QRPKits BITX20A Manuel utilisateur
Hendricks QRP Kits
BITX20A to BITX17A
Conversion Instructions
30 November 2008
Converting your BITX20A Kit to a BITX17A Kit is not all that complex. It only requires that you
change crystals and some resonance components to values used in the BITX17A design. The basic
design for both 20 meters and 17 meters is the same, thus DC voltages and troubleshooting methods
remain the same except for obvious frequency differences.
There is a BITX discussion group available at: http://groups.yahoo.com/group/BITX20/
Doug Hendricks KI6DS web site for kit sales is at: http://www.qrpkits.com
Farhan's original BITX20 design web site is at: http://www.phonestack.com/farhan/bitx.html
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Your BITX20A to BITX17A Conversion Kit will include a decal sheet, crystals, inductors, and various
capacitors needed for the conversion.
You will be removing installed components (unless your are converting an as-yet
unfinished BITX20 kit) and installing replacement components in their place. Some
care is required to avoid damaging the PCB in the un-soldering and re-soldering
process. Solder wick (or a section of braid salvaged from a length of coaxial cable
shield) helps to remove excess solder, as does a spring-driven “solder sucker” tool.
The round type of wooden toothpicks can also be used to push through heated holes
where components have been removed. This opens the holes for installation of new
components.
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Conversion Parts List:
Part Number 17 Meter Parts 20 Meter Parts Part Description
X-1 12.96 MHz 11.0 MHz Crysta
X-2 12.96 MHz 11.0 MHz Crysta
X-3 12.96 MHz 11.0 MHz Crysta
X-4 12.96 MHz 11.0 MHz Crysta
X-5 12.96 MHz 11.0 MHz Crysta
L-10 1.0 uH 1.2 uH Mo ded Choke
L-5 6.8 uH 8.2 uH Mo ded Choke
C-92 51 pf 68 pf Ceramic Capacitor
C-54 68 pf 82 pf Ceramic Capacitor
C-55 82 pf 100 pf Ceramic Capacitor
C-56 82 pf 100 pf Ceramic Capacitor
C-47A 82 pf 100 pf Ceramic Capacitor
C-47B 82 pf 100 pf Ceramic Capacitor
C-48A 150 pf 180 pf Ceramic Capacitor
C-48B 150 pf 180 pf Ceramic Capacitor
C-49A 82 pf 100 pf Ceramic Capacitor
C-49B 82 pf 100 pf Ceramic Capacitor
C-34 390 pf 470 pf Po ystyrene Cap
C-35 390 pf 470 pf Po ystyrene Cap
C-37 130 pf 220 pf Po ystyrene Cap
C-11 8.2 pf 10 pf Ceramic Capacitor
C-13 68 pf 82 pf Ceramic Capacitor
C-15 120 pf 180 pf Ceramic Capacitor
C-16 10 pf 8.2 pf Ceramic Capacitor
C-17 47 pf 56 pf Ceramic Capacitor
C-19 8.2 pf 10 pf Ceramic Capacitor
C-20 68 pf 82 pf Ceramic Capacitor
C-24 6.8 pf 8.2 pf Ceramic Capacitor
C-25 68 pf 100 pf Ceramic Capacitor
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Parts Placement Diagram:
( Drawing by KD1JV )
Page 4 of 34
BITX17A Schematic Diagram:
( Drawing by N7VE )
Page 5 of 34
Conversion Steps
Now might be a good time to check R-2. R-8, R-83, and R-91 to insure that they
are turned totally counter-clockwise. This is to make sure that the transmitter
RF drive level is at minimum, and that the MOSFET bias levels are also at
minimum. During the alignment procedure you will readjust these
potentiometers to their proper levels.
BFO Components:
[ ] Remove L-5 (8.2 uh molded inductor) marked Gray-Red-Gold-Gold
[ ] Install new L-5 (6.8 uh molded inductor) marked Violet-Gray-Gold-Gold
[ ] Clip excess lead length.
[ ] Inspect solder connections.
[ ] Remove X-5 (11 MHz Crystal)
[ ] Install new X-5 (12.96 MHz Crystal)
NOTE: Before you install the new crystal for X-5, you may want to temporarily
insert each new 12.96 MHz crystal into the BFO oscillator position (X-5) and
measure the default frequency for each crystal (measure BFO frequency at the top
of R-67). Mark each crystal with it's frequency. Now select the 4 crystals which
are closest in frequency for use in X-1, X-2, X-3, and X-4. The remaining 12.96
MHz crystal will be your X-5 crystal for the BFO oscillator. While not absolutely
necessary, this procedure may provide steeper sidebands on your crystal filter than
would a random selection of crystals.
[ ] Remove X-1 (11 MHz Crystal)
[ ] Install new X-1 (12.96 MHz Crystal)
[ ] Remove X-2 (11 MHz Crystal)
[ ] Install new X-2 (12.96 MHz Crystal)
[ ] Remove X-3 (11 MHz Crystal)
[ ] Install new X-3 (12.96 MHz Crystal)
[ ] Remove X-4 (11 MHz Crystal)
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[ ] Install new X-4 (12.96 MHz Crystal)
[ ] Clip excess lead length.
[ ] Inspect solder connections.
VFO Blocking Filter (L-10 & C-25):
[ ] Remove L-10 (1.2 mh molded choke)
[ ] Install new L-10 (1.0 mh molded choke)
[ ] Remove C-25 (100 pf Ceramic Capacitor)
[ ] Install new (C-25 (68 pf Ceramic Capacitor)
[ ] Clip excess lead length.
[ ] Inspect solder connections.
[ ] Remove C-92 (68 pf Ceramic Capacitor)
[ ] Install new C-92 (51 pf Ceramic Capacitor)
[ ] Remove C-54 (82 pf Ceramic Capacitor)
[ ] Install new C-54 (68 pf Ceramic Capacitor)
[ ] Remove C-55 (100 pf Ceramic Capacitor)
[ ] Install new C-55 (82 pf Ceramic Capacitor)
[ ] Remove C-56 (100 pf Ceramic Capacitor)
[ ] Install new C-56 (82 pf Ceramic Capacitor)
[ ] Clip excess lead length.
[ ] Inspect solder connections.
[ ] Remove C-47A (100 pf Ceramic Capacitor)
[ ] Install new C-47A (82 pf Ceramic Capacitor)
[ ] Remove C-47B (100 pf Ceramic Capacitor)
[ ] Install new C-47B (82 pf Ceramic Capacitor)
[ ] Remove C-48A (180 pf Ceramic Capacitor)
[ ] Install new C-48A (150 pf Ceramic Capacitor)
Page 7 of 34
[ ] Remove C-48B (180 pf Ceramic Capacitor)
[ ] Install new C-48B (150 pf Ceramic Capacitor)
[ ] Remove C-49A (100 pf Ceramic Capacitor)
[ ] Install new C-49A (82 pf Ceramic Capacitor)
[ ] Remove C-49B (100 pf Ceramic Capacitor)
[ ] Install new C-49B (82 pf Ceramic Capacitor)
[ ] Clip excess lead length.
[ ] Inspect solder connections.
[ ] Remove C-34 (470 pf Polystyrene Capacitor)
[ ] Install new C-34 (390 pf Polystyrene Capacitor)
[ ] Remove C-35 (470 pf Polystyrene Capacitor)
[ ] Install new C-35 (390 pf Polystyrene Capacitor)
[ ] Remove C-37 (220 pf Polystyrene Capacitor)
[ ] Install new C-37 (130 Polystyrene Capacitor)
[ ] Clip excess lead length.
[ ] Inspect solder connections.
[ ] Remove C-11 (10 pf Ceramic Capacitor)
[ ] Install new C-11 (8.2 pf Ceramic Capacitor)
[ ] Remove C-13 (10 pf Ceramic Capacitor)
[ ] Install new C-13 (8.2 pf Ceramic Capacitor)
[ ] Remove C-15 (180 pf Ceramic Capacitor)
[ ] Install new C-15 (120 pf Ceramic Capacitor)
[ ] Remove C-16 (10 pf Ceramic Capacitor)
[ ] Install new C-16 (8.2 pf Ceramic Capacitor)
[ ] Remove C-17 (56 pf Ceramic Capacitor)
Page 8 of 34
[ ] Install new C-17 (47 pf Ceramic Capacitor)
[ ] Clip excess lead length.
[ ] Inspect solder connections.
[ ] Remove C-19 (10 pf Ceramic Capacitor)
[ ] Install new C-19 (8.2 pf Ceramic Capacitor)
[ ] Remove C-20 (82 pf Ceramic Capacitor)
[ ] Install new C-20 (68 pf Ceramic Capacitor)
[ ] Remove C-28 (8.2 pf Ceramic Capacitor)
[ ] Install new C-28 (6.8 pf Ceramic Capacitor)
[ ] Clip excess lead length.
[ ] Inspect solder connections.
[ ] Remove L-7 (VFO Oscillator Coil) Remove 14 turns. This should leave 36 turns on
the core.
[ ] Re-install L-7
[ ] Remove L-6 (RF Filter Coil) Remove 4 turns. This should leave 14 turns on the core.
[ ] Re-install L-6
[ ] Remove L-4 (RF Filter Coil) Remove 4 turns. This should leave 14 turns on the core.
[ ] Re-install L-4
[ ] Clip excess lead length.
[ ] Inspect solder connections.
[ ] Remove L-1 (Antenna Filter) Remove 3 turns. This should leave 9 turns on the core.
[ ] Re-install L-1
[ ] Remove L-2 (Antenna Filter) Remove 3 turns. This should leave 9 turns on the core.
[ ] Re-install L-2
[ ] Clip excess lead length.
[ ] Inspect solder connections.
Page 9 of 34
Congratulations. You have completed converting your BITX20A to a BITX17A, and are ready to
proceed with alignment of the transceiver, including transmitter driver stages and the MOSFET power
amplifiers.
Now might be a good time to check R-2. R-8, R-83, and R-91 to insure that they are turned
totally counter-clockwise. This is to make sure that the transmitter RF drive level is at
minimum, and that the MOSFET bias levels are also at minimum. During the alignment
procedure you will set these potentiometers at their proper levels.
To proceed with transceiver alignment you will need the following tools:
●50 ohm Dummy load. This can be an actual dummy load, or a bank of non-inductive resistors
which will withstand 12 watts or more for up to one minute.
●An Oscilloscope, or Diode Voltage Probe and Voltmeter for measuring RF voltage levels at 18
MHz.
●A DC Ampere Meter capable of measuring 0 to 300 ma, and 0 to 2 amperes. There is an
alternative way to measure the 0 to 300 ma levels using voltage across a resistor. This will be
discussed in the alignment procedures.
●The Microphone that you are going to use with this transceiver, or an audio signal generator and
suitable attenuators to adjust it's output to normal microphone signal levels (nominally 40 to 50
millivolts).
●A Frequency Counter, or other means to determine VFO frequency and tuning range. A
receiver with accurate frequency readout may be suitable.
Initial Alignment Procedure:
These steps will get you on the air. A more detailed alignment method is documented in the
troubleshooting section.
1. Set the BFO and carrier oscillator frequency:
Adjust the BFO (C-72) so that when you tune across a steady carrier you can hear the zero-beat
on each side of that carrier frequency. Then adjust C-72 to a slightly lower frequency where you
can hear the upper-sideband zero-beat tone but the lower-sideband one is either gone or very
much attenuated. Now tune in an on-air SSB signal and adjust C-72 very slightly for best audio
quality.
2. Set the carrier balance:
STEP-1: With an detector probe or oscilloscope monitorin the 12.96 MHz si nal at
Page 10 of 34
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