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Hendricks QRP Kits BITX20A, Assembly Manual

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Hendricks QRP Kits BITX20A Assembly Manual Download Page 19

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

[ ] D-4, 1N4148 Observe Polarity

[ ] D-5, 1N4148 Observe Polarity

[ ] D-6, 1N4148 Observe Polarity

[ ] D-7, 1N4148 Observe Polarity

[ ] R-26, 100 ohms  (brown-black-brown)

Illustration 10: First Mixer (VFO Mixer), (N7VE Photo)

Summary of Contents for BITX20A

Page 1: ...arts 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 ...

Page 2: ...Opening the box you will see bags of parts and a PC Board Photo by KC0WOX Photo by KC0WOX ...

Page 3: ...POLYSTYRENE 2 22 2 470 pf POLYSTYRENE 13 100 4 30 pf Trim capacitor 14 220 2 470 1 0 01 uf 3 10K 40 0 1 uf 2 150 K 3 10 pf 15 1K 10 100 pf 11 2 2K 1 15 pf 1 2 7K 3 180 pf 1 22K 2 220 pf 1 3 3K 3 33 pf 11 4 7K 1 0 022 uf 5 11 MHz XTAL S 2 56 pf Quantity Value Device 1 8 2 pf 1 33v ZENER_DO35_V 4 82 pf 1 5 6v ZENER_DO35_V 1 9 1v ZENER_DO35_V 1 1N4004 Diode 12 1N4148 Diode ...

Page 4: ...4 2N7000 Transistor 1 RELAY 2 BS170 MOSFET 1 FQN1N50C MOSFET 1 LM386N 4 AF PA 2 IRF510 MOSFET Quantity Value Device 2 200 3318_TRIMMER 1 1 2 uH molded choke 3 10K 3318_TRIMMER 1 8 2 uH molded choke 1 10k Fine tune external pot 8 FT37 43 Toroid Core Black 1 10K Volume control external 5 T37 6 Toroids Core Yellow ...

Page 5: ... 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 Toroid cores in this picture are stacked on wooden toothpicks which were inserted into the Styrofoam ...

Page 6: ...aterial so that all your exposed lead bends look approximately the same 2 You will be twisting enamel coated wires together to make the windings for toroid transformers To do this you can use the drill and bent nail method or fabricate a manual twisting device from stiff wire and a tubular insulator 3 Be especially observant of component orientation stenciled on the PCB Polarized components must b...

Page 7: ...esting purposes during alignment Caution The changeover relay applies ground to the receive section power feeds during transmit mode and ground to transmit power feeds during receive mode This means that you cannot jumper 12 volts to the transmit sections while in receive mode and cannot jumper 12 volts to the receive sections when in transmit mode without shorting something and possibly damaging ...

Page 8: ... IC 1 LM386 Make sure you get this positioned properly when you insert it Solder Clip Excess Lead Length Inspect Solder Connections C86 100 mfd Observe Polarity R 82 10 ohms brown black black R 79 220 ohms red red brown Illustration 2 Receive Audio Pre Amplifier N7VE Photo Illustration 3 Receive Audio LM 386 Power Amplifier N7VE Photo ...

Page 9: ...red R 89 22K ohms red red orange C 47 0 pf This is an artifact from an older PCB design Do not install any capacitor here C 79 0 022 mfd marked 22K R 77 3 3K ohms orange orange red C 8 10 mfd Observe Polarity Speaker or Headphone Jack Connection Use 6 inch leads Ground is the pad near C 75 Solder Clip Excess Lead Length Inspect Solder Connections TEST At this point you can test your receiver audio...

Page 10: ...ike 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 R 75 1K ohms brown black red Solder Clip Excess Lead Length Inspect Solder Connections Q 15 2N3904 position matching that stenciled on PCB Illustration 4 Transmitter AF Amplifier N7VE Photo ...

Page 11: ...older 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 BFO Mixer Assembly T 6 8 8 8 turns 28 trifilar on FT37 43 black core This is three wires each 6 inches long Twist them together for 8 twists per inch and wind this on the core Illustration 5 BFO Mixer Section N7VE Photo ...

Page 12: ... 63 22 ohms red red black R 64 220 ohms red red brown NOTE Pay particular attention to the location and values of R 63 R 64 and R 65 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 L...

Page 13: ...d 221 R 70 150K ohms marked brown green yellow Solder Clip Excess Lead Length Inspect Solder Connections Q 14 2N3904 Position according to layout stenciled on PCB R 71 1K ohms brown black red C 70 100 mfd Observe Polarity R 69 100 ohms brown black brown R 68 1K ohms brown black brown Q 13 2N3904 Position according to layout stenciled on PCB Solder Clip Excess Lead Length Inspect Solder Connections...

Page 14: ... Amp C 64 0 1 mfd marked 104 R 58 1K ohms brown black red R 57 2 2K ohms red red red Q 12 2N3904 Position according to marking stenciled on PCB R 60 4 7 ohms yellow violet black C 61 0 1 mfd marked 104 R 59 470 ohms yellow violet brown Solder Clip Excess Lead Length Inspect Solder Connections D 13 1N4148 Observe Polarity Illustration 7 Second IF Amp Section N7VE Photo ...

Page 15: ...0 ohms yellow violet brown R 55 4 7K ohms yellow violet red R 52 1K ohms brown black red Q 11 2N3904 Position according to markings stenciled on PCB Solder Clip Excess Lead Length Inspect Solder Connections R 54 4 7K ohms yellow violet red C 59 0 1 mfd marked 104 R 51 220 ohms red red brown C 89 100 pf marked 101 C 62 100 pf marked 101 Solder Clip Excess Lead Length Inspect Solder Connections TEST...

Page 16: ... 0 MHz Add ground wire soldered to crystal case X 4 11 0 MHz Add ground wire soldered to crystal case Solder Clip Excess Lead Length Inspect Solder Connections TEST Insert an 11 0 MHz signal at pin 1 of X 11 and listen for a beat note from the receive audio amplifier You may have to tune around a bit to get the signal within the filter passband Illustration 8 Crystal Filter Section N7VE Photo ...

Page 17: ...ed on PCB R 48 10 ohms brown black black C 44 0 1 mfd marked 104 Solder Clip Excess Lead Length Inspect Solder Connections R 47 220 ohms red red brown D 11 1N4148 Observe Polarity R 49 220 ohms red red brown C 45 0 1 mfd marked 104 C 46 0 1 mfd marked 104 R 50 100 ohms brown black brown Solder Illustration 9 Receiver First IF and Transmitter Second IF N7VE Photo ...

Page 18: ...2N3904 Position according to layout marked on PCB R 39 2 2K ohms red red red C 43 0 1 mfd marked 104 R 40 1K ohms brown black red R 41 220 ohms red red brown R 42 10 ohms brown black black C 40 0 1 mfd marked 104 Solder Clip Excess Lead Length Inspect Solder Connections TEST Insert an 11 0 MHz signal at the junction of C 43 and C 45 and listen for a beat note from the receive audio amplifier ...

Page 19: ...s trifilar 6 inches per 26 of FT37 43 black core Twist to 8 twists per inch Solder Clip Excess Lead Length Inspect Solder Connections D 4 1N4148 Observe Polarity D 5 1N4148 Observe Polarity D 6 1N4148 Observe Polarity D 7 1N4148 Observe Polarity R 26 100 ohms brown black brown Illustration 10 First Mixer VFO Mixer N7VE Photo ...

Page 20: ... C 30 0 1 mfd marked 104 Solder Clip Excess Lead Length Inspect Solder Connections VFO Illustration 11 VFO Section N7VE Photo ...

Page 21: ...ing to layout marking on PCB Solder Clip Excess Lead Length Inspect Solder Connections R 31 1K ohms brown black red C 32 0 1 mfd marked 104 R 28 1K ohms brown black red R 27 1K ohms brown black red R 30 10 ohms brown black black R 29 100 ohms brown black brown C 31 0 1 mfd marked 104 Solder Clip Excess Lead Length Inspect Solder Connections R 36 2 2K ohms red red red C 90 33 pf marked 33 C 35 470 ...

Page 22: ...til you are sure that you have the desired tuning range You may have to add or delete a turn if you want something other than the standard tuning range Once you are sure you have the proper tuning range you can secure the VFO inductor by cutting a small scrap of hot melt glue placing that inside the toroid and melting it with the tip of your soldering iron Be sure to wipe the iron tip soon afterwa...

Page 23: ...s A B 155 kHz 147 kHz R 37 10K Potentiometer This is the fine tuning adjustment Solder Clip Excess Lead Length Inspect Solder Connections TEST Monitor the VFO frequency on a counter or with a receiver that is capable of tuning 3 0 to 3 5 MHz Receive and Transmit RF Amplifiers C 27 0 1 mfd marked 104 C 29 0 1 mfd marked 104 Illustration 12 Receive and Transmit RF Amplifiers N7VE Photo ...

Page 24: ... PCB D 3 1N4148 Observe Polarity R 24 220 ohms red red brown R 25 100 ohms brown black brown C 28 0 1 mfd marked 104 Solder Clip Excess Lead Length Inspect Solder Connections D 2 1N4148 Observe Polarity R 18 220 ohms red red brown C 23 0 1 mfd marked 104 R 19 100 ohms brown black brown R 16 220 ohms red red brown R 17 10 ohms brown black black C 21 0 1 mfd marked 104 Solder Clip Excess Lead Length...

Page 25: ... 2 L 6 18 turns 20 inches 26 on T 37 6 yellow core C 18 30 pf Observe Polarity NOTE The rounded side connects to ground and the flat side to RF C 20 82 pf marked 82 Solder Clip Excess Lead Length Inspect Solder Connections C 19 10 pf marked 10 C 17 56 pf marked 56 C 16 10 pf marked 10 L 4 18 turns 20 inches 26 on T 37 6 yellow core Solder Clip Excess Lead Length Inspect Solder Connections Illustra...

Page 26: ...fter wiring is completed T R Switches Q 23 2N7000 position according to layout marked on PCB R 86 4 7K ohms yellow violet red R 87 4 7K ohms yellow violet red Q 24 2N7000 position according to layout marked on PCB Q 26 2N7000 position according to layout marked on PCB R 94 4 7K ohms yellow violet red C 41 0 1 mfd marked 104 Solder Clip Excess Lead Length Inspect Solder Connections R 85 4 7K ohms y...

Page 27: ... Excess Lead Length Inspect Solder Connections L 1 12 turns 8 inches 26 on T37 6 yellow core NOTE L1 is 14 turns for kits 1 through 100 and 12 turns for kits above number 100 C 92 68 pf NOTE C 92 is not provided on kits 1 through 100 and is provided in kits above number 100 The provision of C 92 and reducing L1 from 14 to 12 turns is a late Illustration 16 Antenna Filter N7VE Photo Illustration 17...

Page 28: ... to layout marked on PCB R 83 200 ohm variable NOTE Turn fully CCW Counter Clock Wise C 10 0 1 mfd marked 104 Solder Clip Excess Lead Length Inspect Solder Connections R 9 2 2K ohms red red red R 10 1K ohms brown black red Q 3 2N3904 position according to layout marked on PCB R 12 10 ohms brown black black C 12 0 1 mfd marked 104 R 11 100 ohms brown black brown Solder Illustration 18 RF PA Drivers...

Page 29: ...rked 104 R 8 10K potentiometer NOTE Turn fully CCW Solder Clip Excess Lead Length Inspect Solder Connections Q 18 BS170 position according to layout marked on PCB Q 19 BS170 position according to layout marked on PCB R 7 2 2 ohms red red gold C 7 0 1 mfd marked 104 T 2 8 8 8 turns 6 inches each lead trifilar 26 on FT37 43 black core Twist to 8 turns per inch Solder Clip Excess Lead Length Inspect ...

Page 30: ...y 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 Clip Excess Lead Length Inspect Solder Connections C 1 0 1 mfd marked 104 C 2 0 1 mfd marked 104 Illustration RF PA Stage ...

Page 31: ...re is no requirement to fasten them to the PCB Soldering the attached MOSFETs to the PCB will be adequate for holding the heat sinks in place Q 2 IRF510 Bolt Q 2 to heat sink then install MOSFET and heat sink as a unit The heat sink legs are inserted in PCB holes provided for them There is no requirement to fasten them to the PCB Soldering the attached MOSFETs to the PCB will be adequate for holdi...

Page 32: ...Parts Placement Drawing Drawing by KD1JV ...

Page 33: ...Schematic Diagram Schematic by N7VE ...

Page 34: ...cy and a 24 to 40 db decrease in monitored signal level Un key the transmitter The BFO Carrier Oscillator frequency needs to be just outside the lower frequency edge of the crystal filter for USB operation Disconnect the frequency counter key the transmitter and re check to see that you are still at the same signal attenuation point on your scope or voltmeter Un key the transmitter This checks to ...

Page 35: ...pf 124 Khz 120 KHz Sections A B 9 to 240 pf 155 Khz 147 KHz Since the IF frequency is 11 0 MHz the VFO needs to tune 11 MHz below your desired tuning range on 20 meters 14 000 11 0 3 0 MHz You can use this method to calculate the frequency of the VFO for your particular tuning selection Illustration 21 VFO Tuning Capacitor Parameters K7HKL Photo ...

Page 36: ...20 ma of current would equal a voltage drop of 0 02 X 2 2 0 044 volts RF PA There are no tuning adjustments in the RF PA section but you do have to adjust the idling current on the two IRF510 MOSFET devices and then set the drive level for best output linearity To do this you will need an ammeter with a capability of reading 2 5 or 3 amperes PA Idling Current Adjustment 1 Connect an ammeter in ser...

Page 37: ...method of saying a long Aaaaaaaaaaaaaah while monitoring the RF output with a scope diode detector and voltmeter or watt meter 2 Key your transmitter and insert the tone while monitoring the RF output and slowly adjusting the RF drive pot R 83 for an increase in output Identify the adjustment position where rate of output increase seems to slow Back the drive level back down by watt or so This is ...

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