SWL-40+ Building Page of Chuck Adams, K7QO

This page updated November 30, 2016.

On the qrp-tech group at yahoogroups.com, one of the members created a Gerber file for the PCB of the Small Wonder Labs SWL series of transceivers. The kit was retired by Dave Benson, K1SWL, the owner of the company and the architect of the SWL-XX+ series of transceivers.

This page is devoted to the building and testing of the board. I recently gave away my 40m version. So, this is my chance to rebuild one from scratch. I had 10 boards made up from the gerber file and will build the 40m version to test the boards before giving you a chance at doing the same thing. There is a serious obsolete part problem. The transceiver uses 3 42IF123 IF transformers that are no longer available or being manufactured. Mouser has discontinued them along with a large number of Chinese sources and ebay. So, don't consider this project for the future if you do not already have the IF transformers. I recommend you go with the NE4040 or NE3040 transceiver that was Dave's pre-design before the SWL series.

So. I will do the usual build and test by sections and just show the parts installed and a photo. The rest is left to your imagination. Enjoy. Links are to the unmodified and unaltered photos from a Olympus digital camera.

The steps in this build should follow this document. I reserve the right to stray from time to time, if I feel creative or want to test something differently.

  • Small Wonder Labs SW-40+ Construction Manual. May 2011.

  • New PCB. Looking at board from the top.
  • New PCB. Looking at board from the bottom.

    o  install standoffs at the four mounting corners of the PCB
    o  power connector at J1
    o  D13  - 1N4001 or 1N5817 diode for reverse battery protection
    o  C112 - 200uF 25V electrolytic capacitor

  • Installed parts. Stage 1 installation of parts.

    At this point, hook up xcvr to 12V-13.8V power supply. Measure voltages at top of D13. It should be slightly less than the input voltage of the power source. Due to slight voltage drop across the diode and it is not conducting but a very small amount due to the load of the DMM that you are using.

    o   U2  - install 78L08 voltage regulator

  • Installed U2. Stage 2 installation.

    Power up xcvr and measure DC voltage at J2-1, the pad on the left in J2 and next to U2. I get 7.96V on one DMM and 7.86V on a cheap $15 DMM. So your mileage may vary. You just want to make sure you don't have the wrong voltage regulator that will cause damage to ICs.

    The next section gets us some audio to play with.

    o  C102 - 10nF (103), a.k.a. 0.01uF mono or disc cap
    o  D2  - 1N4148 Si diode
    o  R6  - 10 ohm resistor
    o  C106 - 47uF electrolytic cap
    o  C113 - 100nF cap (near D1 and J4)
    o  C107 - 100nF cap
    o  R12  - 1M resistor
    o  R11  - 510K resistor (I substitued a 520K, since I didn't have a 510K)
    o  C26  - 2.2nF (0.0022uF) cap
    o  C25  - 820pF cap
    o  R13  - 1M resistor
    o  C27  - 47uF 25V electrolytic
    o  R14  - 10 ohm resistor
    o  U4   - 8-pin IC socket
    o  U4   - NE5532 IC installed into socket

  • Installed Audio Section for Testing. Stage 3 installation.
  • Installed Audio Section for Testing. Stage 3 installation.

    Once again, power up xcvr. I use powered PC speakers, but headphones will do. Now touch the top of R11. You should hear a increase in the noise level. If you are surrouned by lots of things powered on the AC lines, then it will be loud.

    Now the keying circuit.

    o  Q3  - 2N3906 PNP transistor
    o  R21 - 10K resistor
    o  R20 - 22K resistor
    o  C111 - 10nF cap
    o  C110 - 3.3uF electrolytic cap
    o  R19 - 1K resistor
    o  D11 - 1N5236B (7.5V) zener diode
    o  C109 - 10nF cap

    Power up xcvr and measure voltage at pin 8 of U5 (U5-8). It should read nearly 0.0V. Now take a clip lead (wire with two alligator clips at each end) and connect R21 (the lead furtherest from the board edge) to ground. Now measure the voltage again at U5-8. Should somewhere between 7.5V to 8.0V. This isn't rocket science, so don't worry about the exact value.

  • Installed Keying Section for Testing. Stage 4 installation.
  • Installed Keying Section for Testing. Stage 4 installation.
  • Installed Keying Section for Testing. Stage 4 installation.

    Now the muting circuit.

    o  D5 - 1N4148 diode
    o  R8 - 1M resistor
    o  R10 - 22K resistor
    o  R9 - 4.7M resistor
    o  Q1 - 2N5485 JFET
    o  C24 - 100nF cap

    In my build doc for the SWL40+, previously I got a squeal when powered up at this point. Do not put on headphones and turn the volume down on powered speakers. This can be loud.

    But, for some reason, this build did not result in a squeal. I used 520K instead of 510K and I used 200pF instead of 150pF, since the mono caps supply that I have from the Chinese ebay vendors did not have the 150pF mono. Maybe the difference. Don't know and don't care. :-) It works.

    Now the audio preamp circuit.

    o  D4 - 1N4148 diode
    o  D3 - 1N4148 diode
    o  R7 - 510K resistor
    o  C23 - 150pF cap
    o  R4 - 510K resistor
    o  R2 - 10K resistor
    o  R3 - 10K resistor
    o  C20 - 100nF cap
    o  C19 - 33nF cap
    o  C21 - 10uF electrolytic
    o  C22 - 150pF cap

    Now power up. Touching pins 4 or 5 of U3 gives noise. Maybe loud depending upon your environment.

  • Current board state. Stage 5 installation.

    Now for the receiver mixer section. I have a thousand 4.096MHz crystals that I need to use up, so here goes 5 of them. Dave Benson, K1SWL, used 4.000MHz in the kit, but just about anything in the neighborhood will work. It just means that I have to add a winding or two to the VFO oscillator to get it oscillating at a lower freq to make the sum come out right for VFO + 4.096MHz.

    I did match up the crystals and here is how I did it. See the SWL 40 build manual for details.

  • Crystal matching and testing setup.

    o  U3 socket
    o  C17 - 47pF
    o  C105 - 10nF
    o  C15 - 150pF
    o  R1 - 470 ohms
    o  C105 - 10nF
    o  Y4 - 4.096MHz
    o  C16 - 68pF
    o  U3 - NE602A IC into socket

  • Installed Receiver Mixer Section for Testing.

    Now build the IF crystal filter and front end band pass filter (BPF).

    o  Y3 - 4.096MHz crystal
    o  C14 - 150pF cap
    o  Y2 - 4.096MHz crystal
    o  C13 - 150pF cap
    o  Y1 - 4.096MHz crystal
    o  RFC1 - 22uH molded inductor
    o  C12 - 150pF cap
    o  C11 - 47pF cap
    o  U1 - socket
    o  C3 - 10pF cap
    o  C2 - 47pF cap
    o  C101 - 100nF cap
    o  T1 - 42IF123  (this is the hard part to find now)
    o  C1 - 68pF
    o  U1 - NE602A or NE612A mixer IC

    I powered up the transceiver just to check it out. Touching C1 with a wire increases noise level in the audio. That's about all you can do at this time without the VFO operating.

  • IF crystal filter and Mixer Section and BPF.

    Now build the VFO section.

    o  C103 - 10nF cap
    o  R18 - 1M resistor
    o  D1 - MV1662 varactor diode
    o  R16 - 22K
    o  R15 - 47K resistor
    o  Q2 - 2N4401 NPN transistor
    o  C8 - 82pF cap
    o  C5 - 2700pF (2.7nF) cap
    o  C4 - 2700pF cap
    o  C6 - 3300pF (3.3nF) cap
    o  R17 - 2.2K resistor
    o  C9 - 10pF cap
    o  C10 - 270pF cap
    o  L1 - FT50-6 toroid 25T #26 magnet wire

  • VFO Section.

    Power up transceiver. See if you have a signal at U5-2 or I used a frequency counter to probe the VFO for a freq reading. Experiment, but be careful. The sound, when you touch the pads at C1, is a much narrower bandwidth than previous experiments. IF filter at work.

    o  C109 - 10nF cap
    o  C29 - 150pF cap
    o  C28 - 47pF cap
    o  U5 socket
    o  Y5 crystal
    o  RFC2 - 22uH molded inductor
    o  U5 - NE602A integrated circuit

    Now power up transceiver. Short the lower end of R21 to ground using a small length of INSULATED wire with about 1mm of each end exposed for contact. You should hear a tone in the speakers or headphones.

    o  C30 - 47pF cap
    o  C32 - 47pF cap
    o  C31 - 220pF cap
    o  T1 - 42IF123 IF transformer
    o  T2 - 42IF123 IF transformer
    o  C33 - 10nF cap

    I powered up the transceiver and adjusted T1 and T2 for maximum tone volume in the speakers. This is just a coarse adjustment for now. Fine tuning will occur later.

    o  Q4 - 2N4401 transistor
    o  R23 - 22K resistor
    o  R22 - 10K
    o  R24 - 500ohm variable resistor
    o  C34 - 10nF cap

    Check my assembly manual for step to check the last assembly step. I powered up the transceiver and using a scope checked to see if the output from the variable resistor R24 worked properly.

    OK, now for a lot of stuff in one step....

    o  C114 - 100nF
    o  R28 - 51 ohm resistor
    o  R27 - 10 ohm resistor
    o  Q5 - 2N4401 transistor
    o  R25 - 2.2K
    o  R26 - 470 ohm resistor
    o  T4 - 8:1 T37-43 toroidal transformer
    o  C35 - 10nF cap
    o  RFC3 - 10uH molded inductor
    o  D7 - 1N4148
    o  D8 - 1N4148
    o  D9 - 1N4148
    o  D10 - 1N4148
    o  C40 - 47pF cap
    o  L2 - FT37-43 6T toroid
    o  C36 - 100nF cap
    o  R29 - 51 ohm resistor
    o  D6 - 1N4148 diode
    o  D12 - 1N5256 zener diode
    o  L3 - T37-2 16T toroid
    o  C37 - 470pF cap
    o  C38 - 1nF cap
    o  L4 - T37-2 16T toroid
    o  C39 - 470pF

    My email address is the usual hiding from Internet bots.

    chuck dot adams dot k7qo at gmail dot com