Hendricks QRP Kits BITX20A Assembly Manual

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Hendricks QRP Kits

BITX20A

Assembly Manual

27 October 2007

The BITX20 idea originated with a transceiver designed by Ashar Farhan VU3ICQ that was intended

to be easy to build from surplus and salvage components. That transceiver has been built and used by

many hams worldwide with great success. The BITX20A by Hendricks QRP Kits is a PCB realization

of the original design which includes a parts kit so you don't have to locate all the necessary

components. In addition, several upgrades have been added to make the transceiver output cleaner and

to raise power output to the full QRP limit of 10 watts.

There is a BITX20 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

This is how your new BITX20A kit will look as delivered.

Photo by KC0WOX

No, you don't get the pen or the wire stripper, just the box of parts.

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Do you have a question about the BITX20A and is the answer not in the manual?

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Summary of Contents for Hendricks QRP Kits BITX20A

Page 1 That transceiver has been built and used by many hams worldwide with great success. The BITX20A by Hendricks QRP Kits is a PCB realization of the original design which includes a parts kit so you don't have to locate all the necessary components.
Page 2 Opening the box you will see bags of parts and a PC Board. Photo by KC0WOX Photo by KC0WOX...
Page 3 Parts Inventory: Quantity Value Device Quantity Value Device 160 pf External tuning cap Resistors 10 uf POLARIZED CAP 100 uf POLARIZED CAP 220 pf POLYSTYRENE 470 pf POLYSTYRENE 30 pf Trim capacitor 0.01 uf 0.1 uf 150 K 10 pf 100 pf 2.2K 15 pf...
Page 4 Quantity Value Device Quantity Value Device 2N3904 Transistor SB320 Diode 2N5486 Transistor HEATSINK 2N7000 Transistor RELAY BS170 MOSFET FQN1N50C MOSFET LM386N-4 AF PA IRF510 MOSFET Quantity Value Device 3318_TRIMMER 1.2 uH molded choke 3318_TRIMMER 8.2 uH molded choke Fine tune external pot FT37-43 Toroid Core (Black) Volume control external T37-6...
Page 5 Photo by K7HKL It is advisable that you inventory your parts to make sure everything is available and ready for assembly. Each builder may have his/her own way of organizing parts, but if you do not, you might try using a block of Styrofoam packing material as shown in the above picture. Parts are sorted by type and size (ohms, micro-farads, etc).
Page 6 Some Assembly Recommendations: Before you start assembling your new BITX20A, there are a few things you might want to review. 1. Most of the resistors, diodes, and some axial leaded capacitors in this kit are installed on end. To make your kit look more professional, it is advisable to bend the longer lead of these components over a scrap of PCB material so that all your exposed lead bends look approximately the same.
Page 7 Kit Assembly Receive-Transmit Power Changeover Relay and Power Input Components [ ] D-17, 1N4004 Observe Polarity [ ] K1, 351 Relay Hold the relay body flat to the PCB while soldering. [ ] Connect push-to-talk part of microphone connector, or a temporary momentary switch as PTT. Note: Pads for the push to talk connection are provided along one edge of the board and are marked as PTT with the ground pad also marked with Gnd .
Page 8 Illustration 2: Receive Audio Pre-Amplifier (N7VE Photo) Illustration 3: Receive Audio LM-386 Power Amplifier (N7VE Photo) Receiver AF Amplifier [ ] C-36, 100 mfd Observe Polarity [ ] C-83, 0.1 mfd (marked 104 ) [ ] R-81, 10 ohms (brown-black-black) [ ] C-82, 10 mfd, Observe Polarity [ ] IC-1, LM386, Make sure you get this positioned properly when you insert it.
Page 9 [ ] R-80, 10K ohm potentiometer NOTE: Off-board component. Use 6 inch leads. Ground lead near C-82, Hot lead near Q-16. [ ] C-81, 10 mfd Observe Polarity [ ] C-80, 100 mfd Observe Polarity [ ] R-78, 4.7K ohms (yellow-violet-red) [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections...
Page 10 Illustration 4: Transmitter AF Amplifier (N7VE Photo) Transmitter AF Amplifier (Microphone Amplifier) [ ] R-76, 10 ohms (brown-black-black) [ ] R-92, 4.7K ohms (yellow-violet-red) NOTE: This is power for FET mike. Omit for dynamic or crystal mike. [ ] C-60, 10 mfd Observe Polarity [ ] C-76, 0.01 mfd (marked 104) [ ] R-73, 2.2K ohms (red-red-red) [ ] R-72, 10K ohms (brown-black-orange)
Page 11 [ ] R-74, 100 ohms (brown-black-brown) [ ] C-73, 100 mfd Observe Polarity [ ] R-93, 220 ohms (red-red-brown) [ ] C-77, 10 mfd Observe Polarity [ ] C-75, 100 mfd Observe Polarity [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections TEST: You can test the microphone amplifier by using an audio amplifier to monitor the negative side of C-77 while you key your microphone and talk into it.
Page 12 If you get these in the wrong places your receiver sensitivity and transmitter power output may be degraded. Swapping the 22 ohm resistor with one of the 220 ohm resistors is a common mistake in early BITX20 units and possibly in BITX20A kits. [ ] Solder [ ] Clip Excess Lead Length...
Page 13 BFO & Carrier Oscillator [ ] C-88, 33 pf NOTE: May not be needed, but provided to insure adequate tuning range. [ ] C-72, 30 pf variable capacitor, Note: flat side is RF side, round side is ground. [ ] L-5, 8.2 uh molded inductor (looks like a fat resistor with gray-red-gold-gold bands) [ ] X-5, 11.0 MHz Crystal.
Page 14 [ ] Inspect Solder Connections TEST: Insert an 11.0 MHz signal across R-64 and listen for a beat-note from the receive audio amplifier. Illustration 7: Second IF Amp Section (N7VE Photo) Receive 2nd IF Amp and Transmit 1st IF Amp [ ] C-64, 0.1 mfd (marked 104) [ ] R-58, 1K ohms (brown-black-red) [ ] R-57, 2.2K ohms (red-red-red)
Page 15 [ ] R-61, 220 ohms (red-red-brown) [ ] C-63, 0.1 mfd (marked 104) [ ] R-62, 100 ohms (brown-black-brown) [ ] R-56, 100 ohms (brown-black-brown) [ ] C-57, 0.1 mfd (marked 104) [ ] D-12, 1N4148 Observe Polarity [ ] Q-17, 2N3904 (Position according to layout stenciled on PCB) [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections...
Page 16 Illustration 8: Crystal Filter Section (N7VE Photo) Crystal Filter [ ] C-56, 82 pf (marked 82) [ ] C-55, 100 pf (marked 101) [ ] C-54, 82 pf (marked 82) [ ] X-1, 11.0 MHz [ ] Add ground wire soldered to crystal case [ ] X-2, 11.0 MHz [ ] Add ground wire soldered to crystal case [ ] X-3, 11.0 MHz [ ] Add ground wire soldered to crystal case [ ] X-4, 11.0 MHz [ ] Add ground wire soldered to crystal case...
Page 17 Illustration 9: Receiver First IF and Transmitter Second IF (N7VE Photo) Receiver 1st IF and Transmitter 2nd IF [ ] C-53, 100 pf (marked 101) [ ] R-46, 1K ohms (brown-black-red) [ ] R-45, 2.2K ohms (red-red-red) [ ] Q-10, 2N3904 (Position according to layour marked on PCB) [ ] R-48, 10 ohms (brown-black-black) [ ] C-44, 0.1 mfd (marked 104) [ ] Solder...
Page 18 [ ] Clip Excess Lead Length [ ] Inspect Solder Connections [ ] C-52, 100 pf (marked 101) [ ] D-10, 1N4148 Observe Polarity [ ] R-43, 220 ohms (red-red-brown) [ ] C-42, 0.1 mfd (marked 104) [ ] R-44, 100 ohms (brown-black-brown) [ ] Q-9, 2N3904 (Position according to layout marked on PCB) [ ] R-39, 2.2K ohms (red-red-red) [ ] C-43, 0.1 mfd (marked 104)
Page 19 Illustration 10: First Mixer (VFO Mixer), (N7VE Photo) 1st Mixer (VFO Mixer) [ ] T-4, 8:8:8 turns trifilar, 6 inches per #26 on FT37-43 (black) core. Twist to 8 twists per inch [ ] T-5, 8:8:8 turns trifilar, 6 inches per #26 of FT37-43 (black) core. Twist to 8 twists per inch [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections...
Page 20 [ ] C-30, 0.1 mfd (marked 104) [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections Illustration 11: VFO Section (N7VE Photo)
Page 21 [ ] R-35, 100 ohms (brown-black-brown) [ ] D-8, 1N4739A, 9.1 Volt Zener Observe Polarity [ ] R-33, 10K ohms (brown-black-orange) [ ] R-34, 10K ohms (brown-black-orange) [ ] C-33, 0.1 mfd (marked 104) [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections [ ] Q-8, 2N3904 (position according to layout marking on PCB) [ ] Q-7, 2N3904 (position according to layout marking on PCB)
Page 22 [ ] C-15, 180 pf (marked 180) [ ] C-37, 220 pf Polystyrene (marked 220) NOTE: Polystyrene caps are encased in clear plastic. [ ] C-39, 33 pf (marked 33) [ ] R-32, 4700 ohms (yellow-violet-red) [ ] C-91, 56 pf (marked 56) [ ] D-9, 1N4752A, 33 Volt Zener (used as fine tuning varicap) Observe Polarity [ ] Solder...
Page 23 NOTE: You can control your tuning range by selection of which capacitor sections you use: Polyvaricon Trimmer Open Trimmer Closed Section-A 60 kHz 58 kHz Section-B 124 kHz 120 kHz Sections A+B 155 kHz 147 kHz [ ] R-37, 10K Potentiometer. This is the fine tuning adjustment. [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections...
Page 24 [ ] R-20, 2.2K ohms (red-red-red) [ ] R-21, 1K ohms (brown-black-brown) [ ] R-23, 10 ohms (brown-black-black) [ ] R-22, 220 ohms (red-red-brown) [ ] C-26, 0.1 mfd (marked 104) [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections [ ] Q-5, 2N3904 (position according to layout stenciled on PCB) [ ] D-3, 1N4148 Observe Polarity...
Page 25 [ ] Q-4, 2N3904 (position according to layout marked on PCB) [ ] R-15, 1K ohms (brown-black-red) [ ] L-10, 1.2 uh molded inductor (brown-red-gold-gold) It looks like a fat resistor. [ ] C-25, 100 pf (marked 101) [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections Receive and Transmit Front End...
Page 26 [ ] C-14, 30 pf Install this capacitor according to outline stenciled on the PCB NOTE: The rounded side connects to ground and the flat side to RF [ ] C-13, 82 pf (marked 82) [ ] C-11, 10 pf (marked 10) [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections...
Page 27 [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections Antenna Filter [ ] C-47A, 100 pf (marked 101) [ ] C-47B, 100 pf (marked 101) [ ] L-2, 14 turns #26 (10 inches) on T-37-6 (yellow) core [ ] C-48A, 180 pf (marked 181) Illustration 16: Antenna Filter (N7VE Photo)
Page 28 change that provided additional harmonic reduction. [ ] C-49B, 100 pf (marked 101) [ ] C-49A, 100 pf (marked 101) [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections RF PA Drivers [ ] R-90, 100 ohms (brown-black-brown) [ ] C-9, 0.1 mfd (marked 104) [ ] Q-20, 2N5486 (position according to layout marked on PCB)
Page 29 [ ] Clip Excess Lead Length [ ] Inspect Solder Connections [ ] R-13, 22 ohms (red-red-black) [ ] C-6, 0.1 mfd (marked 104) [ ] T-3, 8:8 turns (6 inches each lead) bifilar on #26 on FT37-43, (black) core. Twist to 8 turns per inch [ ] R-5, 2.2K ohms (red-red-red) [ ] R-6, 2.2K ohms (red-red-red) [ ] C-4, 0.1 mfd (marked 104)
Page 30 Illustration: RF PA Stage RF PA Stage [ ] C-51, 0.1 mfd (marked 104) [ ] R-91, 10K potentiometer NOTE: Turn fully CCW [ ] R-2, 10K potentiometer NOTE: Turn fully CCW [ ] C-5, 0.1 mfd (marked 104) [ ] C-22, 0.1 mfd (marked 104) [ ] R-4, 2.2K ohms (red-red-red) [ ] R-1, 2.2K ohms (red-red-red) [ ] Solder...
Page 31 [ ] Solder [ ] Clip Excess Lead Length [ ] Inspect Solder Connections Congratulations. You have completed wiring your BITX20A kit, and are ready to proceed to the alignment section near the end of this document.
Page 32 Parts Placement Drawing: Drawing by KD1JV...
Page 33 Schematic Diagram: Schematic by N7VE...
Page 34 Alignment Method: BFO/Carrier Oscillator: There are several ways to adjust the BFO/Carrier Oscillator frequency. 1. Rough alignment may be made by adjusting C-72 while listening to a received SSB signal on 20 meters. This is a two-handed operation as you have to use the VFO Fine Tuning to keep the VFO frequency set for best intelligibility while searching for the best quality audio with C-72.
Page 35 Polyvaricon Capacitance Trimmer Open Trimmer Closed Section Range Tuning Range Tuning Range ========= ========= =========== ============ Section-A 4 to 80 pf* 60 Khz 58 KHz Section-B 5 to 160 pf* 124 Khz 120 KHz Sections A+B 9 to 240 pf* 155 Khz 147 KHz Illustration 21: *VFO Tuning Capacitor Parameters(K7HKL Photo)
Page 36 Receiver & Transmitter RF Filter: The easiest way to tune the RF input filter is to peak C-14 and C-18 in receive mode for loudest signal while listening to a relatively constant carrier from your antenna. This provides both receive and transmit mode alignment of this filter.
Page 37 RF compression becomes apparent. As you monitor the RF output and simultaneously increase the drive level, you should see the output rise fairly fast, with the rate of rise decreasing after you pass some point on the adjustment. This is the setting where RF compression starts. For best transmitted signal linearity you should set the drive level just below this start of compression point.