QRPKits BITX20A Conversion Instructions Download Page 26 | Manualshive

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Receive 2

nd

IF Amplifier

This section is a compound amplifier with Q11 providing voltage gain and Q17 providing current

gain. Overall amplification is controlled by feedback divider made up of R52 and R55.

Q11 voltages

Q17 voltages

(voltage measurements are made in receive mode)

Collector 4.61 VDC

Collector

9.77 VDC

Emitter 0.0 VDC

Emitter

3.88 VDC

Base 0.68 VDC

Base

4.60 VDC

Page 26 of 34

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Summary of Contents for BITX20A

Page 1: ...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...

Page 2: ...t 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 shiel...

Page 3: ...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 Cerami...

Page 4: ...Parts Placement Diagram Drawing by KD1JV Page 4 of 34...

Page 5: ...BITX17A Schematic Diagram Drawing by N7VE Page 5 of 34...

Page 6: ...TE 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 meas...

Page 7: ...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...

Page 8: ...move 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...

Page 9: ...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 R...

Page 10: ...e 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...

Page 11: ...lly adjust C 14 and C 18 for maximum received signal level There is some interaction between these 2 capacitors so you may need to re peak each capacitor adjustment several times to reach maximum sens...

Page 12: ...d Aaaaaaaaaaah into the microphone will also work if you do not have an audio signal generator Key the transmitter and slowly rotate R 83 to the right while watching the transmitter RF output An RMS v...

Page 13: ...Parts Placement Drawing Drawing by KD1JV Page 13 of 34...

Page 14: ...Schematic Diagram Schematic by N7VE Page 14 of 34...

Page 15: ...n key the transmitter Key the transmitter again and adjust the BFO Carrier Oscillator frequency C 72 for maximum signal level note the frequency on the counter and then adjust C 72 for a lower frequen...

Page 16: ...citor will provide some adjustment but you will need to select which capacitor sections are connected to set the minimum maximum tuning limits and the tuning range Polyvaricon Capacitance Trimmer Open...

Page 17: ...ed in adjusting the transmitter drivers section but you do have to set the bias adjustment Drive level adjustment will be done in the RF PA alignment section 1 Connect a 2 to 3 ampere DC ammeter in se...

Page 18: ...ld set the RF output level no higher than the point where RF compression becomes apparent As you monitor the RF output and simultaneously increase the drive level you should see the output rise fairly...

Page 19: ...The following voltage measurements are made in receive mode LM386 Voltages Q 16Voltages Q 25 Voltages Pin 1 1 34 VDC Collector 10 97 VDC Collector 5 94 VDC Pin 2 0 0 VDC Emitter 5 26 VDC Emitter 0 0...

Page 20: ...common in inexpensive audio devices tape recorders etc or can be purchased directly from component suppliers Most inexpensive computer microphones are Electret types Audio input level for transmitter...

Page 21: ...VXO adjustment allows you to set the crystal oscillator to it s proper frequency which is 12 to 20 db down the lower sideband skirt of the crystal filter Because the oscillating waveform will affect...

Page 22: ...minimum output There should be two points on C 65 where the R 64 voltage is at minimum this verifies that you are not at the end of the adjustment range The dip in voltage across R 64 should occur at...

Page 23: ...ly across the IF passband note and record R 64 signal levels at every 200 Hz frequency step For a rather crude looking chart you can simply plot the voltage readings on graph paper to determine your f...

Page 24: ...bandwidth The value of C 55 should equal approximately twice the value of C 54 or C 56 but there is some room to experiment to see how changes affect the ripple factor across the passband and steepne...

Page 25: ...Receive 1st IF Amplifier Q 9 Voltages voltage measurements are made in receive mode Collector 7 62 VDC Emitter 1 62 VDC Base 2 35 VDC Page 25 of 34...

Page 26: ...d Q 17 providing current gain Overall amplification is controlled by feedback divider made up of R 52 and R 55 Q 11 voltages Q 17 voltages voltage measurements are made in receive mode Collector 4 61...

Page 27: ...Transmit 1st IF Amplifier Q 12 Voltages measured in transmit mode Collector 8 57 VDC Emitter 1 93 VDC Base 2 65 VDC Page 27 of 34...

Page 28: ...Transmit 2nd IF Amplifier Q 10 Voltages measured in transmit mode Collector 7 59 VDC Emitter 1 63 VDC Base 2 35 VDC Page 28 of 34...

Page 29: ...alignment steps are 1 Set the Fine Tune potentiometer to mid point 2 Open C 38 the polyvaricon to minimum capacitance 3 Adjust C 38 trimmer capacitor so the VFO is operating at or just above 5 208 MHz...

Page 30: ...Receive RF Amplifier Q 5 Voltages measured in receive mode Collector 7 62 VDC Emitter 1 65 VDC Base 2 36 VDC Page 30 of 34...

Page 31: ...68 and L 10 form a series resonant bandpass filter to block VFO and IF energy from reaching the transmit amplifier stages Q 4 Voltages measure in transmit mode Collector 7 60 VDC Emitter 1 61 VDC Base...

Page 32: ...and L 4 will not tune to midpoint in the 17 meter band adjustment should be made by adding or subtracting turns on L4 If C 20 C 18 and L 6 will not tune to midpoint in the 17 meter band adjustment sho...

Page 33: ...ing transmit and shunts RF to ground during that period Q 26 2N7000 is in OFF mode during transmit and blocks RF during transmit Q 24 2N7000 is in ON mode during transmit and shunts RF to ground durin...

Page 34: ...VDC Emitter 2 52 VDC Base 3 27 VDC Q 18 BS170 Q 19 BS170 Drain 11 46 VDC Drain 11 46 VDC Source 0 044 VDC Source 0 044 VDC Gate adjust VDC Gate adjust VDC 20 ma 0 044 volts DC Q 1 IRF510 Q 2 IRF510 D...

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