Kanga Products FOXX-3 User manual

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
The FOXX-3
20m QRP
TRANSCEIVER
In the summer 1983 issue of SPRAT, the journal of the G-QRP Club, there appeared a design for an elegantly simple
QRP transceiver called the Foxx. Designed by George Burt GM3OXX, the Foxx used just five transistors and employed
the PA transistor as the detector for the receiver.
The FOXX-3 by Derek Alexander G4GVM was published in the spring 1999 issue
of SPRAT. While based on the original FOXX, it had a few refinements to make
operation easier: Automatic transmit/receive change over (semi-break-in),
sidetone and built in harmonic filter. Derek has kindly given Kanga Products
permission to produce the FOXX-3 in kit form.
This kit contains a high quality fibreglass printed circuit board with component
positions printed in white, all board mounted components, a power cable and
detailed step by step instructions. To build the kit you will need a soldering iron, solder, wire cutters and fine tipped
pliers. To operate the FOXX-3 transceiver you will need a pair of headphones, 12v DC supply (a battery is ideal) and
antenna a tuning unit for the 20m Band. A power meter would be useful to. A separate Morse key can be used, but
a board mounted key is provided.
The FOXX-3 printed circuit board has been designed to give the constructor a number of choices:
1. Enclosure.
a. The board can be fitted into an ‘Altoids’™ mint tin. All connections are made vertically from the board so
the transceiver is concealed when the lid is closed. Mounting screws may be fitted through holes drilled
into the floor of the tin. Alternatively the board maybe carried in the tin and removed for operation.
b. The board may be secured to a chassis using screws through the 3.2mm holes provided. Sizes 6BA, ISO
3mm and 4-40 UNC are suitable.
2. Headphone connection (Low impedance “personal stereo type).
a. 3.5mm Mono or stereo Jack plug (track break needed if using mono plug).
b. 2-pin 0.1” header plug.
3. Morse Key or Keyer connection.
a. 3.5mm Jack plug, sleeve connected to 0v
b. 2-pin 0.1” header plug
c. S small push button (supplied) maybe fitted directly to the board.
If you intend to mount the board on screws, use it as a template to mark the hole positions before any
components are soldered in place.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
The Kanga Products FOXX-3 20m QRP Transceiver
Assembly Instructions
Stage 1: The audio amplifier
The FOXX-3 audio amplifier is an LM386 integrated circuit, IC1. It has two inputs with separate volume controls, one
for the receiver audio and on for the transmitter sidetone. During transmission a transistor mutes the receiver audio
input. The amplifier’s output drives low power impedance mono or stereo headphones via a 3.5mm jack socket. The
headphones used with personal stereo players are suitable. If a mono jack is used, a small track cut is necessary to
prevent audio signal being short-circuited to ground. See diagram on the following page. Alternatively a 2 pin header
plug and socket (supplied) can be fitted instead of the jack socket.
Referring to the diagrams on the following page, fit and solder the audio amplifier components in the positions
marked on the component side of the board. The electrolytic capacitors C1, C3, C6 and C9 have a negative and a
positive lead and must be connected the correct way round otherwise they may be damaged when power is applied.
The negative lead is shorter as supplied and is marked with a minus (-) sign on the body of the capacitor. This lead
goes through the hole marked with a minus sign and is soldered to the square pad.
Part
Type
Markings
Notes
R1
100Ω
Brown, Black, Brown, Gold
R2
10KΩ
Brown, black, Orange, Gold
R3
10Ω
Brown, Black, Black, Gold
VR1
47KΩ
47K
Gently push the spindles into the
VR2
1KΩ
1K
central holes of these after soldering.
IC Socket
Fit in position marked IC1 with notch
towards lower edge of the board.
C1
100µF
100µF 16v
Electrolytic capacitor - observe polarity
C2
100nF
104
C3
100µF
100µF 16v
Electrolytic capacitor - observe polarity
C4
100nF
104
C5
100nF
104
C6
10µF
10µF 16v
Electrolytic capacitor - observe polarity
C7
100nF
104
C8
10nF
103
C9
100µF
100µF 16v
Electrolytic capacitor - observe polarity
C10
100nF
104
CON1
2-pin plug
Fit with plastic tab near edge of board
CON2
3.5mm Jack socket or 2-pin plug
Use the connector you prefer
IC1
LM386
LM386
Fit into IC socket with notch
towards lower edge of board.
It is important to fit CON1 as shown otherwise the power supply connections will be reversed.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
Inspection
Before connecting power to the board, examine each component and check that it is right part in the right place,
then turn the board over and examine each solder joint. Check that there are no solder splashes joining tracks. Once
you are sure that all is well the board may be tested.
Testing the Audio Amplifier
Connect headphones to CON2 and a 12v DC power supply to CON1 using the lead supplied (red to positive, black to
negative. Turn the spindles of the volume and side tone controls fully clockwise. Holding the headphones some
distance from your ears, touch the upper terminal of the volume control with a metal object such as a screwdriver.
You should hear a buzzing noise in the headphones (assuming you are near a mains supply) Now touch the upper
terminal of the sidetone control and observe a similar buzzing noise. Turn the two spindles fully anticlockwise and
repeat the test. This time there should be no buzzing noise.
If you hear no sound during this test, disconnect the power supply immediately and re-examine your work for errors,
missed solder joints and solder splashes. Check that the LM386 is fitted the right way round. Check the headphones
on a radio or other equipment, they maybe faulty.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
The Kanga Products FOXX-3 20m QRP Transceiver
Assembly Instructions
Stage 2: The keying circuit
When the FOXX-3’s Morse key is pressed several things happen. Transistor TR2 turns on, energising the relay> This
removes the positive supply fed to the crystal oscillator via the Rx offset control, and disconnects the detector (PA
Transistor) from the volume control. Transistor TR1 turns on, energising the key +12v rail. This applies power directly
to the crystal oscillator (not via the offset control) to the PA transistor and to the sidetone oscillator so that the
Morse code being transmitted can be heard in the headphones. The voltage across the relay coil turns on TR3 to
mute the audio amplifier’s receiver input. When the key is released between the elements of Morse characters (Dits
and Dahs), the sidetone oscillator and crystal oscillator stop running but the relay is kept energised by the charge on
capacitor C13. If the key remains released for more than about half a second, the relay contacts change back to the
receive position. This time can be adjusted by altering the value of R6. The charge on C15 holds the mute transistor
on until the relay contacts have changed over.
Part
Type
Markings
Notes
R4
1KΩ
Brown, Black, Red, Gold
R5
4k7Ω
Yellow, Violet, Red, Gold
R6
10KΩ
Brown, Black, Orange, Gold
R7
100KΩ
Brown, Black, Yellow, Gold
R8
1KΩ
Brown, Black, Red, Gold
C11
100nF
104
C12
100nF
104
C13
10µf
10µF 16v
Electrolytic Capacitor-Observe polarity
C14
100nF
104
C15
10µf
10µF 16v
Electrolytic Capacitor-Observe polarity
C16
10nF
103
C17
100nF
104
D1
1N4148
1N4148
Diode - Observe polarity
D2
1N4148
1N4148
Diode - Observe polarity
D3
1N4148
1N4148
Diode - Observe polarity
TR1
BC327
BC327
Transistor –Observe polarity
TR2
BC212
BC212
Transistor –Observe polarity
TR3
BC182
BC182
Transistor –Observe polarity
RELAY
12v DPDT
CON3
3.5 Jack Socket or 2 Pin Molex plug
Your choice
SW1
Maybe fitted instead of CON3
Straighten pins of SW1 before fitting
As with the audio amplifier stage, inspect your work before testing.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
Testing the keying circuit.
Turn both the volume control and the sidetone control full anticlockwise. Connect a Morse key to CON3 (unless you
have fitted the switch to the board) and a 12v supply to CON1. Press the Morse key or switch. The relay should give a
click as it pulls in (energises). Release the key and note that there is a short delay before the relay clicks again as it
drops out (de-energises). Now connect the headphones to CON2. Touch the upper terminal of the volume control
with a metal object as before and turn the volume control clockwise until the buzzing noise is heard. Press the Morse
key and observe that the buzzing noise is muted. Release the key and observe that the bussing noise returns when
the relay drops out.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
The Kanga Products FOXX-3 20m QRP Transceiver
Assembly Instructions
Stage 3: The sidetone circuit.
When the FOXX-3’s Morse key is pressed the transmitter emits a radio frequency signal and the sidetone oscillator
produces a tone which is heard in the headphones. This sidetone enables the operator to monitor his or her own
sending. In the FOXX-3 the sidetone is produced by a phase shift audio oscillator TR4 fed from the keyed +12v line.
Its output goes to the second input of the LM386 via a separate volume control VR2.
Part
Type
Markings
Notes
R9
47KΩ
Yellow, Violet, Orange, Gold
R10
4K7Ω
Yellow, Violet, Red, Gold
R11
10KΩ
Brown, Black, Orange, Gold
R12
10KΩ
Brown, Black, Orange, Gold
R13
10KΩ
Brown, Black, Orange, Gold
R14
680Ω
Blue, Slate, Brown, Gold
R15
4M7Ω
Yellow, Violet, Green, Gold
C18
10nF
103
C19
10nF
103
C20
10nF
103
C21
1µF
1µF 50v
Electrolytic Capacitor-Observe polarity
C22
100nF
104
TR4
BC182
BC182
Transistor-Observe polarity
The components in this area of the board are very densely packed. Check the position of each
Component carefully before soldering.
Inspect your work before testing.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
Testing the sidetone circuit.
Turn both the volume control and the sidetone control fully anticlockwise. Connect a Morse key to CON3 (unless you
have fitted the switch to the board), headphones to CON2 and a +12v supply to SK1. Press the Morse key or switch.
Turn the sidetone control clockwise until a musical note can be heard in the headphones. Adjust the volume control
to a comfortable level using the sidetone control. Release the Morse key and notice that the sidetone stops
immediately.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
The Kanga Products FOXX-3 20m QRP Transceiver
Assembly Instructions
Stage 4: The crystal oscillator.
The operating frequency is determined by a quartz crystal in an oscillator circuit built around TR5. The trimmer
capacitor TC1 allows a frequency variation of about 6kHz in the 20m band. During transmission the oscillator is fed
from the keyed +12v line via diode D4. During reception it is fed continuously via a variable resistor VR3, which
allows the frequency to be offset by a few hundred hertz. When another station replies to the FOXX-3 on exactly the
same frequency (zero beat) this offset produces an audible tone (beat note) in the headphones.
After soldering the crystal in place it should be made more secure by soldering a stiff wire (such as one trimmed
from a resistor) from the top of the crystal to the earth track through the adjacent hole provided. Work quickly to
avoid unnecessarily over heating the crystal.
Resistor R17 determines the collector current of the oscillator transistor, the amount of drive applied to the PA
transistor and so the output power of the transmitter. It is marked AOT (Adjust On Test) on the board. The two
terminal pins provided should be pushed through the holes for R17 from the track side of the board and their heads
soldered to the copper pads. R17 can then be soldered to the pins on the component side of the board, and maybe
changed for a different value even if the board is screwed down into a case. Start with the resistor supplied. When
the PA stage is fitted, adjust the value of R17 if necessary to give 800mW to 1 W output.
Part
Type
Markings
Notes
R16
100KΩ
Brown, Black, Yellow, Gold
R17
220Ω
Red, Red, Brown, Gold
Adjust on test
VR3
4K7Ω
4K7
Gently push spindle into
the central hole after soldering
TC1
5.5 - 65pF
None
Yellow plastic 3 Lead Component
C23
100nF
104
C24
100pF
n10
C25
------
Not used in 20m Version
L1
2.2mH
Red, Red, Red, Gold
XTAL
14.060MHz
14.0600
TR5
BC182
BC182
Transistor-Observe polarity
D4
1N4148
1N4148
Diode-Observe polarity
Examine board for errors, solder splashes, etc. Before testing.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
Testing the crystal Oscillator
Tune a shortwave receiver or transceiver to the operating frequency of the FOXX-3 marked on the crystal. Set the
mode switch to CW or USB. Connect the 12 volt supply to the FOXX-3 and search for the crystal oscillator’s signal on
the receiver. Turn the trimmer capacitor’s spindle using an insulated tool and observe the frequency shift. Set the
capacitor to middle of its tuning range. Turn the Rx offset control VR3 fully clockwise.
Press and hold the Morse key on the FOXX-3 and re-tune the receiver until the pitch of the note is comfortable for
reading Morse. This is usually between 400 and 800 Hz; use the FOXX-3’s sidetone pitch as a guide. Release the
Morse key and turn the Rx offset control anticlockwise, noting the rise in pitch of the signal on the receiver. Adjust
the offset control until the pitch is one octave higher, if possible, than the key-down pitch. (Think of the first two
notes of the song “Somewhere over the rainbow”. In the 80m version it may not be possible to achieve this amount
of offset.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
The Kanga Products FOXX-3 20m QRP Transceiver
Assembly Instructions
Stage 5: The power amplifier and filter.
In the FOXX series of transceivers the power amplifier (PA) transistor also functions as the receiver mixer. In the
FOXX and FOXX-2 the changeover was made with a switch. The FOXX-3 uses a relay to give semi-break-in keying. The
PA transistors collector is coupled to the antenna via a low pass filter. The base is driven by the crystal oscillator. The
emitter is connected by the relay to the volume control on receive and to the keyed +12v line on transmit.
Inductors L3, 4 and 5 are wound on toroid (ring) cores. L2 a ferrite bead, but the winding method is the same for
both types. L2 is wound with 14 turns of the thinner wire supplied in the stage 5 packet. The diagram on the
following page shows the appearance of a wound toroid. The number of turns on the coil equals the number of
times the wire passes through the central hole. In the case of L3, 4 and 5 using the thicker wire supplied, the turns
should be evenly spaced, not over lapping, with a gap between the first and last turn as shown. Wind these in the
direction shown so that the wires line up with the holes in the board.
When the winding is complete, trim the wires to a length of around 10mm measured from the edge of the toroid. To
tin the end of the wires, form a bead of molten solder on the tip of the soldering iron and pass the end of the wire
through it. After a few seconds the enamel will melt and the solder will wet the wire. Add more solder until the wire
is properly tinned. Avoid breathing in the fumes produced when soldering enamelled wire.
Solder all the components into place, press the heat sink onto TR6 and examine all solder joints before testing the
completed transceiver. NOTE: The BNC socket remains hot for a long time after soldering.
Part
Type
Markings
Notes
C26
100nF
104
C27
100nF
104
C28
180pF
180p
If possible, polystyrene capacitors
C29
390pF
390p
will be supplied for C28 to C31.
C30
390pF
390p
If they are not available, ceramic
C31
180pF
1800p
capacitors will be supplied instead.
TR6
2N2905A
2N2905A
L2
14 turns
Ferrite bead
Use the thinner wire for L2
L3
16 turns
Yellow Toroid
Use the thicker wire for L3, 4 and 5
L4
17 turns
Yellow Toroid
L5
16 turns
Yellow Toroid
CON4
Vertical BNC Socket

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
Testing the power amplifier and filter.
Connect a power meter to the antenna socket CON4 and the 12 volt supply to CON1. Press the Morse key and
measure the output power. This should be between 500 milliwatts and 1 watt. The power can be altered by changing
R17, the resistor soldered to the pins. Reducing the value of R17 will increase the power. Do not run the FOXX-3 with
a power output above 1 watt. It may be necessary to readjust the receiver offset as described in the previous stage.

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk

©Kanga Products 2001 –2016 All rights reserved www.kanga-products.co.uk
Using the FOXX-3 20m transceiver.
The FOXX-3 is designed to match a 50Ωunbalance antenna feeder. A suitable antenna tuner should be used. Do not
operate the FOXX-3 without a load connected to the antenna socket.
Because the PA transistor is driven as the detector during reception, a few microwatts of power will be radiated at
this time. This is normal, but if monitored on another nearby receiver it gives the impression that a strong carrier is
being radiated all the time. In practice this should not cause interference to other stations, because it is at a very low
level.
The output filter is effective at suppressing harmonic radiation. On test sample in the Kanga Lab, all harmonic
radiation was better that 46dB below carrier level.
When using the FOXX-3 it should be remembered that it is a very simple transceiver, which lacks the selectivity of
complex designs. It has an audio image, which means that it cannot discriminate between station above and below
its operating frequency. If for example, the FOXX-3’s oscillator is tuned to 14.060 000 MHz when in receive mode,
stations on 14.060 800 MHz and 14.059 200 will both produce 800Hz beat notes in the headphones.
The FOXX-3 can be operated from any DC supply of 9 to 14 volts. It draws around 250mA when transmitting, so a
small 12 volt sealed acid battery makes a good power supply once the transceiver has been tested. Do not use such a
battery for initial tests as these can deliver enormous currents and may damage the FOXX-3 if any construction
errors have been made. Connect a 1 amp fuse in the positive lead as near to the battery as possible. When a direct
conversion receiver such as that in the FOXX-3 is used with a mains power supply a humming noise is often heard
from the receiver. This is caused by RF energy from the oscillator entering the power supply wiring and being
detected by the rectifier. The hum can usually be cured by careful filtering.
We hope you will enjoy building and using the FOXX-3. If you have any questions or suggestions for improvements to
the kit or instructions, please contact us.