MKARS80 construction manual V1.2 - Radio-Kits
Contents
1. MKARS 80 construction manual Bge Released 5 10 08 V1 2 PCB overlay a a PA 8 a le Oh l Ek lt R ee a 1 ju S P CONL CON2 Internal O Top silk it C7 c8 et loudspeaker Lei eo Ces 6 f ei Gen 2 C14 SI cu 8 Mee z ke p gt ce uE C12 oat ER ert geg ef ao 8 es S SCH2. R22 LS R43 R54 R5 C45 eee ol InF Mylar Marked 2A 102J Be careful not to mix the 4K7 and 47K resistors these two values are c59 ceo often confused The orientation of trimmer capacitors is marked by the PCB legend 4k7 Resistor Yellow Violet Red Gold its best to fit as directed so that the adjustment screw is at ground biz R20 R49 RM potential 10k Resistor Brown Black Orange Gold 5 5 30pF Open trimmer Non enclosed trimmer capacitor ba Ru LIRE RB RAO CO S R56 II Zener diodes are polarised that is they can only be fitted one way 47k Resistor Yellow Violet Orange Gold round there is a band on one end of the glass envelope which should pi Ra R42 rR o match up with the band marked on the overlay 100k Resistor Brown Black Yellow Gold 2V7 400mW Zener diode Ra a e Fe 180k Resistor Brown Grey Yellow Gold All the following components are taken from bag 2 R27 R30 R31 R35 R76 Semer pF Ceramic The following resistors are metal film close tolerance types with the ee ee eo value marked as 5 coloured bands 22pF Ceramic 22 12k 1 Resistor Brown Red Black Red Brown ee WE R20 68pF NPO Ceramic 68 33k 1 Resistor Orange Orange Black Red Brown re Ee Re MKARS 80 construction manual e Released 5 10 08 V1 2 100pF Ceramic 101 Axial inductors have a similar appearance to resistors but large
3. Z e LE 16V SZ AZ e M 3 EI c39 Ze 3 e SE g e R35 A z es 180k Z x 100n N7 R7 d SSASSN 220R cin c67 oS eS ee ca TP LOMHz Cut link when L e m CT izcr 16v 1009F ce pe gt pee o igor R26 Battery Gnd Banery ue waing pauar T Gemeng es SE Baus a 10k R17 13 CN L Re Mke gt TuF 16V TX 12V R27 10R 180k Fl S7 ad Bes V DN o d UD g G D m ag e zs D D mg o R40 4 BC547 SE ECE SE SE SE SS SE S 18k c4a 4 e Q3 TP VFO N um BC337 VM lc ea Ka 1000F Ict Mike e SZ D3 in LM386N 1 ETT R13 cA 1N5401 Si 1ouF jeu LI ee E 4 ZI V7 S7 cio o7 CS Ces Ic2 K BCSA7 a SE d S RI2 PIC16F818 1 P D J 47k e 16v K Vv D ESCH V Rit R3 V V V V jja 10k fk D D x 7 DC Power Microphone Loudspeaker Headphones CON4 CONI CON2 SZ
4. Die D17 dis Ing D20 WD D9 Dio TI Fit 18 pin socket to IC2 position with notch to match indication on IN5401 Diode PCB 9 b b b Break the 10 pin single in line header strip into two parts one of 4 Transistors should be fitted so their outline matches that printed on pins and the other 6 pins Fit to UNDERSIDE of PCB and solder the PCB connections on component side Hi MKARS 80 construction manual 9 Released 5 10 08 V1 2 Fit 2 fuse clips noting they should be fitted the correct way round due to fuse locating tangs C Crystals XTAL 2 5 require their cans grounding before fitting the crystals solder a short length 5 6cm of tinned copper wire or a tinned piece of 22 SWG ECW to the pad provided adjacent to XTAL 2A E 10MHz HC49U Crystal Marked ACT W6 XTAL XTAL XTAL XTAL XTAL j 2 3 q 5 Solder already fitted grounding wire to crystal cans and trim off excess see photo of completed PCB C Fit Q1 into the PCB as far as possible note the orientation shown on the PCB overlay Do not crop the leads right down to the PCB leave about 5mm so the transistor position can be adjusted if required when fitting in to a case IRF510 FET 01 TI Fit the following parts from bag 5 ensure all the sockets are fitted flush to the PCB with no gaps underneath Stereo 3 5mm jack socket CON fo MKARS 80 construction manual 10 Mono 3 5mm jack socket CON PCB Mount
5. c26 9 Oe x P c2 L2 sees E BZH O LJ C26 oe O f A d 3 L3 C34 S PLL zl H 4 SS CG Se nea 603 69 QQ ECH Zi Power switch R35 C49 cpg Rat cu R38 c5a fl GI P A mme KN oz C55 C56 l Si zb 3 f f gt OU ion hl J EE Ga G C71 PES g i Ghote Hee aS pie AOS v Se C92 C36 on gJ gal SI ag 2 ER T5 CR CR D2a x S RIG Ge z OC 7 E G T10 18 EI S MKARS 80 V3 MKARS 80 construction manual 225s Released 5 10 08 V1 2 12 05 07 V1 0 15 06 07 Voltage reading on pin 8 of IC1 corrected thanks to Tom G3LMX LC C42 C46 now 10pF L8 now 10uH Component value changes required due to availability Moved position in manual for adjustment of R29 LCD bias voltage previously positioned at end of alignment instructions Modify fitting LCD Jett most holes are used S Adjustment of bias current R2 changed measurements in example tobe more realistic S LS Schematic Corrected connections on microphone socket in line with PCB no PCB changes MKARS 80 construction manual 26 Released 5 10 08 V1 2
6. BNC socket CoN3 2 1mm DC Socket CON4 Relay BT type RLY Before fitting VR1 and VR2 cut the shafts to required length if using the suggested case the shafts need to be cut so that 18mm is left protruding above the mounting thread Note that shaft length will depend on the types of knobs used Save the pieces of shafts removed so one can be used to later extend the tuning spindle Fit from the component side and connect to the PCB with pieces of cropped component leads Released 5 10 08 V1 2 4k7 Linear potentiometer VRI 10k Linear potentiometer VR Fit the tuning capacitor using M2 5 x 6mm screws NOTE screws must have nuts fitted underneath their heads before fitting so as screw thread doesn t foul the capacitor vanes Dual gang Polyvaricon C57 Fit LED from track side and solder on component side leave the leads long as the LED will require repositioning when the case is fitted The longest lead is the anode terminal 3mm Red LED EDI Fuse 2A QB D Initial testing If necessary wire up the power speaker microphone and antenna leads as shown in section 16 Whilst testing it is best to power the MKARS 80 from a current limited 12 14V power supply on TX a nominal current of about 1 3 Amps is required MKARS 80 construction manual 11 Before connecting power make a careful inspection of soldered joints especially for any solder splashes etc At this point t
7. battery it would also be sensible to fit an inline Released 5 10 08 V1 2 fuse the PCB mounted fuse is designed to protect the radio not the power supply lead Remove the connector cover and slide over both leads Solder the positive lead to the center contact and negative to the outer contact and strain relief when cool carefully crimp the strain relief over both wires and fit the cover Measure the continuity of both leads through to the plug contacts and confirm there is no short circuit between inner and outer Loudspeaker plug 3 5mm mono jack Firstly remove the plug cover and slide over loudspeaker leads Solder one connection to the centre contact and the other to the outer contact cable grip when cool carefully crimp the cable grip around both wires to help give some strain relief Wire size isn t important as currents flowing to the loudspeaker are small polarity of wires 1s unimportant Microphone PTT plug 3 5mm Stereo jack Use has been made of very low cost electret microphones designed for PC multi media use these generally come with a stereo 3 5mm jack plug Remove the jack plug and rewire to a new stereo 3 5mm jack along with a PTT switch the switch should be a push to make type As with the loudspeaker connector remove the plug cover and slide over the microphone and PTT switch leads then solder the wires to connector solder tabs as follows Microphone PTT switch Microphone an
8. excessive force on the leads as this can make the electrolyte leak L1 and L4 Cut off approximately 40cm of 27 out SWG wire and pass half of it through the center of a T37 6 core this counts as the first turn luF 63V Electrolytic Now wind a further 14 turns through the core cio c3 C21 C35 Ico using one end of the wire turn the core over and wind the other end through the core 15 times Electrolytic 10uF 25V making a total of 30 turns Whilst winding pull Can TI the wire tight so the turns lay touching each other Crop the wires to 10 20mm in length 47uF 16V Electrolytic and tin the ends with solder CH cis c68 II MKARS 80 construction manual 8 Released 5 10 08 V1 2 BC337 Transistor Marked C337 40 Oo BS SS ee ee Fit the following from bag 4 D lo ge Co Qs bi bm bee WER eee IC3 and IC4 have 3 legs and look like small transistors Dee ow O 6 fais Ql 022 78L05 EES RE MPSH10 Transistor TERE 09 Q9 Qo S Ki L Fit Q5 with approx 2mm spacing to the PCB LM386N 1 ZTX651 Transistor JO II Bee SR Diodes are polarised devices so can only be fitted one way round 100R Multi turn preset resistor match the band on one end of the encapsulation with the bar printed Ban ff on the PCB 10k Miniature preset resistor 1N4148 Diode R R S Di D Ds D D12 D13 D14 Di5 Set R2 fully ANTI CLOCKWISE and R29 fully CLOCKWISE
9. one of the following ways e Marked directly with their value for example 8 for 8pF and 68 for 68pF e Marked numerically based in Pico farads the first two digits are the value and the third is the multiplier for example 1nF 1000pF is marked 102 1 0 and two zeroes 220pF is marked 221 2 2 and one zero Electrolytic capacitors are marked directly with their value Resistors Values on all the resistors in this kit use a colour code to indicate value MKARS 80 construction manual 18 Colour Black Brown Red Orange Yellow Green Blue Violet Grey White Silver Gold Two resistors used in the battery voltage measurement circuit R21 12K and R23 33K are 1 tolerance types and are therefore marked with 5 coloured bands all other types have standard 4 band markings Tolerance xI x10 1 x100 2 x1000 x10000 x100000 x1000000 0 l 2 3 4 5 6 7i 8 9 Divide by 100 Divide by 10 Released 5 10 08 V1 2 Examples 1kQ 5 1000 Brown 1 Black 0 Red x100 Gold 5 tolerance 2R2 5 2 2Q Red 2 Red 2 Gold divide by 10 Gold 5 tolerance Note that 1000Q 1k 1000000Q 1M 2K2 2200Q 2R2 2 2Q etc Inductors Axial inductors use the same colour code as resistors with their value based in micro Henries for example 8 2uH is marked Grey 8 Red 2 Gold divide by 10 and Silver 10 tolerance All inductors used are significantly larger than resistors so are unlikely to b
10. operation leading to false readings All measurements were made with RF gain at minimum and no modulating audio MKARS 80 construction manual 2 ollector x x OIA NAPePREepYMryloyel LIA N ho ho L2lUnt n oollbN b NJN P UJ 6 oO Released 5 10 08 V1 2 Block diagram and circuit description VFO BFO 6 5 6 2 MHz 10 000150 MHz 3 5 3 8 MHz P E Cut off 4MHz J 3 5 3 8 MHz ie x x 3 5 3 8 MHz Center gt ech gt frequency l 9 999 MHz 0 05 mW Receive 12V 12V 8V 12V Transmit 12V Transmit 8V regulator receive power for oscillator switching stages part of antenna relay MKARS 80 construction manual sds Released 5 10 08 V1 2 The radio uses a single IF super heterodyne architecture with several so called bi directional stages These allow the sharing of all the main functional blocks between transmit and receive mixers IF filter VFO and BFO Receive signal flow The receive signal passes through the transmit low pass filter the switching relay RF gain control and then through a high pass filter in this way a receive band pass filter is not required Filtered an attenuated signal is then amplified and presented to a double balanced mixer constructed from discrete components this mixer 1s also shared with transmit By mixing the received signal with 6 5 6 2 MHz from the VFO an IF of 10 MHz 1s generated Note that the VFO works backwards a 3 5 MHz tuned frequ
11. 7 ev gt 1 Top T p 4 T on T37 6 4 8uH BC547 c53 T AN c59 T wi IE polyester lt 7 V GOND R30 R31 y vyv SZ YZ JA Vo y Antenna 180k 188k R49 R50 she tk R76 a EE z TE oaae 7 sN YANE ap i Sch Ca ces S 7 4 LI LF L4 S7 3 T on T37 6 32T on T37 6 30T on T37 6 Teone 00nF Ko 3 3 M 012 Gig E 10pF 2 7UH 3uH ZZ Je Z BC547 Lo ala XTAL1 BC547 100nF M BC547 AA TN ee oe ss Wey kA Q16 T anF Se R43 vv Z Vy Z V yg b V Lja vw S rc eS ae Si c22 eg ez Con Can C34 Em GI D4 1 4 ace c7 ca S pF S6Q0F 560pF S OpF Gert 560pF 39 pF 470pF 33V 400nW os 3300F 4700F 100nF i g KZ W C62 o R59 2200F 100nF 100R 25T preset Ka SA K Vv Es KS K 62 polyester w 1 kd 33V 400mW c45 Cap R45 i k s oj o EEN 100pF NPO 5250pF NPO V 7 ie Se ee Di SS PC1602F 4 bit display 10R ZZ os lt 1aMHz ik 15 EE 220pF R23 BS 33k 1 V R58 R77 es i Wd NZ LA lt 7 H2l3 220R 220R Vad o e WZ SZ c73 A RS a 22pF e D mrt yn wor Last Vv Vv WA RADA AA x RLY1 b Cal aw oO oo fo E x 0 pF Ic3 Dip 7 KE Leppe F B p ho LM78L 5ACZ a a oe lt 1M4148 ER out LL Es Rx L tr 14 FEH E Rie LH tev 5 5 30pF 73 08 4R7 ori Fa Ria v R29 2 at Cas te ER Gnd c51 i TUF 16v D cz S Sua Tv Sud 12V 3 e out H 220uF 16V H 100nF T SW Vv 1 JI a VY Rat lt SZ Cen A 100nF p 2 2k 1 Bad esi SEH Sour tev 2 ui ie Vv S
12. The MKARS 80 QRP 80M transceiver Construction and user manual ee AGT Author Steve Drury G6ALU AME List of contents Pn ATT Section Page Ska 3 T S omg no S i SEN 1 Specifications 2 ges s f mse 2 Introduction 2 3 Construction 3 4 General construction practice 3 5 Component placement 4 6 Initial testing 11 7 Alignment 12 8 PCB options 13 9 Boxing up 14 10 In use 15 11 Plug and socket fitting instructions 16 12 Component Identification 18 13 Fault finding 20 14 Block diagram and circuit description 22 15 Circuit diagram 24 16 PCB overlay 25 17 Change log 26 MKARS 80 construction manual ei Le Released 5 10 08 V1 2 Features Full 80M LSB coverage gt 5 Watts output power Frequency display with Huff and Puff circuit Modulation monitor helps stop over modulation Volt meter useful for battery operation Reverse polarity protection fuse protected Typical Specifications 13 8V supply Operating Frequency 3 5 3 8 MHz RF output gt 5 W Sensitivity MDS better than 1 uV IF frequency 9 999 MHz Audio output Current consumption Approximately 0 5W Receive 120 mA no signal Transmit 1 2 amps Supply voltage 10 16V Microphone Low cost electret type Loudspeaker 8 Ohm will work into 4 Ohm MKARS 80 construction manual 2 Introduction As significant interest had been shown by Milton Keynes Amateur Radio Society members for a transceiver co
13. ap diode actually a zener used as a varicap in the VFO section An A D input of the micro controller is used to measure and indicate supply voltage via the LCD display Released 5 10 08 V1 2 Circuit Diagram RX 12V gt RX 12V gt RX 12V R69 Ret 100R 100R C37 coa R71 R ETET 100nF Tone Kn E T L3 C44 cee CU oe TOonF 1200F 1200F 1N4148 Res Ree 220R ca m ain 220R II A 1e0nF v CG KS me o CS c26 Co 220uF 16V 1 2nF BONF WY YV get i A GE Si if i if xy 4k7 Lin POKER l 1N4148 ci cal R54 100nF 100nF Bei 1 an a R74 a13 cea f S SC R6 mix MPSH10 100nF p Ka V gv Ce J er A TX 12V t 10 nF V 1 he ai
14. ated on the template use good engineering practice start with a small drill and work up in size Note the following e Ifthe recommended case is being used the control shaft and BNC connector holes will need to be elongated to allow the PCB to fit e Ensure that when plugged in the DC connector outer contact can t touch the case e Ifthe PA transistor mounting hole doesn t align properly it is permissible to open the hole up slightly if stressed the transistor legs will fail sometime in the future These lines should be alligned with each other To cut the display window without special tools I would recommend drilling many holes close to each other just on the inside of the window then using a pair of side cutters join them up The window can then be squared up using a file E When all holes have been cut trial fit the board to the case and if necessary re heat the solder pads on Q1 PA transistor to align its mounting hole with that drilled in the case Released 5 10 08 V1 2 Note that when fitting the PA transistor into the case a heatsink washer and insulator must be used place the insulator no thermal compound is required between transistor tab and case fit plastic insulator through tab of transistor and into hole in case Then fit an M3 x 10mm screw from the outside of the case and secure with flat washer serrated washer and M3 nut see photo Silicon insulator Plastic M3 x 10mm insulat
15. correct the drift and there will be a sudden change m tuned frequency RF Gain The RF gain control determines how much signal is applied to the receiver this has the same effect as adjusting the AF gain volume control on a conventional radio As this simple design doesn t MKARS 80 construction manual 16 incorporate an AGC circuit the control has to be adjusted for a comfortable listening volume and may need adjustment between different stations in a QSO WARNING Be carefull when using headphones as volume is dependent on strength of received signals and at the very least this could surprise the operator when tuning through a local station Modulation indicator This LED extinguishes at about the point the PA transistor saturates running the output transistor into saturation can cause splatter across adjacent QSOs Splatter is actually intermodulation and is caused by the output stage becoming non linear and mixing frequencies within the wanted spectra causing nearby unwanted signals Whilst transmitting the indicator should momentarily extinguish on voice peaks Fitting Plugs and sockets Power connector 2 1mm DC plug These are available in two lengths either is suitable with the case recommended but the long type may be required if the case has thick walls It is very wise to use colour coded lead red and black to avoid any accidents Use a lead suitable for carrying 2 amps 1f running from a
16. d Dt Se ots D Se 5V6 400mW SE Nw nes BC547 e ik c87 e C78 BS oonF ie R2 R32 m re 10k 100R Ree R55 D R72 220R R53 220R Lg God Tk Gee Rea 0nF i EN T3 ei TeonF e a Leem S7 R63 Se Keng t Toone REZ 220R XTAL2 XTAL3 XTAL4 XTALS cos 10k 470R TT 188nF v y WAL nL nl Y VY VY V7 TI Ge ee e e e e UU H D Ai TX 12V K eeh c4 e e V Co d WS SZ 7 7 at Si ES ege RLY1 c 100nF LS c76 ca4 C104 R92 IRFB10 R81 gt R22 R37 120R 1000F 220pF 1000F 100R e TX 12V EE S r c32 t R84 c92 K K S7 e NZ oe K toane aia ET Tagan s o5 a J rt ZTxX651 a D28 D19 N4148 IN4148 L c55 L7 et La cee Shee a9 T8uH 100pF 18uH 20oF mg 20pF Nw mmz MPSH10 ANAA gt AMA YN ote R82 SC SE ed 623 1N4148 BR e __ IBAF EN D2 1N4148 Bake R39 R85 S RIS TI R5 c43 e 22R 470R R33 100nF c56 Co Kg cov ia 100R c54 InF ces Ca ES IN4 148 MA oC Set SA e Ke Co AM R3 in Mod LED Anode R36 108nF R91 a ES CH K d ae T 2k2 Mod LED Cathode 020 A ER MPSHLO ep II SCH S7 VY S7 VY Leem l 10 nF aoe Ge y V 10nF C64 7 bm geg 108nF Q22 v R35 Br Ge BCS47 cs C49 Q1a ie ik p L t 1B nF BC547 SZ _ Gel R86 D 220R Rez z See 2V7 Agen R4 R79 nT TG loon ne c1a2 ik kl Nw cial W Es x D c63 100nF R41 47uF 16V KZ epp Arie hi t M Sud 12V R96 Cu 470R R89 VR2 Gem L5 220R R88 1 42 Cie SS git SF SZ 100R BV SCH Ok Lin pot
17. d PTT ground Plug tip Middle contact Outer contact When the soldered joints have cooled the cable retainer should be carefully crimped over all wires and the cover screwed in place MKARS 80 construction manual II Note that a DC bias is provided on the microphone input by R17 if the user insists on using a dynamic microphone this resistor should be removed BNC connector The connector shown here 1s a typical low cost BNC type Over the cut end of RG58 coax slide the clamp nut washer and seal Strip the sheath off over long approx 15mm and slide on the tapered collet Pull braid back over tapered collet and trim trim the inner conductor length to 7 5mm and then strip the dielectric to 5mm in length Fit the inner contact and solder through small hole Released 5 10 08 V1 2 Fit body and tighten clamp nut finally check that there is no short circuit between inner and outer contacts and that inner contact is in correct position Component identification Components have been packed in to 6 bags the contents of these bags and order of assembly have carefully been chosen so similar components shouldn t become confused For fault finding it will be necessary to correctly identify components and their values after the radio has been built methods of marking component values are given Capacitors Most of the small value capacitors ceramic and Mylar used in this kit are marked in
18. e confused axial inductors only have one failure mode open circuit which can easily be identified with a multi meter set to measure resistance Diodes All diodes used are axial and have their cathode end marked by a band on the encapsulation Values are marked on the bodies although for the small glass diodes zener diodes and 1N4148 types they will be hard to read without a magnifying glass MKARS 80 construction manual 19 Transistors and Ics View trom underside of package TO92 and E line terminal identification Lead identification a BC337 BC547 MPSH10 ZTX651 78L05 78L08 KL Tab Drain IRF510 FET terminal identification UU DS Released 5 10 08 V1 2 LM386 is similar to PIC16F818 but only has 8 pins gt Wm co W co Wm co LL T Wm d Fault finding Most faults are due to poor soldered connections or components misplaced it is very rare to be supplied with a faulty component Before making any measurements look carefully for any poor soldered joints short circuits or incorrectly fitted components Should fault finding be necessary a table of voltages is given below transistor voltages were measured both in transmit and receive MKARS 80 construction manual 20 Released 5 10 08 V1 2 Voltage tables Receive Transmit Transistor SS Q Or OS Notes e Value will depend on setting of bias control Measuring this point can affect circuit
19. ency requires a VFO frequency of 6 5 MHz and a tuned frequency of 3 8 MHz requires a VFO frequency of 6 2 MHz The amplified IF signal is then filtered by a 4 pole crystal filter at 9 999 MHz before again being amplified and presented to the BFO mixer When the IF signal is mixed with the output from the BFO an audio signal is produced this is then amplified and supplied to the loudspeaker A mute circuit operates in transmit to avoid feedback between microphone and loudspeaker Transmit signal flow Audio from the microphone is first amplified and then fed to the BFO or carrier insertion oscillator the frequency spectra generated is first amplified and then filtered by the IF filter shared with the receiver Amplified IF signal 1s presented to the main mixer where it 1s translated to the output frequency again amplified and then filtered by the band pass filter Three more stages of amplification follow before the signal is passed through the transmit receive relay then through the low pass filter to the antenna MKARS 80 construction manual eee Frequency display and Huff and Puff A micro controller counts the VFO oscillations with a 40mS time base derived from the BFO a correction voltage 1s also derived form the comparison of the counted down VFO input and the internally generated 40mS time base The correction voltage is generated by an internal PWM pulse width modulator and after filtering is applied to a varic
20. ent will rise do not transmit for more than a few seconds if Q1 isn t fitted with a heatsink or it will overheat R59 and C103 mixer balance connect a sensitive power meter and dummy load to the antenna connector With power connected slowly insert the microphone PTT plug until the transmitter is operated but BS 2 not modulated by the microphone alternatively plug in a stereo jack with all contacts grounded A small reading may be noted on the power meter adjust R59 to reduce this to zero There are two possible methods to further improve the mixer balance 1 Tune in to the carrier with another radio and adjust R59 and C103 for minimum signal or S meter reading 2 Connect an oscilloscope to the antenna connector and adjust R59 and C103 for minimum waveform note that both these adjustments are inter reactive they effect each other PCB Options Power switch The PCB incorporates a facility for fitting a power switch the RF gain control may be replaced by a switched 4k7 linear potentiometer and the power switch wired to the marked pads For the switch to function the track needs to be cut with a sharp knife where indicated Internal Loudspeaker A small internal loudspeaker can be fitted it is best to position this away from L5 to avoid the magnet de tuning the VFO Connections are provided for the loudspeaker the polarity being unimportant the internal loudspeaker will be disconnected
21. he micro controller and display should not be fitted as these components can easily be damaged by wrong voltages applied to their pins Measure between supply positive and ground with a multi meter on Ohms range to ensure there is not a short circuit typical values will fall in the range 1k6 to 2k0 Note that if you reverse connect the meter IE red lead to ground and black lead to positive the reverse protection diode resistance will be measured Make sure R2 1s set fully anti clockwise Connect the loudspeaker Connect 12 14V and check for any obvious fault symptoms loud noises or smoke Assuming all is OK measure the 5V regulated supply at R34 see photo it should be 5 0 25V and the 8V regulated supply at VR2 which should be 8 0 4V If either is incorrect remove power and investigate the problem before continuing Connect an antenna and advance the RF gain Depending upon band conditions and the gain of the antenna there should be either stations or noise heard the RF gain may need to be advanced fully clockwise to hear noise when the band is poor If all is OK remove the power and fit the micro controller Released 5 10 08 V1 2 e2 Now install the display firstly fit the display using a single screw in its top left hand corner a M2 5 x 12mm screw is passed through from the PCB component side and held in place with a nut On to this is screwed another nut the display and finally another nut Note
22. is not suitable as it exudes acetic acid whilst curing The correct adhesive doesn t have any smell BN43 2402 5T Trifilar wound 38 SWG ECW Me eg MS Ee T1 and T3 these have two windings each with 5 turns of 38 SWG wire First wind 5 turns through the core from one end of the transformer and crop the leads at 20 40mm in length then turn the transformer round and repeat with another 5 turns from the other end It is easiest to tin these wires before fitting the transformer to the PCB Tl Ts Released 5 10 08 V1 2 T2 is wound using the same method as for T1 and T3 but the windings have three turns of 22 L2 is wound in a similar way with the same 27 SWG wire but has a SWG wire on the larger BN43 0202 core total of 32 turns Keep the turns tight but it doesn t matter if several turns overlap L5 use approximately 50cm of 33 SWG wire and wind using the same procedure as the other toroid cores with a total of 40 turns space the wires evenly around the core SR HE L3 wind 2 turns of 27 SWG wire through the holes T37 6 32T 27 SWG ECW of a BN43 2402 core and tin the leads L i T37 6 40T 4 8uH 33 SWG ECW o Electrolytic capacitors are polarised so may only be fitted one way round By convention the PCB is marked with a symbol the lead of a capacitor is longest the capacitor sleeve is also normally marked Fit the capacitors against the PCB with zero lead length but don t put
23. l them out from the topside A small solder sucker or de solder braid can be used to clear the holes out ready for a replacement component to be fitted When soldering the component leads it will be noticed that the solder wicks up the hole through to the top surface this is normal For a start place just a few components in place before soldering them as experience grows you may find it more productive to fit a larger number at a time As each component is fitted put a mark in the box provided it s very easy to forget the last component fitted especially if you are distracted If you make use of the component overlay you will find it helpful if components are highlighted as they are fitted Components are taken from one bag at a time keeping the others sealed some component types are split between several bags so indistinguishable parts don t become confused especially zener diodes and trimmer capacitors Everyone has their preferred method of retaining components prior to soldering I pull the leads through with long nose pliers and put a bend in the component lead to stop it falling out of the board A good policy is not to crop leads until they have been soldered this should stop you from missing any soldered joints As this is a PTH board leads can be cropped quite close to the PCB without damaging the soldered joint Released 5 10 08 V1 2 Note that the PCB shouldn t be cleaned with solvents as residue may enter
24. n VFO to maximum frequency and check that it is possible to tune above the top of the band If desired the total tuning range can be adjusted with a trimmer capacitor on the back of the Polyvaricon Moving the capacitor into mesh will reduce the range and moving out of mesh will increase the range note that after adjusting this capacitor the frequency will need adjusting by C38 Adjust for required tuning range Released 5 10 08 V1 2 MKARS 80 construction manual C83 BFO there are two methods of adjusting the BFO frequency either are acceptable 1 Using a frequency counter adjust C83 for a frequency of 9 9999MHz measured at TP 1OMHz 2 Accurately tune to an SSB transmission on a known frequency and adjust C83 for a properly resolved signal S C54 C68 and C79 band pass filter the setting of these capacitors is not critical and may be set as shown in the photo S R2 PA bias current disconnect the antenna and connect a dummy load suitable for 5 Watts Connect an ammeter in series with the radio and power supply capable of reading 3 amps Whilst making this adjustment do not speak or make other noises into the microphone press the PTT and note the current drawn Adjust R2 for an increase of 50 SmA For example before adjustment R2 fully anti clockwise the current was 230mA in this example when correctly adjusted the current will be 275 285mA Note as the components warm up that the curr
25. nstruction project I decided to produce a kit for the Epiphyte originally designed by the QRP club of British Columbia Unfortunately this design used several obsolete components whilst searching around I became aware of the BITX20 designed by Ashhar Farhan The BITX20 is a low technology transceiver designed to use simple components and 1s easily adapted to other bands I quickly manufactured a variant for 830M version 1 The radio presented here is a development of that now at version 3 Many changes have been made through my experience with the first prototype the original design philosophy was to keep the radio very simple and basic but I quickly appreciated the benefits of a frequency read out and Huff and Puff VFO stabilisation The original design didn t have an RF gain control so would overload very easily with the large signals on 80M the volume potentiometer was therefore moved to the front of the receiver becoming an RF gain control Another requirement was for all components to be mounted on to one PCB keeping wiring to a minimum and PCB cost low The prototype used Toko coils but many of these are now hard to obtain so either fixed inductors or inductors using readily available and low cost cores have been used throughout Released 5 10 08 V1 2 Construction These instructions have been targeted at those with some construction experience and who can identify the different components Where out of the ordinar
26. or gt screw Serrated washer mm flat washer Flat washer have catered for two methods of fitting a front panel with a little thought I m sure there are many more For those wanting to design their own front panel critical hole dimensions and spacing are given on the drilling template 1 A PDF file of a front panel is provided this may be printed and glued double sided tape perhaps to the front and then covered with a sheet of acetate overhead projector film trapped under the four fixings screws MKARS 80 construction manual 15 2 A negative image is provided this can be printed on to acetate or a bubble jet transparency by reversing the image the non printed side is nearest the user so protecting the writing The builder is encouraged to personalise the front to their own taste to add some individuality Frequency Supply Huff and Puff voltage LCD Dis play correction The PCB is secured in place by 4 M3 x 6mm screws with flat washers under the heads Secure the BNC to the case using the serrated washer and nut supplied Fit three knobs as required note the shafts are 6mm in diameter Final air test Attach an antenna and arrange a contact with a local amateur on the 80M band to confirm the radio operates as expected In use Firstly it should be remembered that the MKARS80 is low cost and of a relatively simple design its functionality cannot be compared with a complex commercial transceive
27. r That said great enjoyment can be had if its limitations are realised Released 5 10 08 V1 2 After powering on best frequency stability isn t reached until the temperature within the case has stabilised the Huff and Puff circuit will keep the radio on tune in the short term but may need adjusting a few times during the warm up period Tuning The VFO is capable of covering the whole UK 80M allocation but due to the VFO frequency being below that of the IF the tuning works backwards I e clockwise rotation decreases the tuned frequency Once the approximate frequency has been tuned with the main tuning control the fine tune control may be used to get within 25Hz of the wanted frequency It will be noticed that the Huff and Puff circuit will try to hold the frequency as you adjust the fine tune control this hold will be broken when the actual frequency is more than about 100 Hz different from that displayed Once the lock is broken there will be a delay of 8 seconds before the Huff and Puff again tries to hold the frequency steady The Huff and Puff circuit is able to compensate for about 1 5kHz frequency drift the position within the lock range is shown by the bar to the left of the battery voltage If this tuning bar reaches either of the extremes the VFO should be re adjusted Remember that if the displayed frequency is more than about 100Hz different from the VFO frequency the Huff and Puff circuit will stop attempting to
28. r in c31 les s eee ee size if measured by a multi meter they will read a very low resistance C80 Cd o O ee es w w mw 0 ES Co Io IO Fit the following components from bag 3 e EE np mm BEES Res SEN a SSES ce e Fee EE erer Ee om a S Le co Wo c43 cz BSG TE ee eee eae d i x 560pF Ceramic 561 560pF Ceramic S61 EI c20 c22 c23 c33 K ee S 33 C26_ c27_ C29 BW WW d C61 c62 Co4 77 cs cs2 Ice c87 css cso c91 CO Io O Tee y if iH iH C102 EE C105 E 10uH Axial inductor Brown Black Black Silver WW WE ue 9 50pF Open trimmer Non enclosed trimmer capacitor Winding the inductors and transformers This is probably the trickiest part of the build although with a little care 1s not too difficult The thickest wire has the lowest SWG Oe em ee eee Pe number 38 SWG is the thinnest 22 SWG the thickest Fit all the MKARS 80 construction manual 6 Released 5 10 08 V1 2 toroid inductors vertically against the PCB refer to the photo of finished radio T4 T5 and T6 These transformers are trifilar wound that is 3 wires are wound through the ferrite core at the same time First cut three pieces of 38 SWG wire the thinnest supplied about 30cm long and at one end tightly twist all three together for about 12mm snip the end off and solder together this will make it easier to th
29. read the wires through the ferrite core The remaining length may be lightly twisted to stop it getting tangled Thread the soldered end through one of the holes of a BN43 2402 core the smallest core see photo leaving about 10cm remaining then thread the wire back through the other hole this is one complete turn Loop the soldered end through a further 4 times to make a total of 5 turns Trim the wires back to about 50mm in length splay apart and tin the ends with solder Now the ends of each of the three wires has to be identified To do this use a multi meter on the ohms or continuity range when the first wire has been identified bend it backwards out of the way Locate the MKARS 80 construction manual 7 second wire trim these two ends to about 30mm in length and now confirm the last two ends belong to the third wire and crop to about 15mm in length These wires are then passed through the PCB longest first and shortest last anchor the transformer into the PCB by bending 4 wires over against the board Trim the remaining 2 wires to just a few mm in length and solder in place be careful to make sure that the enamel burns away and the wire tins properly Once the first two wires have been soldered in place the other four may be cropped and soldered After the radio has been completed and tested the transformers may be fixed into position with a little non acidic silicon adhesive note that bathroom sealer
30. that the PCB spacers supplied are 12mm long this means the display MUST not be higher than 12mm above the PCB or it will be pressed against the case causing damage When you are happy with the distance pass pieces of tinned copper wire through the display connections and push them into the socket strip beneath the LCD should be moved so the left most holes align Straighten the display compare its top edge with the edge of the PCB and solder them to the display This will make the display pluggable which is desirable so soldered joints underneath can be accessed Look between the display and main PCB and confirm that there are no wires shorting between the two you may wish to fit a cardboard or MKARS 80 construction manual 12 plastic insulating sheet under the display to guard against any accidental short circuits PC1602F LCD Display Dap Re connect 12V and adjust R29 display bias whilst monitoring the LCD display slowly turn R29 anti clockwise until the background extinguishes leaving just the characters The display should first show a welcome message followed by the frequency and supply voltage Alignment Set the VFO frequency range the UK 80M allocation is 3 5 3 8MHz As viewed from the front track side turn the Polyvaricon C57 knob fully clockwise _ frequency and adjust C38 so the frequency displayed is just a little lower than the lower band edge 3 450MHz is suggested Turn the Polyvarico
31. the trimmer capacitors and any surface treatment designed to aid soldering will be removed Where possible fit the components so their values are easily readable Some components MUST be fitted in the correct orientation as they are polarised this will be indicated in the text Save all the cropped leads as some will be needed to fit the display later in construction and may also be used as test loops The components are packed in six bags each bag contains a list of contents which will show any substitutions that have been made Component placement Resistors are quite small and are identified by four or five colour bands if in doubt use a multi meter to confirm their value From bag 1 fit the following components 4R7 Resistor Yellow Violet Gold Gold R0 R89 R8 R24 R36 R46 R62 ROT MKARS 80 construction manual s a 22R Resistor Red Red Black Gold pe R9 R57 Is ESCH B SER Resistor Green Blue Black Gol Blue Black Gold RI SEENEN R52 R61 R69 R7 R81 R83 R88 R9 R7 R4 R55 R58 ROO R63 R66 R68 R77 R82 R84 R86 R93 RI R25 R70 RIO R3 R6 R9 RI3 RIB R26 R34 R38 R39 R47 R50 R51 R53 R65 R67 R733 R78 R79 R80 R85 B Tse Released 5 10 08 V1 2 2k2 Resistor Red Red Red Gold 100pF NPO Ceramic Marked 101
32. when the external speaker socket is used Released 5 10 08 V1 2 Internal battery PCB pads are provided for connecting an internal battery if desired a i k 7 D r F i H Wi a jp Ba d a d washer em M3 x 12mm stand off washer 3mm Serrated 7 e washer Se M3 Nut the negative terminal is isolated when an external power source is plugged in note that there is no provision to recharge internal batteries Boxing up Fit 4 M3 x 12mm hexagonal spacers to the corners of the PCB a flat and serrated washer should be fitted under each nut C Cut the knob extension to length and fit to the tuning capacitor shaft this is a short length of plastic air pipe it allows one of the cut off potentiometer shafts to be used to extend the Polyvaricon shaft Don t force too much tube over the shaft as the pressure required could damage the capacitor E A metal case must be used for screening and to provide Q1 with a heatsink Print out the drilling template and confirm the size is correct by measuring the printed dimensions Stick the drilling templates to the outside of the case aligning the reference edges with the INSIDE surfaces of the box this is important for the templates to be universal no account has been made for case thickness instructions are printed on the templates Possible adhesives are PVA glue and double sided tape MKARS 80 construction manual 14 Drill all holes to the sizes indic
33. y parts have been used a short description follows the component value All components except for the display its socket and modulation LED are mounted on the component side of the board The PCB silk screen gives the component locations in cases where this is difficult to read please refer to the printed overlay that is larger than actual size Note that components are numbered from left to right then top to bottom of the board If you have difficulty in locating a component position place a straight edge across the overlay and look along its length in this way components will be easy to locate The PCB has been designed to accommodate the components supplied so if it doesn t easily fit ask yourself if it belongs there General construction practice Leaded or lead free cored solder may be used the solder must be designed for electronics do not use plumbers solder or additional flux as the flux is very corrosive I use 22S WG 0 7mm multi core type solder that seems most suitable for this type of work A double sided plated through hole PTH PCB has been used this has the advantage of greater stability and makes dry MKARS 80 construction manual 3 joints very unlikely however incorrectly fitted components can be very difficult to remove so it s important to fit them in the right place first time If a component is inadvertently fitted incorrectly it is easiest to cut off its leads apply the soldering iron and pul
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