QRPGuys Digital DSB II Transceiver Kit User manual

Page 1 of 16 ft8_II_assy_smd_diode_072020.pdf
QRPGuys Digital DSB II Transceiver Kit, w/smd mixer
First, familiarize yourself with the parts and check for all the components. If a part is missing,
please contact us at [e-mail] and we will send you one.
Please read all the instructions before starting to assemble the transceiver.
Parts List:
Location Quantity value Type
C1, C2, C10, C13, C16 5 10 nF - 103 X7R MMLC
C3, C7 2 100 uF electrolytic ≥16V Long lead plus
C4, C5, C6, C8, C9, C12, C14,
C15, C18, C19, C20, C22
12 100 nF - 104 X7R MMLC
C11, C17, C21 3 1 uF electrolytic ≥16V Long lead plus
D1 1 1N5817 BLACK PLASTIC
D2, D3 2 1N4148 SMALL GLASS
D4 1 CLEAR LENS RED LED
D5 1 1N4756 47V 1W ZENER SMALL GLASS
J1 1 BNC JACK PCB MOUNT
J2 1 2.1mm DC JACK PCB MOUNT
J3, J4 2 3.5mm PHONE JACK STEREO, SWITCHED
J5, J6, J7 3 5 POSITION SIP JACK 0.1” CENTERS
L4 1 10 uH choke BRN/BLK/BLK/GLD or
BRN/BLK/BLK/SIL

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Q1, Q2, Q4, Q6, Q7, Q8 6 BS170 TO-92 MOSFET
Q3, Q9 2 2N3904 TO-92 NPN
Q5 1 2N3906 TO-92 PNP
R11, R20 2 5.6 OHMS GRN/BLUE/GOLD/GLD
R1 1 51 OHMS GRN/BRN/BLK/GLD
R10, R19 2 470 OHMS YEL/VIO/BRN/GLD
R4, R9, R18, R21 4 1K BRN/BLK/RED/GLD
R5 1 4.7K YEL/VIO/RED/GLD
R2, R3, R12, R16, R17 5 10K BRN/BLK/ORG/GLD
R14 1 47K YEL/VIO/ORG/GLD
R6, R8 2 100K BRN/BLK/YEL/GLD
R13 1 470K YEL/VIO/YEL/GLD
R15 1 680K BLUE/GRY/YEL/GLD
R7 1 1 MEG BRN/BLK/GRN/GLD
U1 1 SA602 or SA612A SO8 MIXER/OSC
U2 1 LM358 DIP8 DUAL OPAMP
U3 1 LM7809 TO-220 9V/1A REG
V1, V2 2 2K 6mm Trimmer resistor
T1, T2 2 FT37-43 FERITE CORE, BLACK
DIP SOCKET 1 8 PIN DIP SOCKET
PCB 1 MAIN CIRCUT BOARD
Screw 1 4-40 1/4”
Nut 1 4-40 nut
FEET 4 RUBBER FEET
TEST pins 1 2 position SIP pin strip
1 Jumper (Berg connector)
BAND PARTS, SEE TABLE QUANITIY VALUE
CAPACITORS 6 22 pF – marked 22 or 220 C0G
1 33 pF – marked 33 or 330 C0G
1 47 pF – marked 47 or 470 C0G
1 68 pF – marked 68 or 680 COG
3 100 pF – marked 101 C0G
2 150 pF – marked 151 C0G
2 220 pF – marked 221 C0G
3 330 pF - marked 331 C0G
1 560 pF – marked 561 C0G
1 680 pF – marked 681 C0G

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INDUCTORS 1 0.68 uH BLU/GRY/SIL/GLD or
BLU/GRY/SIL/SIL
1 1.2 uH BRN/RED/GLD/GLD or
BRN/RED/GLD/SIL
1 2.2 uH RED/RED/GLD/GLD or
RED/RED/GLD/SIL
4 T37-2 RED CORES
2 T37-6 YELLOW CORES
crystals 1 7.074 MHz HC-49/US
1 10.136 MHz HC-49/US
1 14.074 MHz HC-49/US
Miscellaneous 3 Band module boards
12'
1’
#26 magnet wire
#26 magnet wire, diff. color
12 Small tie wraps
P1, P2 6 5 position 90° SIP pin strips
Parts placement diagram: Print this page for quick reference

Page 4 of 16 ft8_II_assy_smd_diode_072020.pdf
Assembly:
The first step is to sort the parts into groups of similar types. This will make finding the needed
part type and value quicker.
All components mount on the front side of the pcb.
The first item to install is the only SMD component. We needed to change from the DIP8 form to
the SO8 surface mount form because of shrinking availability and to keep the kit low priced.
Use your favorite smd soldering method or we have found the process below to be quite
satisfactory.
[ ] Solder U1, the SA602/612, smd component first, by wiping a thin layer of flux on the board,
position the chip, carefully noting the flat along the side and top edge for the orientation of Pin 1,
and touch each pin with a dry iron. Once you are sure of the orientation, you can go back and add
a little solder to each pin if needed. Be sure there are no solder bridges between pins. Use Solder
Wick® if necessary to remove any excess. Do a continuity check with an ohm meter from each pin
of U1 to the end of the trace to check your work. Note that pin 3 is GND.

Page 5 of 16 ft8_II_assy_smd_diode_072020.pdf
Resistors:
Caution: Several of the values have very similar color codes and differ only by the zero
multiplier color. It is also easy to mix up the 51 and 1 Meg resistors as 51 is
green/black/brown/gold and 1 meg is brown/black/green/gold.
L4 is a RF choke. It looks like a resistor, but is a bit fatter. With an ohm meter, it will
read 0 ohms.
[ ] R1 - 51 GRN/BRN/BLK/GLD
[ ] R2, 3, 12, 16, 17 – 10K BRN/BLK/ORG/GLD
[ ] R4, R9, R18, R21 - 1K BRN/BLK/RED/GLD
[ ] R5 - 4.7K YEL/VOL/RED/GLD
[ ] R6, R8 - 100K BRN/BLK/YEL/GLD
[ ] R7 - 1 Meg BRN/BLK/GRN/GLD
[ ] R10, R19 - 470 YEL/VOL/BRN/GLD
[ ] R11, R20 - 5.6 GRN/BLU/GLD/GLD
[ ] R13 – 470K YEL/VOL/YEL/GLD
[ ] R14 – 47K YEL/VOL/ORG/GLD
[ ] R15 – 680K BLU/GRY/YEL/GLD
[ ] L4 – 10 uH BRN/BLK/BLK/GLD or
BRN/BLK/BLK/SIL
[ ] D1 – 1N5817 Black plastic body
[ ] D2, D3 – 1N4148 Small Glass body
[ ] D5 – 1N4756A ZENER Larger Glass body
Match the diode stripe on the component with
the silkscreen
Capacitors:
[ ] C1, C2, C10, C13, C16 – 103 Orange
highlight
[ ] C4,5,6,8,9,12,14,15,18,19,20,22 – 104 –
Yellow highlight 12 places
[ ] C11, C17, C21 – 1 uF – long lead is plus.
These caps need to be laid down flat to the
board.
[ ] C3, C7- 100 uF – long lead is plus.
Note: When reading capacitor values, do
not confuse the manufacturing codes with
the component value. If it looks strange it
may be a manufacturing code, look on the
other side of the component. Also, the
value may be followed by a tolerance code
- M,K, or J.

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Everything else:
[ ] U3 – 7809 Bend the leads at the point
where they narrow. Secure with 4-40 screw
and nut.
[ ] J5, J6, J7 – 5 pins SIP socket. Make sure
these are set square to the board before
soldering more than one pin.
[ ] U2 - 8 pin DIP socket. Note orientation of
notch on socket and match with notch on part
board outline. Make sure all the pins are
sticking out the solder pads before soldering
any!
[ ] J3, J4 – 3.5mm phone jacks
[ ] Q1, Q2, Q4 – BS170 MOSFET Note
orientation of the flat side of part. Make sure it
matches the board outline.
[ ] Q3, Q9 – 2N3904 NPN
[ ] Q5 – 2N3906 PNP
[ ] Q6, Q7, Q8 – These parts require some heat sinking. Therefore, these parts get mounted with
the flat side of the package pressed against the large, tinned pad to the left of the board. Make
“U” shaped pieces of resistor lead clippings to hold the body of the BS170's to the board, using
the small holes on either side of the package.
[ ] D4 – CLEAR LENS RED LED – the short lead goes into hole on flat side of part outline.
[ ] TEST – 2 pin SIP header, short pin end in the board
[ ] V1, V2 – 2K trimmer pots
[ ] J2 – DC power Jack.
[ ] J1 – BNC antenna jack
[ ] T1, T2 – bifilar wound on T37-43 ferrite core
(black).
 Cut 6” length of each color magnet wire
 The two wires can be lightly twisted
together, but this is not necessary
 Wind 5 turns on the core as shown.
 Trim and tin the wire ends. Either scrape or
melt the insulation using a hot iron with a
blob of solder.
 Orientate the common wire ends so they are opposite each other on the core.
 The wires will now be in the proper position for inserting into the board.
Be sure to tin the wire ends before installing. This is a leading cause of failure. Be sure
not to pull the wire thru the hole past where you have it tinned.

Page 7 of 16 ft8_II_assy_smd_diode_072020.pdf
Special Note:
Do not proceed until you make this check. If you have installed T1 correctly, you should read
0 ohms with an ohm meter between the two pads marked by the red arrows on T1. If you have
installed T2 correctly, you should read 0 ohms with an ohm meter between the two pads marked
by the blue arrows on T2. If not, investigate and correct before going any further.
[ ] Stick the rubber bumper feet on the bottom of the board.
Assembling the band modules:
We supply three band modules and detailed the values for 20/30/40m. Additional bare band
module pcb’s are available for operation on other bands. At the end of this document we have
modeled additional band component values. They are starting points; tweaking of the values may
be necessary, and you will need to source your own components.
[ ] Before populating with components, mark each module with the band in the space
provided with a permanent marker. They can easily get mixed up during assembly and
difficult to correct.
[ ] J5,J6 – 5 pin right angle SIP header strip. Short 90° pins go into board. Mount on the top of
the board as shown.
Use the placement graphic and tables below to install the capacitors, crystals, and inductors.

Page 8 of 16 ft8_II_assy_smd_diode_072020.pdf
Note: When reading module capacitor values, do not confuse the manufacturing
codes with the component value. If it looks strange, it may be a manufacturing
code, look on the other side of the component.
Be sure you have read the values correctly. Sort all the capacitors out before
you start assembling them onto the modules. They are difficult to remove and
correct.
L1 molded inductors look like a resistors, but are fatter. With an ohm meter, will read 0 ohms.
40M
[ ] L1 – 2.2 uH – Red/Red/Gold/Gold or Red/Red/Gold/Silver
[ ] C26 – 100 pfd – marked 101
[ ] C27 – 22 pfd – marked 22 or 220
[ ] C28 – 22 pfd – marked 22 or 220
[ ] C29 – 330 pfd – marked 331
[ ] C30 – 680 pfd – marked 681
[ ] C31 – 68 pfd – marked 68 or 680 (don't mix up the 681 and 68 values!)
[ ] C32 – 330 pfd – marked 331
[ ] L2 – 20 turns on T37-2 RED core – make sure turns are snug to the core and more or less
evenly spaced around the core. Loose winding does not work well.
[ ] L3 – 18 turns on T37-2 RED core
[ ] X1 – 7.074 MHz crystal. If you are not using the optional VFO, you need to jumper the
“CRYSTAL ENABLE” pads with a clipped piece of a resistor lead. Otherwise omit the jumper for
VFO operation.
30M
[ ] L1 – 1.2 uH – Brown/Red/Gold/Gold or Brown/Red/Gold/Silver
[ ] C26 – 100 pfd – marked 101
[ ] C27 – 22 pfd – marked 22 or 220
[ ] C28 – 22 pfd – marked 22 or 220
[ ] C29 – 220 pfd – marked 221
[ ] C30 – 560 pfd – marked 561
[ ] C31 – 47 pfd – marked 47 or 470
[ ] C32 – 220 pfd – marked 221
[ ] L2 – 18 turns on T37-2 RED core – make sure turns are snug to the core and more or less
evenly spaced around the core. Loose winding does not work well.
[ ] L3 – 13 turns on T37-2 RED core
[ ] X1 – 10.136 MHz crystal. If you are not using the optional VFO, you need to jumper the
“CRYSTAL ENABLE” pads with a clipped piece of a resistor lead. Otherwise omit the jumper for
VFO operation.

Page 9 of 16 ft8_II_assy_smd_diode_072020.pdf
20M
[ ] L1 – 0.68 uH – Blue/Gray/Silver/Gold or Blue/Gray/Silver/Silver
[ ] C26 – 100pfd – marked 101
[ ] C27 – 22 pfd – marked 22 or 220
[ ] C28 – 22 pfd – marked 22 or 220
[ ] C29 – 150 pfd – marked 151
[ ] C30 – 330 pfd – marked 331
[ ] C31 – 33 pfd – marked 33 or 330 (don't mix up the 331 and 33 values!)
[ ] C32 – 150 pfd – marked 151
[ ] L2 – 17 turns on T37-2 YELLOW core – make sure turns are snug to the core and more or less
evenly spaced around the core. Loose winding does not work well.
[ ] L3 – 15 turns on T37-2 YELLOW core
[ ] X1 – 14.074 MHz crystal. If you are not using the optional VFO, you need to jumper the
“CRYSTAL ENABLE” pads with a clipped piece of a resistor lead. Otherwise omit the jumper for
VFO operation.
Winding the toroids:
[ ] Wind each of the L2 and L3 toroids using 12” of the supplied magnet wire. Use the tables
above and wind them in the direction shown in the graphic below and they will align with the pcb
holes. When you are certain of the turn count, trim the leads ~3/8” and tin them before installing
the toroids flat on the top of the board, centered on the silkscreen outline. Secure each toroid to
the pcb using two of the supplied plastic zip ties, as shown below.
Be sure to tin the wire ends before installing. The transceiver will not work if you do not
tin the magnet wire. This is a leading cause of failure. Be sure not to pull the wire thru
the hole past where you have it tinned.
Test and set up:
[ ] Apply 12V to 13.8V to the board.
[ ] Verify 9V (+/- 0.25) between pins 8 and 4 of U2. (Optional)
[ ] Remove power
[ ] Install LM358 IC into U2 socket.
The following bias adjustment is made without a band module or optional vfo attached.
[ ] Connect your DMM in series with the positive power supply lead and set the meter to measure
current. To be safe, use the 10A scale.
[ ] Set the V1 (BIAS) trimmer to fully Clockwise.
[ ] Apply power to the board again.
[ ] Insert the shorting jumper (Berg connector) into the [TEST] SIP pins. This will force the board
into transmit mode. The RED LED should now be on.
[ ] Note the amount of current the board is drawing.
[ ] Slowly adjust the V1 trimmer Counterclockwise while watching the current meter. Adjust
until the current GOES UP by about 15 ma. This is just enough to put the PA into linear mode.
[ ] Remove power
[ ] Remove the shorting plug from the [TEST] pins.

Page 10 of 16 ft8_II_assy_smd_diode_072020.pdf
You are now ready for on-air testing.
[ ] Start the WSJT-X program on your PC or Laptop.
[ ] Make the required MIC and Headphone connections between the PC and DSB board. MIC to
MIC and PHONES to PHONES. (I found nice stereo jumper cables at the Dollar Store).
[ ] Plug in the desired band module. The component side of the board faces you, the end with the
LED. Use the band module with the crystal.
[ ] If using the VFO, be sure to remove the crystal enable jumper and set the VFO to the desired
band and frequency.
[ ] Connect up your antenna.
[ ] Power up the board.
[ ] If the band is open, you should start to see signals. Adjust the Sound card input level and the
V2 audio output level to appropriate settings for your conditions.
[ ] Replace the antenna with a 50 ohm dummy load.
[ ] Set the sound card output level to minimum.
[ ] Activate FT8 transmit in the program.
[ ] Increase sound card output level until the board switches into Transmit. (RED LED goes on)
you can continue to increase the output level a little bit to ensure reliable
triggering of the VOX circuit.
If you have a watt meter in line with the antenna, you will notice the power will
continue to increase as the audio input continues to increase. Do not do this. The
apparent increase in power is due to overloading the mixer and amplifier stages,
putting them into a non-linear region.
As you see below, if you look at the RF output with an oscilloscope, it should look like a string of
pearls. This is the result of the two side bands mixing. Increasing the drive will turn the string of
pearls into more of a picket fence and then approach being a wall. This is the result of the
amplifier stages saturating, resulting in the signal flat topping creating spurious outputs to the
annoyance of others in the band. Always keep your signal clean. We're transmitting on two side
bands.
[ ] Reconnect the antenna and you are good to go.
Refer to the WSJT-X documentation and our website links for more details on operation.

Page 11 of 16 ft8_II_assy_smd_diode_072020.pdf
Theory of operation:
The Digital DSB transceiver is built around the ubiquitous SA602/612A mixer-oscillator chip. It
provides both the receive and transmit functions.
Receiver:
The antenna is first routed through the transmitter's Low Pass Filter (LPF) and then into a BS170
MOSFET, which is the receiver input T/R switch. The received signal is coupled into a new High
Pass Filter (HPF) circuit comprised of C26 and L1. Stray capacitance (~88pF) resonates L1 to
about the operating frequency.
The received input signal is applied to the input of the SA602 mixer (U1) to produce the base line
audio output. The Local Oscillator is either the crystal on the band module using the internal
oscillator of the SA602, or an optional Digital VFO.
U2b, one half of a LM358 op amp, provides audio gain for decent sensitivity. A non-inverting
configuration is used so that the input can be high impedance, allowing for reasonably small value
input coupling caps. The gain is set to 47. The amplifier then drives an audio level pot so the
audio level can be adjusted to a level suitable for your PC sound card. Q1 provides muting of the
audio output by shorting the input to the audio level pot to ground.
Transmitter:
The SA602/612 requires very little input signal to saturate. Therefore a resistor divider is placed
between the audio input from the sound card to the mixer input. This allows you to set the audio
output from the sound card to a reasonable level and not overdrive the mixer.
The other half of the LM358 (U2a) is used as a VOX circuit. The peak detector circuit of D3 and
C12 isn't required for FT8 operation, but is included if one wishes to experiment with other modes
where the audio input can drop to zero for short periods of time.
The output of the Peak Detector activates the T/R switching.
 Q4 turns on, activating this sequence:
 Q2 is turned off, which disconnects the antenna from the mixer input.
 Q5 is turned on, which switches on the power to the transmit circuits.
 Q1 is turned on, muting the audio output.
 Q3 is turned on, shunting any transmit RF which might leak through Q1.
Q6-Q7-Q8 amplifies the RF output from the mixer to a level sufficient to drive the PA. The PA is
comprised of three BS170 MOSFETS in parallel. Bias is applied to the gates to place the amplifier
into linear mode. This also reduces the amount of drive needed since the input signal does not
have to first exceed the ~2.5V it takes to start to turn on the MOSFETS. The signal then goes to
the Low Pass Filter (LPF) and finally the antenna.
Power to the circuits is supplied by a 9V, 1A regulator. This ensures the power output remains in a
safe operating area and if there is a problem, the internal over current protection will shut down
the regulator. Since the maximum operating voltage of the SA602/612 is 9V, a diode is placed in
series with the 9V supply insure the voltage to the chip does not exceed the maximum
recommended supply voltage.

Page 12 of 16 ft8_II_assy_smd_diode_072020.pdf
Trouble shooting:
Soldering issues are the most common reason for a board not to work the first time. A careful
visual inspection will often locate the problem. Ground pads take a little extra heat compared to
other pads, so take note of these. Solder can stick to the component lead, but not flow into the
hole. These bad connections can be hard to spot.
Another problem area is the tinning of the magnet wire used to wind the cores. The wire should
have been tinned before you tried to solder the leads to the board, but sometimes the wire gets
pulled in past the tinned area so the solder doesn't real stick or makes an intermittent connection.
The bifilar wound cores should have continuity between all four pads if the wires are in the right
place. If the pair is reversed, there will only be continuity between the two pads on opposite sides
of the core. If you cannot adjust the PA bias, it is likely T2 is not installed correctly or has a
soldering issue.
Did you do the continuity check of soldering U2?
Double check resistor locations. Make sure you didn't mix up values with similar color codes.
The voltage chart on page 12 can be useful to narrow down a problem area. The exact voltage will
vary a little a little depending on component tolerances and your meter. Only be concerned if the
voltages are significantly different than those shown.
Almost all of the construction issues with the DSB transceiver have been traced to the faulty
installation of T1 or T2. Check carefully the correct orientation of the primary, secondary, tinning
and final soldering of the toroid leads. Double check the T1 and T2 continuity check described
earlier.
VOX/switching problems:
To test the vox circuit there must be enough audio from the sound card. Check that the computer
is outputting audio to J3. The vertical slider marked (Pwr) on the right side of the WSJT-X
program is the output from the sound card. Moving the slider up should put the transceiver into
transmit, illuminating the LED. In order for the transceiver to enter into transmit mode and the TX
LED to come on, Q5 has to be biased “ON” through R3 and Q4. Q4 turns on when it’s gate is
biased to about 2V. The gate of Q4 is biased to about 2V when the output of U2a (pin1) goes
above about 2.4V. This should take a minimum of 37 mV in respect to ground on Pin 2.
So, where does this go wrong?
Is Pin 1 of U2 high or low?
 Low – no problem
 High – (~8.5V) check resistors R15, R17, R18 for cold solder connections. Check U2 socket
lead connections to board.
 Gate of Q4 high, but Pin 1 low? Check for short across jumper pins and or connection to R7
bad.
 Gate of Q4 low, Drain also low? Q4 defective. Verify short with ohm meter.
 Gate of Q4 low, Drain high? Q5 Shorted.
 Check C11 polarity. If backwards, the cap leakage would trigger U2.

Page 13 of 16 ft8_II_assy_smd_diode_072020.pdf
X-ray view of board. “floating” pads are connected to ground plane, not shown for clarity.
D=Drain G=Gate S=Source E=Emitter B= Base C=Collector I=Input G=Ground O=Output
Pin 1 2 3 4 5 6 7 8
U1 1.42 1.42 0 7.15 7.15 8.3 7.5 8.35
U2 Rx 0 0 0 0 4.5 4.5 4.5 9
Rx D / C G / B S / E Tx D / C G / B S /E
Q1 0V 0V 0V 0V 9V 0V
Q2 0V 9V 0V 0V 0V 0V
Q4 9V 0V 0V 0V 9V 0V
Q6/7/8 9V 0V 0V 9V ~2.5V 0V
Q3 0V 0V 0V 0V 0.78V 0V
Q5 0V 9V 9V 8.8V 8.15V 9V

Page 14 of 16 ft8_II_assy_smd_diode_072020.pdf

Page 15 of 16 ft8_II_assy_smd_diode_072020.pdf

Page 16 of 16 ft8_II_assy_smd_diode_072020.pdf
In the table below are some “modeled” values for additional bands to experiment with. Some
tweaking may be required. You will need to source your own components. If you choose to model
your own high pass filter (L1 & C26), be sure to add the 88pF stray capacitance inherent in the
design to C26. That has been done with the modeling you see below.
Notes:
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