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Build this SMT Direct Conversion Module
UNDER CONSTRUCTION - prototype build
Production Version Available ~ Nov 23, 2020

This kit consisting of a Beat Frequency Oscillator and Audio Amplifier that can be used
as a Direct Conversion Receiver of as a Post IF 2nd Mixer Module with Audio Amplifier.
Circuit includes AGC, Mute and Sidetone Input.

Functions & Specs:
xx uV RF input range
500 mWatts Audio Output


This kit does NOT include:
   _____ Power Connector and Power Switch
   _____ PCB Enclosure
   _____ Hookup Wire

For Solder Pencil Soldering, this kit recommends:
   _____ Good Quality 45 Degree Diagonal Tweezers.
   _____ HAKKO FX-888D Temperature Controlled Solder Pencil.
   _____ CircuitWorks CW 3220 Liquid Flux.
   _____ Kester Solder 63/37 .028 - use for other parts.

For Hot Air Soldering, this kit recommends:
   _____ Hot Air Gun Model 858D (or better).
            Search http://ebay.com for item # 274463047101
   _____ CircuitWorks CW 3220 Liquid Flux.
            Search http://ebay.com for item # 202373307435
   _____ Kester Solder 63/37 .020 (0,5 mm) - use for SMDs.
   _____ Mechanic Solder Paste XGZ40 63/37 Paste/Flux 183 Deg C, IPX3, 35g
            Search http://ebay.com for item # 223803694552


Prototype#1 Schematic:


Prototype#1 PCB:



Building Instructions:

1. DO NOT remove any parts from the kit until instructed to do so.

2. Some helpful SMT Info / Links

Surface-Mount Soldering Notes by W8BH, Bruce Hall

Youtube Link About Desoldering And Flux

Youtube Link About Capacitors

Youtube Link General SMT Tutorial

Youtube Link Hot Air SMT



3. Try to limit the handling of the SMT parts; they have a tendancy to disappear.
    If using a hot air gun, you may wish to organize the parts installation into sections.

4. Install these first.
   _____ D4 - 1N5819 labeled as S4 - qty 1 - SMD Part (use this part first for testing)
   _____ U1 - NE612AD Mixer - qty 1
   _____ U2 - LM386-M1 Audio Amp - qty 1

5. Install the unmarked capacitors & varactor diode D1 next.
   _____ Cut the 8.5x11 piece of paper that is holding the unmarked parts into parts strips.
            Only install C10 if using a DDS
   _____ C9,10,14,17 - 33n - qty 4 - install and solder.
   _____ C2,3,13,15,16,20,22,26 - 100n 20% - qty 8 - install and solder.

            C4 value is determined by U1 input frequency.
            0 pF if greater than 9 MHz
            100 pF for 7 MHz if T1 = T37-2[4:30]
            180 pF for 3.5 MHz if T1 = T37-1[4:31]
            120 pF for 1.8 MHz if T1 = T37-61[4:31]
   _____ C4 - 100pF - qty 1 - frequency specific part for 3.561 KHz prototype option

            Do not install C5,7 if using a DDS, else install both.
   _____ C5,7 - 150p - qty 2 - install and solder.
            C5 & C7 values depend of the oscillator frequency; 120 or 150 pF is a tradeoff
            use 220pF for freq below 7 MHz and 100pF for freq above 10 MHz

            C8 value ....
   _____ C8 - ???pF - qty 1 - install and solder.

            C11 value ....
   _____ C11 - ???pF - qty 1 - install and solder.

   _____ C18 - 120p - qty 1 - install and solder.
   _____ C19,24 - 2u2 - qty 2 - install and solder.
   _____ C1,21 - 10uF - qty 2 - install and solder.
            Do not install D1 if using a DDS
            Note the Cathode Line marking for diode D1
            If you can't see the cathode line, compare with a 1N4148 using ohm-meter
   _____ D1 varactor - qty 1 - install and solder. (in small parts bag)

6. Install all SMD 1206 resistors.
            Do not install R1.
            Do not install R2 if using a DDS
   _____ R2,5,11 - 4K7Ω - qty 3 - labeled as 472

            Only install R3 if using a DDS.
   _____ R3 - ???Ω - qty 0 - labeled as ??? install and solder.
            R3 should be scaled so the DDS signal at pin-6 of U1 is 700mV P-P

   _____ R4 - 2KΩ - qty 1 - labeled as 202
   _____ R6,8 - 2M55Ω - qty 1 - labeled as 2554
   _____ R7 - 1MΩ - qty 1 - labeled as 1004
   _____ R9 - 100KΩ - qty 1 - labeled as 104
   _____ R10 - 4R7Ω - qty 1 - labeled as 4R7

7. Install all SMD diodes.
            Note the Cathode Line marking for diode D2
   _____ D2 - 1N4148 - qty 1 - labeled as T4
   _____ D3 - BAT54S (dual diode) - qty 1 - labeled as L44

8. Install the voltage regulator and remaining SMD transistors.
   _____ U3 L78L08 1 labeled as ??
   _____ Q1 2N3904 1 labeled as 1AM
   _____ Q2,3 J113 2 labeled as 6S

9. Install all remaining SMD parts.
   _____ C23 33uF 1 labeled as 336
   _____ C25 220uF 1 labeled as 227
9. Install Trimmer Caps.
   _____ C6 50pF 1 brown trimmer caps (only install with tuned input config)
   _____ C12 50pF 1 brown trimmer caps (only install with VCXO config)

10. Install L1 toroid
            If using a DDS, L1 is part of a PI filter - your design
            If not DDS, L1 inductance sets the range of X1 frequency
   _____ L1 - T37-2 25 turns or more when X1 is greater than 6 MHz
   _____ L1 - FT37-61 12 turns or more when X1 is less than 6 MHz

11. Install Transformer T1 (Balun or Toroid)

   _____ T1 Ferrite Balun BN-43-2402 - for use with CRYSTAL FILTER front end
            Cut 10" of #34 red wire and 4" of #30 red wire.
            Wind 8 turns of #34 red wire on an BN-43-2402 black ferrite binocular.
T5-1.jpg

T5-2.jpg

T5-3.jpg

T5-4.jpg

T5-5.jpg
            Trim the red wires of T1 to one inch each.
            Wind 2 turns of #30 red wire on the BN-43-2402 black ferrite binocular.
            Trim the #30 wires of T1 to one half inch each.
            Strip & Tin the insulation on all 4 wires to the base of the binocular.
            The #34 wire leads for the 8 Turn winding go to the two pads toward the bottom of the PCB connect to C4
            The #30 wire leads go to the two pads in the middle which connect to GND and J1
            Install T1 into the PCB, pull the leads tight using needle nose pliers, solder and trim.

   _____ T1 Powdered Iron Toroid or Ferrite Toroid for TUNED front end

            Remove a FT37-61, T37-2 or T37-6 toroid from the Bag
            Create a transformer with a 1:7 or 1:8 turns ratio (your design)
            Install T1 onto the PCB
T5.jpg

12.   Install the 3-Pin headers onto the PCB

13.   Install all external controls to the PCB

Production Parts List:
Parts List:

Part-ID             Value       Quantity
C1,21               10uF        2 not labeled
C2,3,13,15,16,20,22,26 100n     8 not labeled
C4                  100p frequency specific part, see text
C5,7                150p        2 not labeled
C6,12               50pF        2 brown trimmers
C8                  Oscillator Function Specific, see text
C9,10,14,17         33n         4 not labeled
C11                 Oscillator Function Specific, see text
C18                 120p        1 not labeled
C19,24              2u2         2 not labeled
C23                 33uF        1 labeled as 336
C25                 220uF       1 labeled as 227

R1                  21K         1 labeled as 2102
R2,5,11             4K7         3 labeled as 472
R3                  DDS Function Specific, see text
R4                  2K          1 labeled as 202
R6,8                2M55        2 labeled as 2554
R7                  1M          1 labeled as 1004
R9                  100K        1 labeled as 104
R10                 4R7         1 labeled as 4R7

D1                  1SV324      1 Varactor not labeled (in small parts bag)
D2                  1N4148      1 labeled as T4
D3                  BAT54S      1 (dual diode) labeled as L44
D4                  1N5817      1 1N5819 labeled as S4


Q1                  2N3904      1 labeled as 1AM
Q2,3                J113        2 labeled as 6S

U1                  NE612AD     1 labeled as N612A
U2                  LM386       1 labeled as LM386-M-1
U3                  L78L08      1 labeled as ??

J2 Panel Mount 100KΩ Tune Control
J7 Panel Mount 100KΩ Main Volume Control
J1 input BNC Connector
J8 Output 3.5 mm Speaker Stereo Connector
Nine (9) 3-Pin male headers
SW1 Panel Mount SPTT On/Off/On
Three (3) 3-Pin female housings
Ten (10) female sockets for the above housings
Two (2) 3-Pin female-to-femaile connection cables (suit your needs, cut into four pieces?)

Toroids, Ferrites