: Hacking Bitx Version3B, C: : 20mt to 40mt band: PART I Fig 1: Bitx Ver3C SBL-1 20 Conversion for Bitx40 The picture in Fig1 is a Bitx3C SBL-1 for 40mt band, constructed from the Bitx Version 3C SBL-1 20mt Exciter and PA Boards. The Bitx 40 can be built with our existing boards Bitx3B, Bitx3C SBL-1 and Bitx3C ADE-1 20mt boards, with this hack and also with the new 40mt boards and kits. The new 40mt boards have been modified for all our versions. There is not much difference between our various boards as far as the circuit is concerned with; the Bitx3B uses the conventional diode mixers where as the Bitx3C SBL uses the SBL-1 mixers and the other Bitx3C uses the ADE-1 mixers from mini circuits. The Bitx3B manual covers each stage in detail and can be used for reference when building any of these boards for 40mt or 20mt bands, only keeping in mind the required frequencies for VFO, BFO etc. The Bitx Version 3B 3C 20mt can be hacked very easily for 40mt band with some minor changes, so with a very few minor changes our 20mt board can work for 40mt also, in case you bought a kit for 20mt and would like to use it for 40mt band, or would like to modify your existing 20mt tcvr for 40mt band. We are not writing complete manual, just short notes on the changes done. The new exciter and pa boards for all versions for 40mt have these changes done. Subsequently we shall further add notes to the Bitx20 and Bitx40 versions.
The DC Voltages are same since we have not changed any components or circuitry the RF voltage may not be same in the PA if you are going to compare with the reading given on the Bitx3B 20mt manual, for peak power output from PA Bitx40. The RF Power output of Bitx3C SBL-20mt is around 6 watts and the RF power output of Bitx40 is around 13 watts, when the power supply is between 24Volts DC to 28Volts DC. Changes in Exciter for converting Bitx3B, 3C- 20Mt To Bitx3B, 3C to 40Mt band BFO: A jumper has to be put across L5 as shown in Fig.2 below. This is required to replace the 10uh coil, which was used for USB; we do not require that, since we are to use LSB for 40mt band. The trimmer if needed and an extra capacitor pad are already in place for the crystal to make it resonate on LSB mode, with a suitable value capacitor if required only, as the 22pf trimmer may alone be sufficient, as in our prototype BFO. The BFO freq should be 1.5 khz above the IF Filter frequency for LSB mode. The new exciter board for 40mt has this change done. Fig 2: Bitx Version 3C SBL-1 Modification BFO. Put a jumper across L5 for LSB mode for 40mt band. VFO: We are required to change the toroid core to wind wire on L4 from T37-6 to T50-2. The coil would require 60 turns to wind with SWG #34 gauge copper wire. No change has been made in any other components.
The VFO tunes from 2.776.51 MHZ to 3064.85 MHZ, thus, giving complete coverage on 40mt band, when used with Isv149 and 5k-multi turn pot. The frequency when mixed with 10MHZ IF would produce freq as below in Fig 3 and 4. Fig 3: Counter Display Freq. From 6.99.98 MHZ Fig 4: To 7.217.83 MHZ Mounting position for ISV149 The ISV149 varactor diode has to be mounted in the correct position, or else The VFO would not cover the complete band, as in Fig 5. Fig 5: Bitx Version 3C SBL-1 mounting position of ISV149 varactor diode
Fig 6: 5k Multi turns Pot Connections. The 5K multi-turn pot has to be wired as given in Fig.6 If the wiring connections Are not as per the picture then the VFO coverage would be only 50KHZ. Fig 7: Bitx Version 3C SBL-1 Polystyrene caps marked in red boxes. For the VFO to remain stable we need to make use of Polystyrene capacitors as shown in Fig7. Polystyrene capacitors are marked in red boxes.
Using DDS with Bitx A suitable DDS can be used in place of the VFO. The input for DDS is taken From the base of Q7 VFO stage, which works as an amplifier here, thus boosting the output of the DDS. Suitable measurements have to be made to see if the DDS already has an inbuilt amplifier stage; in this case Q7 stage would have to be omitted, as the amplification may already have been done. The Q7 stage would have to be built for using the DDS, if DDS output is low. The 8V regulator has to be removed and also Q5 and Q6, which will not be required with the DDS. The components around Q7 that have to be mounted on the board are marked in Red boxes as showed in Fig 8. Fig 8: Bitx Version 3C SBL-1 DDS input base of Q7 Crystal Filter: The same IF crystal filter 10MHZ is being used for our Bitx 40mt hack.the IF frequency can be changed according to one s preference, as well as the VFO frequency, as in Fig 9. Fig 9: IF Crystal Filter 10 MHZ
Band Pass Filter: For Band Pass Filter coils L1 L2 L3 we are using the same coils as used in Bitx20mt. These coils tune between 2.5uh to 4uh. These coils work okay for 40mt also. We would need to tune the coils with 127 PF. We have used 100PF and 27 PF in parallel to get the correct value. As in Fig.10 and 11. The tuned capacitor pads were meant for a single component. i.e. 39pf for 20mt, we would need to use 127pf for 40mt band, this can be done by using 100Pf on the pad and soldering 27pf on the solder side of the pad as in Fig10. for the Bitx20 boards to tune the coils for 40mt band. How ever the new 40mt boards for all the versions have already been placed with extra pads for 100PF and 27PF. Fig 10: Bitx 20 MT Exciter Board BPF Converted for 40mt band. 27 PF x 3 on top side Of board. Fig 11: Bitx 20 MT Exciter Board BPF Converted for 40 mt band 100PF x 3 solder side Of board.
BITX VERSION 3 B-3C 40mt Exciter Coils: 1. T1 a,b - 8 Turns # SWG 34 Triflilar Enameled Wire on T37-43 used in older Bitx Version3, Bitx Version 3B 20mt and 40mt, Fig 12,13.For Bitx Version 3C 40mt and 20mt bands, SBL-1 or ADE-1 mixers are used. Fig 12: T1 T1A T1B 2 Nos Fig 13: T2 2. T2-8Turns # 34 Trifilar Enameled wire on T37-43 used in Bitx3B 20mt. Same for our Bitx40mt 3B as in Fig 13: SBL-1 mixers are used in Bitx3C And ADE- 1mixers in another Bitx3C version for both 20mt and 40mt,as in Fig 14,15. Fig 14: SBL-1 Mixers For T1And T2 IN Bitx 3C Fig 15: Mini Circuits ADE-1 Mixers Bitx3C will make use of SBL-1 Or ADE-1 instead of T1 and T2 as per board and T1 And T2 want be required for BitxC versions, but T1 and T2 Will be required for the Bitx3B 40mt and 20mt band s which uses the diode mixers. 3. T3. 8 Turns SWG # 34 Bifilar Enameled wire on T37-43 as used in Bitx3B 3C 20mt, 40mt same as in Fig 15. Fig 15: T3
4. L4-60 Turns # 34 on T50-2 Core. Used in Bitx3B and 3C-40mt boards. As in Fig 16: Fig: 16: L4 5. L1 L2 L3 10MHZ IF Coil tuned with 127Pf. same coil as used in Bitx20mt and Bitx 40mt for all boards as in Fig 17. Fig 17: L1L2L3 Power Amplifier: Fig 18: Bitx Version 3 PA Board 20mt, modified to 40mt The driver and the power amplifier stages for the 40mt band are same as in Bitx20mt.
No changes in any components have been made except for the change of Toroid cores in Driver, PA, Low Pass Filter and RFC have been made; the toroid cores and the number of windings have been changed for 7 MHz. The 40mt and 20mt boards silk screen has a single change, only the low pass filter capacitor values have been changed on the silk screen, otherwise the boards are exactly the same. A bigger heat sink would be required for the IRF 510 as in Fig 18. BITX VERSION 3 B-3C 40mt PA Coils: 1. T1-16 Turns #26 SWG Bifilar Enameled wire on FT50-43 core. Fig19. Fig 19: T1 2. T2 2 Turns #26 SWG Bifilar Enameled wire on FT50-43 core. 4uh Fig 20, 21 Fig 20: T2 Fig 21: T2 3. L1 - As many turns as possible #26 on FT50-43 core. Single-layer. Fig 22. Fig 22:L1 4. L2-0.55uh 14 Turns # 26 SWG on T37-6 core. Single layer. Fig 23. Fig 23: L2
5. L3-0.49uh 10 Turns #26 SWG on T50-2 core. Single layer. Fig 24. 6. L4-0.49uh 10 Turns #26 SWG on T50-2 core. Single layer. Fig 24. Fig 24: L3 L4 Low Pass Filter: For low pass filter to work on 40mt band L3 L4 need to be changed from T37-6 To T50-2, and also by changing the capacitor value across the coils, As per picture below, 220PF, 1500PF, 220PF, 100 volts. Silver Mica or Disc Capacitors can be used. L3, L4 coils are wound 10 turns on T50-2 with SWG # 26 SWG copper wire. As in Fig 25 Fig 25: Bitx Version 3C/B 40mt PA Board. Low Pass Filter Section.
Notes: In some of our built Bitx version 3 series for 20mt and 40mt we have omitted the 100uh and.001, if you feel the TX audio is better with removing them then just place a jumper in place of 100uh and remove the 0.001 capacitor as in Fig26. The circuit is already using 0.001 across microphone for filtration, so this stage can be bypassed with as in Fig 26. Fig 26: Bitx Version 3C 3B exciter board, mod in TX modulation The 50 0hms impedance matching filter used ahead of the IRF 510 with L2 100PF And 220PF can also be done away with using a 10 ohms resistor in place of T2 and removing 100PF and 220PF, but do not remove 220PF from drain of IRF 510 to ground or else the PA would oscillate. The PA bias is same and kept at 50ma; the IRF 510 can be operated from 18V to 28V and would give RF final output as per the final voltage applied. Our Bitx40mt 3C SBL as in picture is giving an RF output of 13 Watts as measured on a Diamond wattmeter with 50 ohms dummy load.
Fan Connection: The +12V volts supply if taken from the TX point works better, as this way noise generated by Fan is not picked up, but if the supply is taken from RX side, then a disturbing sound is heard in the audio. For this you would have to take a connection from one end of the 68 Ohms 1 watts resistor with a short piece of wire and solder on the TX +12V connection on the pad as below in Fig 27, 28, 29 Fig27: Fan connection through 68 ohms 1 watt Fig28: Fan connection through 68 ohms 1 watt Fig29: Fan-connection on TX pad.
Picture Album Bitx3C 40mt T50-2 X 1 TUNABLE COIL: 2.5uh To 4uh Fig 30: L4 VFO COIL Fig 31: L1 L2 L3 BAND PASS FILTER COILS Fig 32: SBL-1 Mixers Mini Circuits Fig 33: ADE-1 Mixers Mini Circuits FT50-43 x 1 T50-2 X 2 Fig 34: L1 RFC PA Fig 35: L3 L4 LOW PASS FILTERS
T37-6 x 1 FT50-43 x 1 Fig 36: L2 IRF 510 Filter Fig 37: T1 PA DRIVER COIL FT50-43 x 1 Fig 38: T2 FINAL PA COIL 4uh
Fig 39: BITX VERSION 3B 40MT EXCITER BOARD Fig 40: BITX VERSION 3 SBL-1 40MT EXCITER BOARD
IN RX SWITCHING STAGE IN4148 TO BE CHANGED TO IN4007 Fig 41: BITX VERSION 3B 3C PA BAORD 40MT Fig 42: BITX VERSION 3C SBL-1 40MT VFO
Fig 43: BITX VERSION 3C SBL-1 40MT EXCITER Fig 44: BITX VERSION 3C SBL-1 40MT LOW PASS FILTER
Fig 45: BITX VERSION3B- 3C SBL-1 40MT PA Fig 46: BITX VERSION 3B 3C SBL-1 40MT AUDIO MUTE SECTION
Fig 47: BITX VERSION 3C SBL-1 40MT CASE PANEL Fig 48: BITX VERSION 3C SBL-1 TCVR CASE : COLOR SIEMENS GREY
Fig 49: BITX VERSION 3C SBL-1 SSB QRP TCVR 6 WATTS The article hacking Bitx Version 3B 3C has been written after successfully trying out the modification for using Bitx3C SBL-1 on 40mt band. Further improvements can be made by the builders. Disclaimer: The RX and TX are working satisfactorily. The building or modification with your existing Bitx version 3 series boards can be tried by taking your own decision, and we do not take any responsibility for the same. To Whom It May Concern: The Bitx Version 3 series SSB transceivers are adapted and modified from the design of Bitx20, original author of Bitx Mr. Ashar Farhan by due consent. A few pictures have been taken from the Bitx3 Manual by Om Leonard Kits and printed circuits boards for all our Bitx Version 3 series including the new 40mt boards and kits can be purchased from our ebay store. Fusion Radio VU3SUA. Or from our website: http://amateurradiokits.in Kindly report us of any errors. Sunil Lakhani VU3SUA Dated 20 July 2016 PART II: Schematics for Bitx3B 3C Exciter and PA for 40mt