EA3GCY MFT-20 Assembly Manual Download Page 28 | Manualshive

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MFT-20 DSB Transceiver Kit

Page 28

SCHEMATIC

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Summary of Contents for MFT-20

Page 1: ...eiver 20 Meters DSB Transceiver Kit Assembly manual Last update June 1 2017 ea3gcy gmail com Most recent updates and news at www ea3gcy com Thanks for constructing the MFT 20 DSB Transceiver kit Have...

Page 2: ...io preamplifier and filter using an operational amplifier and an output amplifier for driving a loudspeaker The local oscillator is based on standard low cost quartz crystal of 14 328MHz with which it...

Page 3: ...omponent leads wire strippers long nose pliers needle nose pliers X Acto knife screwdriver for M3 screws alignment tool for adjusting IF transformers You will need a good light and a magnifying glass...

Page 4: ...There is a similar notch on one end of the IC socket that should be oriented over the U printed on the circuit board Finally pin 1 of the IC is also marked with a small dimple or dot this end of the I...

Page 5: ...K 502 502 or 53E trimmer 1 1K P1 RX Gain Potentiometer B 1K lin 1 50K P2 Tune Potentiometer B 50K lin Capacitor list Qty Value Checked Ref Identified 2 470n C39 C40 474 or 0 47 27 100n C1 C8 C9 C10 C1...

Page 6: ...d 1 T68 2 L4 Toroid Tuning inductor 17 mm diam red 4 1u2H 3335 L1 L2 L3 L6 shielded coils 1u2H 1u2H 2 FT37 43 L7 toroid 10t 3t L9 toroid 8t 8t 9 5 mm diam Black 1 14 328 X1 143 or 14 328 X2 not used 1...

Page 7: ...B Generator E 2 R16 56K green blue orange DSB Generator D 2 R17 56K green blue orange DSB Generator D 4 R18 10K brown black red Electret mic Bias F 1 R19 4K7 yellow violet red Electret mic Bias F 3 R2...

Page 8: ...P 82pK or 82J VFO out J K 5 C35 1n 102 or 0 001 VFO J 3 C36 82p 82P 82pK or 82J VFO out I 4 C37 100n 104 or 0 1 VFO K 2 3 C38 100n 104 or 0 1 VFO K 4 C39 470n 474 or 470K Mic Input D 1 C40 470n 474 or...

Page 9: ...4 5 IC8 78L08 MC78L08 TX Bias supply E 10 Inductors RF Transformers Checked Ref Value Type Ident Comment Circuit section Located L1 KANK3335 1u2H K3335 or 1u2H Rx Mix K 10 L2 KANK3335 1u2H K3335 or 1u...

Page 10: ...MFT 20 DSB Transceiver Kit Page 10 143 QUADRANT COMPONENT LAYOUT MAP...

Page 11: ...he Rx gain potentiometer and P2 is the TUNE potentiometer which will not be installed yet Refer to the parts list and select the first resistor R1 Bend the leads as close to the component body as poss...

Page 12: ...heir respective locations as identified on the circuit board in the same manner as you did with the resistors but leave a separation of 1 1 5mm from the board Diodes Next mount the diodes being carefu...

Page 13: ...stall and solder all the capacitors C1 to C67 except C27 and C57 they are not used When you mount them make sure to leave the leads as short as possible C63 C64 and C65 are polystyrene capacitors thes...

Page 14: ...tors have their type printed on the component body Place them according to the corresponding component outline printed on the circuit board Transistors Q1and Q2 of the type BC547 Q3 is a PN2222 Q4 is...

Page 15: ...riented towards the notch in the IC socket or the U on the component outline Mount the sockets for IC1 IC2 IC3 and IC6 in the locations printed on the circuit board Make sure that the sockets lie flat...

Page 16: ...ge soldering iron LPF Toroids L10 and L11 L10 and L11 are identical They use T37 2 cores red toroid with 9 5mm 0 375in OD Cut 20cm 7 5 of 0 5mm diameter enameled wire and wind eleven 11 turns on a red...

Page 17: ...nd the circumference of the toroid Leave pigtails of 10 20mm 0 70 Now take about 8cm 3 5 of 0 5mm diameter enameled wire and wind three 3 turns on the other side of the toroid spacing the turns within...

Page 18: ...o the direction of the winding Toroidal transformer L9 L9 is an impedance matching transformer with a bifilar winding An FT37 43 is used black toroid with 9 5mm 0 375in OD It has 8 8 turns Cut a 31 32...

Page 19: ...and separate the two windings Use a sharp X Acto knife to scrape the enamel off the ends that will be soldered The ends of the coils that we have made need to be prepared in this manner before solderi...

Page 20: ...nd in two stages Pass half of the wire through the toroid wind half of the toroid and then turn the toroid and wind the other half If you re not sure how many turns you have wound you can count them e...

Page 21: ...suppression and P1 RF gain volume potentiometer to mid position Connect a speaker or headphones to the SPEAK pins on the circuit board IMPORTANT Use a high quality speaker box A bad speaker will make...

Page 22: ...little bit of nail polish Another way to hold L4 may be using a little bit of hot melt adhesive or similar L4 should be well secured this is very important since vibrations may change the VXO frequenc...

Page 23: ...of DSB carrier suppression P4 Connect a power meter with a 50 ohm load to the antenna jack Adjust the mic gain to minimum completely clockwise Adjust P4 carrier suppression to mid position If you have...

Page 24: ...nging Install the antenna in the highest and clearest position possible Broadcasting Interference An inherent problem in direct conversion DC receivers is the broadcasting interference This occurs at...

Page 25: ...amateur radio and adapt the connections to the MFT or build your own micro The connection scheme is very simple Or you can build your own handheld microphone with the micro electret capsule included...

Page 26: ...hnical assistance is needed you are welcome to send an email to ea3gcy gmail com As a last resource you may send the kit in for repair however I will have to charge for any repairs done although I wil...

Page 27: ...ion and used correctly according to all provided instructions It is your responsibility to follow all the instructions in the manual to identify all the components correctly and to use good workmanshi...

Page 28: ...MFT 20 DSB Transceiver Kit Page 28 SCHEMATIC...

Page 29: ...TX RX full use RX TX Transceiver use normal use Note that if you use the RX along with the TX you do not have to connect anything in VFO TX V VRX VTX and RX ANT terminals The VFO TX and VTX terminals...

Page 30: ...MFT 20 DSB Transceiver Kit Page 30 WIRING To use RX only...

Page 31: ...or shielding screen tape The MFT 20 is not protected against reverse polarity It is a good idea is to place a diode i e BY255 or larger in parallel with the power supply input The cathode the end of t...

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