multiple windings (e.g., 2 = bifilar; 3 = trifilar, etc.)

Thus, e.g., "18T/2x9T bifilar #30" means, using #30 wire, produce a single 18 turn primary winding and two 9-turn secondary windings; "2x9T bifilar/ 18T #30" means, using #30 wire, produce two 9-turn primary windings and a single 18 turn secondary winding.

CheckDesignationComponentMarkingCategoryOrientationNotes
L100.46 uH: 13T #30 (7") on T25-6 coreyellow yellowcoil 
L110.13 uH: 7T #30 (5") on T25-6 coreyellow yellowcoil 
L120.46 uH: 13T #30 (7") on T25-6 coreyellow yellowcoil 

Install the 15/12/10m Static Components

CheckDesignationComponentMarkingCategoryOrientationNotes
C17100 pF 5%101 101Ceramicvert
C18390 pF 5%391 391Ceramichoriz
C19100 pF 5%101 101Ceramichoriz

Install Antenna Jack

CheckDesignationComponentMarkingCategoryOrientationNotes
J04BNC Connector Male - PCB mount Jack 

Bottom of the Board

Auto Band Pass Filters Bottom View

Install Bottomside Components

CheckDesignationComponentMarkingCategoryOrientationNotes
U08FST3253 mux/demux switchFST3253 FST3253SOIC-16 
U09FST3253 mux/demux switchFST3253 FST3253SOIC-16 
C370.1 uF(smt) black stripe (smt) black stripeSMT 1206white pads
C380.1 uF(smt) black stripe (smt) black stripeSMT 1206yellow pads
C390.1 uF(smt) black stripe (smt) black stripeSMT 1206yellow pads
C400.1 uF(smt) black stripe (smt) black stripeSMT 1206yellow pads
C410.1 uF(smt) black stripe (smt) black stripeSMT 1206white pads
C420.1 uF(smt) black stripe (smt) black stripeSMT 1206yellow pads

Auto Band Pass Filters Completed Stage

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

Auto Band Pass Filters Testing

Pin Voltages on the Ics

Test Setup

Run the Filter Selection Test from the LO and Control Stage, only instead of measuring the voltages at the hairpin leads of R12 and R13, measure the voltages at the 2 and 14 PINS (not the pads) of U8 and U9. This will validate that the pins were correctly soldered to the pads and are getting the switching signals.

Perform the tests below for each of U8 and U9

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
LO=2 MHz (band 0) - Test pin 2 (FL SEL 1)V dc0100 mV_______
LO=2 MHz (band 0) - Test pin 14 (FL SEL 0)V dc0100 mV_______
LO=6 MHz (band 1) - Test pin 2 (FL SEL 1)V dc0100 mV_______
LO=6 MHz (band 1) - Test pin 14 (FL SEL 0)V dc54.92_______
LO=12 MHz (band 2) - Test pin 2 (FL SEL 1)V dc54.92_______
LO=12 MHz (band 2) - Test pin 14 (FL SEL 0)V dc0100 mV_______
LO=24 MHz (band 3) - Test pin 2 (FL SEL 1)V dc54.92_______
LO=24 MHz (band 3) - Test pin 14 (FL SEL 0)V dc54.92_______

(Optional) RF Test

Test Setup

If you have a scope and a signal source (or an RF probe and a signal source)

Inject an RF signal of around 50-100 mV at the antenna jack, determine which band should switch for that RF signal, and probe the pins of U8 and U9 which should be switched to that signal:

BandSwitched Pins
0 (1-4 MHz)6 & 10
1 (4-8 MHz)5 & 11
2 (8-16 MHz)4 & 12
3 (16-30 MHz)3 & 13

Your scope should show the signal at the switched pins and not at any of the other pins.

(Optional) RF Test
Filter Selection Signals from Local Oscillator/Control uC Filtered RF in antiphase as input to QSD ("mixer") from power supply from power supply 2.5V test point 2.5 V testpoint