Building the KD1JV MMR-40 "dead bug" style
What is the MMR-40? It is a 40 meter rig with SSB (voice) and CW (Morse code) operating modes. This is a low power (QRP) rig with up to 6 watts CW or PEP (peak envelope power) output. This rig was designed for the ARRL Homebrew Challenge, the goal of which was to come up with a functional CW/SSB rig design which could be reproduced for under $50.00 using common hand tools and a minimum of test equipment. The MMR-40 was one of two winners for this contest. In theory, the parts cost of all new parts in single piece quantity is about $32.00. The actual out of pocket costs will be some what higher, because of the shipping and handling costs to get the parts to you. The cost of wire and any tools you may need to buy are also not included in the base price. The full parts list with distributors part number is located at the end of this page.
The MMR-40 is also available as a compete kit with double sided circuit board and cabinet for a professionally looking rig. The kit is available from Hendricks kits www.qrpkits.com
Kit version of MMR-40 board
This document will attempt to provide the basic knowledge needed to build the MMR-40 dead bug style from the schematic and is geared for the novice builder. However, painfully detailed step by step instructions are not supplied. To do so would make this a much longer document than it already is and would drive me nuts writing. Helpful hints are frequently given for things that are not all that obvious. It is assumed that you are intelligent so can figure out some details on your own, have reasonable mechanical skills and dexterity. You must often work with both hands, holding a part in one hand and the soldering iron in the other. Sometimes it helps to be able to handle three things at a time!
If you have never built a piece of electronic equipment before and have little or no knowledge of electronics in general, there are a number of things you need to learn before you begin. First, you need to be able to read a schematic and relate the schematic part symbols to the actual physical part. Once this is understood, assembly is simply an exercise in mechanics. It is not all that important that you understand the function of each part or how the circuit works as a whole . What is important is that it is wired correctly. Understanding how the circuit works is important if you need to figure out why it doesn't.
It is suggested that additional resources like the Internet, the ARRL handbook and similar publications be consulted for a more in depth discussion of schematic symbols, what the parts actually do, basic circuit theory and building methods.
Possible construction methods:
There are three construction methods you can choose from to build this rig. The best method is to make a printed circuit board. The second best is to make a pesudo circuit board, and finally to use the classic "dead bug" on ground plane method. Each method has its advantages and disadvantages.
Printed circuit version:
For those of you who know how to make a printed circuit board, this is perfered to building the rig dead bug style. You will end up with a better looking and most likely more reliabe rig this way. Single sided board artwork can be down loaded as a pdf file. The layout is shown as "through board view". This view allows printing directly to toner transfer film and the proper image reversal is done when you transfer the image to the board. This view is also consistant with photo sensitive boards, as you want the printed side to be against the circuit board.
You may have to check your printer preferences to make sure it prints to scale. X and Y reference distances are on the drawing so you can check to see that the scale is correct. A second pdf file shows the part locations, jumper locations and part values. Even though the layout is for a single sided board, using a double sided board is a good idea. The top side will have to be masked so it doesn't etch ( I cover it with vinal electrical tape) and then all the holes countersunk for parts which do not connect to the bottom ground. The ends of all the parts which connect to ground are soldered to both the bottom and top side of the board. Using a double sided board will allow mounting the PTO coil on the top side of the board. Note that some of the point to point jumpers required are best made on the bottom of the board. Down load board layout file Down load parts placement layout file
Pesudo circuit board method:
This method involes drilling all the holes for the parts in the circuit board matterial but with out etching the board. Instead, all the connections are hand wired. To use this method, you will need a drill press and a selection of carbide pcb drill bits. Carbide drill bits can be bought as surplus or resharpened bits from a number of sources at reasonable prices. Keep in mind these bits are very fragile and break easialy with any side torque, so a drill press is required if you expect to use them to make more than one hole. Do not be tempted to use cheep steel twist bits, as these will burn up and get dull after only a few holes have been drilled.
Print a mirror image of the board layout diagram. Tape this to bottom, copper side of the board and drill all the holes. Now you have to counter sink all the holes which do not connect to the ground plane. This is to remove the copper from around the holes so you can attach wires to the componet leads which need to be inter-connected and not short out to the copper ground plane. For counter sinking, you can use a 0.1" dia carbide router bit or a standard 1/8" drill bit, as you are not drilling all the way through the board.
Once all the holes have been drilled and countersunk, you can start installing parts and making the interconnections between them. Print a new copy of the board layout (also a mirror image) to use as a wiring guide, duplicating the connenctions normally made by the copper tracks.
Dead bug method:
This method is discribed in detail later in the document.
A schematic is a road map showing how a circuit is wired together. Parts are shown as a symbol and connections between the parts as lines. Some lines cross. If two or more lines cross and there is a dot at the junction, it means these lines are connected together. If there is no dot where lines cross, there is no connection between them. A good schematic is drawn so that there is some sense of signal flow. Typically, this is from left to right with inputs on the left and outputs on the right. A good physical placement of the parts will try to follow the same general layout as the schematic, as much as maybe possible.
With this basic understanding of how the circuit is represented, all we need to know now is what physical part each symbol represents. Any electronic circuit will use basic parts like resistors, capacitors, diodes and various active devices, such as transistors, FETs and ICs. The following will show the schematic representation of a part and how to determine its value.
Resistors are little "dog bones" with a wire coming out of each end. They are bi-directional so it doesn't matter which end is used to connect to some other point. The value of the resistor is marked by color bands. The first three bands indicate the numerical value and the fourth is the tolerance. 5% resistors, which are the most commonly used, have a gold band as the last color and is used as the marker to determine in which direction the other colors are read in. The first two colors are read as numbers and the third color indicates the number of zero's which follow. Therefore, a resistor with the colors Brown Black Black Gold is a 10 ohm 5% resistor. A resistor with the colors Red, Red, Red is 2200 ohms or 2.2 K. A resistor with a value of less than 10 ohms will have a gold or silver band as the third color. In this case, a gold band means the first two digits are multiplied by 0.1 and a silver band by 0.01. Therefore a 1 ohm resistor will be marked Brown, Black, Gold, Gold and a 0.01 ohm resistor would be Black, Brown, Silver, Gold.
Capacitors come in a variety of shapes, sizes and types. The types used in the MMR-40 are Ceramic Disks, which are round, flat disks and usually have a tan or brown color. Multi-layer ceramics or Monolithic (Mono) are squarish and usually yellow or occasionally blue. Mylar Film, which are often green or white in color and finally, Electrolytics which are round cans with a plastic wrapper. The first three types, disk, mono and film capacitors have no voltage polarity so it doesn't matter which lead goes to what part of a circuit. Electrolytics are voltage polarity sensitive and can actually explode if improperly installed. The long lead is always the positive lead and the negative lead is marked with a black or gray stripe along the body of the can.
Values of capacitors are always marked with two or three numbers. The first two digits are the integral value and the third digit is the number of zero's which follow. The value is in picofards (pfd). Sometimes there will be a letter following the numbers and this can either indicate the type of capacitor or its tolerance. The meaning of the letter varies between manufacturers, so no hard fast rules apply to this letter. NPO type ceramic disks usually have a black dot on the top edge of the disk.
Therefore a 22 pfd ceramic disk capacitor will be marked "22". A 220 pfd cap would have the numbers "221" marked on it. Some monolithic caps will have have a third digit, even if the value is less than 100. If the last digit is a 0, that means no zeros after the first two digits. A 0.01 ufd cap will be marked 103 and a 0.1 ufd cap 104 and so on.
Here is where things get interesting. There is a wide range of semi-conductors and the types of packages they come in. These parts must be wired in correctly or they will self destruct (more often than not). Semi-conductors may be transistors (NPN and PNP types), field effect transistors (J-FETs or MOSFETS), Diodes and Integrated Circuits (ICs).
Bi-polar transistors come in two flavors, NPN and PNP. NPN types require a positive voltage on the base in respect to the emitter to function. PNP are the reverse, requiring a negative voltage on the base in respect to the emitter. J-FETs and MOSFETS also come in two flavors, N type and P type. Like the Bi-polar types, N types use a positive gate voltage to turn on and P types a negative voltage.
The pin outs for transistors and FETs shown below are for the types used in the MMR-40.
Intergrated Circuits (ICs)
IC pin outs follow a strict pin numbering scheme. Pin 1 is always in the upper left corner and the pins are numbered in a counter clock wise direction down the left side and up the right side. The Pin 1 end of the part is marked with either a dot or dimple next to Pin1 or with a notch at the end and center of the package. Often there is both a dot and a notch.
Diodes are one way gates. Current can flow in one direction and not the other. Current flows from the Anode to Cathode. The Cathode end is always marked with a black band around the body of the part, as shown in the above diagram. Small signal diodes are generally in a glass package, while higher current rectifier diodes are in a black plastic package. There is also a special kind of diode called a Zener diode. When a positive voltage is applied to the cathode in respect to the anode, current will start to flow through the diode. The voltage it takes to start current flowing through the diode is dependent of the voltage rating of the diode. The symbol for a zener diode has two extra little lines added to the ends of the vertical line the arrow of the standard diode symbol points to.
Building "Dead Bug" style:
Circuits built on a solid copper ground plane, usually a piece of copper foil laminated to a fiberglass board, and in which the transistors and IC's are mounted with their legs sticking up in the air is called "dead bug" construction. This is because these parts look like dead bugs on their backs. Makes sense, eh? Passive parts are either connected to the the IC and transistor leads, soldered directly to the copper ground plane foil or are suspended in the air. This is a three dimensional construct. This will make more sense later when you view the pictures of the circuits as they are built.
Before you can actually start construction, you need some tools. At a minimum, you need a pair of needle nose pliers, side cutters (Dikes) and a soldering iron, with stand. A hot glue gun can be handy here and there. The type of needle nose pliers and side cutters usually sold at hardware stores are too big and clumsy for fine electronics work. You want pliers which come to a fairly fine tip and cutters with a small head to get into tight spaces. A hobby knife such as an Xacto with #11 blade is useful, as are tweezers. A soldering iron with a 25 or 30 watt rating is a good general purpose iron. Get one with an iron clad tip, as this will last longer than an unplated copper tip. If the iron is sitting unused and on, keep a little solder on the tip. If you need to clean the tip of excess solder, only do it just before using. Do not clean the tip and then put it back in the holder and let it sit for any length of time, as the plating will burn off or become tarnished. Be sure to get a soldering iron stand. It is not a good idea to have a hot iron loose on the work bench!
Proper soldering is a fine art, but is not too hard to master. Heat the junction to be soldered together with the tip of the iron for a second or two, then apply the solder from the side opposite from the soldering iron tip. The biggest mistake novice builders make is to use way too much solder. I like to use 0.020" dia solder instead of the more common 0.032" type. The smaller solder allows better control over how much solder is used. You just need enough solder to make the leads stick together or attach to a printed circuit pad. You do not need a big blob of solder at the junction.
With dead bug construction, you will be soldering part leads together, often in the air. After snipping the leads to the required length, put a light coat of solder on the end of each lead to be connected together. This is called "tinning" the lead. Now all you need to do is place the two leads next to each other and heat them again with the tip of the iron and they will stick together. No additional solder should be needed, as some of the solder which is still on the iron tip will flow onto the junction. If the junction is strong enough that a light tug on the parts does not pull then apart, it is strong enough. There is no need to make a strong physical connection between part leads before soldering, such as twisting the leads together, because if you make a wiring mistake and have to fix it, it will be harder to take the connection apart if it is not just held together with solder. Sometimes it is helpful to make a small half loop (hair pin) on the end of a part and lightly compress the loop around another parts lead to hold them together as you solder. This is especially true if the end of one of the parts is not yet secured to something yet.
Part leads should be bent no closer than 1/32" to the body of the part. If you bend the lead right where it comes out of the package, it is likely to break off. This is especially true of transistors and the small Monolithic capacitors. Leads which solder to the copper foil ground plane should have a little foot bent on the end of the leg, about 1/16" is good.
When snipping leads to length, often the cut end will go flying away. Be careful it doesn't fly into your eye or that of an innocent by-stander! This can be avoided by aiming the end of the lead away from you or down towards the work bench.
There are places where you will be using wire to make connections between parts. I use heat stripable magnet wire. This wire has insulation which can be soldered through, if enough heat is used. When tinning heat stripable magenta wire, it helps to have a solder blob on the tip of the iron t help conduct heat into the wire. Or you can scrape or burnt off the insulation with a lighter and cleaned up. You will be needing this wire for winding the toroid coils also. Magnet wire can be obtained from Amidon off the web at a pretty reasonable price for a 1/4 lb spool. You will need #32 and #28 wire. You will also need some toroid cores, which Amidon also sells, so might as well get both the wire and cores at the same time. You can also use a small gauge solid insulated wire, such as wire wrap wire, but this type of wire is less common and harder to find these days. You do not want to use large wire from connecting between parts. Only use large sized wire for connecting the power supply up to the board.
When using magnet wire for connecting to parts or IC leads, first tin the wire to burn through the insulation, then make a small half turn loop on the end. Lightly crimp the loop to the lead to be connected to so the wire doesn't fall off when you solder it in place.
At a minimum, you will need a voltmeter, which in this day and age will likely be a DMM (Digital Multi-meter). An Oscilloscope and frequency counter would be real handy to have, but your not likely to have these if your just starting out. Instead, a simple diode probe can be made to check for RF voltages and a general coverage receiver used to check for the frequency of oscillators. The S meter (if the receiver has one) can also be handy.
This can be made on a little piece of copper clad board or made free air style. If you make the diode probe on a piece of copper clad board, cut little square "islands" in the copper foil for the connection points for the capacitor, resistor and diode on the input (signal) side and the junction of the diode, capacitor and resistor on the DVM side. A straight pin can be used as a probe soldered to the capacitor going the the signal input.
Building the MMR-40:
The diagram below shows the overall layout of the board and the inter-connections between parts. It is mostly drawn to scale, but some parts are drawn larger than the actual size for clarity or to be able to label the part number inside the outline. Like wise, the circuit can be built somewhat more compactly than shown in the diagram. All parts are shown in a horizontal position, but in some places, like when one end of a resistor is connected to the copper ground plane and the other end to a transistor lead, it will make more sense to actually mount the resistor in a more vertical position. Connections to the copper ground plane are shown as red dot and connections which are in the air are shown as blue dots. Wires which connect between parts are shown as blue lines. Some of these wires are shown drawn outside the board outline. You will actually route them near the inside edge of the board. Refer to the schematic to get the part value for each part, as only the part designation label is shown on the diagram.
The schematic and overall layout diagram should be printed out for easy reference. If you try to print directly from your browser, you will likely only print the part of the image which shows up on your screen. To print the whole image, save it to a folder first, then open it with an image veiwing program and print from there. Set your printer preferences to print "scale to page" and print in landscape mode to get the largest picture. You will likely want to save this whole HTML document to your PC, so you don't need to be on line to view it.
The MMR-40 circuits will be built in stages which you can test as you go along if you want. The first stage to be built will be the PTO oscillator, then the audio and control circuit, the receiver section and finally the transmitter sections.
Full layout diagram:
Building the PTO coil assembly:
The PTO is made from a coil wound on a 0.650" long, # 6 nylon threaded spacer. It is supported by two brass nuts soldered to the copper foil of the board. A third nut at the front edge of the board helps eliminate side to side play in the tuning screw. Thread the three nuts onto the screw. Space the rear two nuts so that the nylon spacer fits between them with a little extra "wiggle" room. Space the third nut at the front of the screw about 1/2" from the middle nut. Position the screw/nut assembly on the copper foil about 1" from the front, right side edge of the board, with the first nut just on the copper at the front edge of the board. Hold the assembly to the copper foil with a couple pieces of solid buss wire as shown in the photo below:
Make sure the screw is square to the front edge of the board, and then solder the nuts to the copper foil. You will need some heat for this! After the nuts cool down, remove the wire holding the screw in place.
You will notice four squares of copper isolated from the rest of the board in the above photo. Use a sharp hobby knife to first make a shallow cut to mark the outline of the squares. Then, holding the blade at a slight sideways angle, cut away the copper along the first cut. Then make a third cut on the other side. Repeat as needed to open up an area clear of copper. Use an ohm meter to verify you have removed all the copper between the islands. These four "islands" or pads will be used to mount the L2 coil portion of the PTO circuit. You will need to cut this type of small island pad here and there so that leads of parts which need some mechanical strength but are not connected to the ground plane can be soldered to.
Although not shown on the above photo, the copper foil under where the PTO coil will mount between the last two nuts also needs to be removed. Define the area to be removed by cutting a line into the foil with your knife. Now use your soldering iron the heat up the copper at a corner point. The heat will help de-laminate the copper from the fiberglass board underneath. After a few seconds of heating, work the edge of the foil up with the tip of your knife. Once you roll up the corner a little, you can grab onto it with your needle nose pliers and peal back the foil. Continue adding heat where the copper meets the board or the foil will not come off cleanly in one piece.
Now you can wind the PTO coil on to the Nylon spacer. Make end stop/connection points for the coil wire with a turn of solid buss wire with the two ends twisted together. Position these about 1/4" from the each end of the spacer. See photo of finished coil below.
Thread the screw into the spacer so you have something to hold onto. Snug the spacer up tight to the head of the screw. Now wind 39 turns of # 32 magnet wire onto the spacer. It is easiest to spin the spacer between your fingers and keep some tension on the wire with your other hand as you do. Tin and wrap the starting end of the wire to the wire ring you put on the spacer at the head of the screw end and solder the wire to it. (be quick and use as little heat as possible so as not to melt the wire into the Nylon) As you wind the coil, snug up the turns to each other with the thumb finger nail. Try not to overlap turns. At the end of the required number of turns, (which can be off a few turns one way or the other, so don't worry too much about losing count), wrap the end of t he coil wire around the tab of the wire ring at the bottom of the spacer and solder the coil wire to it.
---The finished PTO coil
Now remove the screw and place the spacer between the rear two nuts soldered to the board. Thread the screw back into the nuts and into the spacer. It is likely you will have to turn the spacer in order to find the spot which will allow the screw to enter the spacer threads smoothly. Do not try to force it, though it should be a little stiff. Once you get it so the screw goes in and out of the spacer with out undo force, secure the back end of the spacer to the end nut with a 1/4", # 6 Nylon screw. If needed, snug the spacer up to the rear nut so that it does not spin when the screw is moved in and out.
A knob for a 1/4" shaft can be added to the screw by first cutting off the head of the screw. A 1/4" or 1/2" long, 1/4" dia threaded # 6 brass spacer can then put on the end of the screw. The end of the spacer can be soldered to the screw to hold it in place. A knob can then be put over the 1/4" dia spacer.
Building the PTO oscillator circuit.
Now comes the nitty gritty of actually wiring up the circuits. We start with the PTO oscillator. The J-310 J-FET and 78L05 regulator are mounted with their legs in the air, the top of the plastic package flush to the board. Bend the leads out as shown, making the right angle bend a little above where the leads come out of the package. If you bend them right where they come out, they will likely break off. The diagram below shows how the parts are connected. For clarity, some of the parts are shown laying down or at an angle, while they should be mounted in a more vertical position as you can just make out in the fuzzy picture of the completed circuit. Connections made to the copper foil ground are shown as a red dot and connections which are floating in the air are shown as a blue dot. Pat values are not shown, only the part number. Refer to the schematic for part values. It is a good idea to use a highlighter to mark off the parts as you put them in place and the connections you make, as to keep track of what has been done and where you stand.The L2 coil is not shown mounted in the diagram, but it will be soldered to the four pad "island" box you cut into the foil. C6 has one lead just floating in the air for now.
Winding the L2 coil:
The L2 coil needs to be wound in a specific way so that the phasing of the oscillator feedback turns come out to the correct pads on the board. If the ends of the feedback winding are reversed, the oscillator will not work. The red T37-2 toroid core is wound with #28 magnet wire. Start by passing the end of the wire up through the hole from the back side of the toroid, as seen as you hold it in one hand. Leave about a 1/2" long pig tail sticking out of the hole. This is the first turn, as a turn is each time the wire passes through the hole in the core.
Now continue winding by passing the long end of the wire down through the hole from the top side of the core, as shown in the diagram below. Wind in a counter clock wise direction. The wire should be wound snug, but not real tight against the sides of the core. Wind 29 turns and then make a small loop about 1" long and continue winding five (5) more turns. This will be the feedback winding. Snip the loop to separate the main winding (S) and the feedback winding (F). Tin the wire ends, leaving about 1/4" lead length from the core. Position the core over the four pad square on the board and solder the main (S) winding to the pads labeled "S". Solder the remaining two wires to the pads labeled "F" and "F1".
Testing the PTO oscillator:
Now that the PTO oscillator has been wired up, we can test it to make sure it works. A 9 volt radio battery can be used to power the oscillator for now. Connect the plus lead (RED) of a 9 V batter clip to the junction of C15 and the "I" lead of the 78L05 regulator. Connect the black lead of the battery clip to the copper foil. Attach the battery to the clip to power up the circuit. First use a volt meter to make sure there is 5 volts (+/- 0.25V) on the output of the regulator U1 (lead labeled "O"). The easiest way to see if the oscillator is working is with an Oscilloscope and to check the frequency with a frequency counter, but you probably don't have either of these. Hopefully you have a general coverage receiver which will tune between 2 and 3 MHz. Using a clip lead or short piece of wire as an antenna and place near one of the coils, you should find a strong signal somewhere between 2.7 and 3 MHz. Exactly where depends on how far the tuning screw is inserted into the PTO coil and if C4 is switched in or out of the circuit. If you can't find a signal, then it is likely you have the S and F windings reversed. The oscillator is probably working, but at a much higher frequency than it should be. Hopefully you didn't make any wiring errors this early in the game, but since your just starting out, it is possible and the wiring double checked. The diode probe connected to the flying end of C6 can also be used to tell if the oscillator is working.
If you do find the signal in the proper frequency range, you can now fine tune the range of the oscillator. With C4 switched out of the circuit and the tuning screw fully inserted into the PTO coil, the frequency should be no higher than 3.000 MHz. This will correspond to 7.000 MHz when the rig is done. The frequency can be fine tuned by moving the turns on L2. Spreading the turns apart will increase the frequency and pushing them closer together will lower the frequency.
Audio and control circuits:
Here is where the circuit starts to become a little more complicated. Start with the U4 op amp near the front left side of the board and add parts to it. Then go over to the U8 op amp and finish with the U3 audio amp. The first part to be mounted will be the IC package. First ground Pin 4 to the copper foil by using a resistor or capacitor lead clipping to make the connection. Tin the copper where the lead will attach. Bend one end of the lead at a right angle and tack it to the copper where you pre-tinned. Then tack solder the lead to the side of Pin 4. This will hold the IC in place. Be very careful to mount the IC the right way. Since it is upside down, you have no way to verify the pin 1 end and once you start adding parts to the pins, it will be difficult to correct if it is not positioned correctly. Now start adding the rest of the parts. For clarity, the position of the parts are not quite where they will ideally end up for a compact assembly, but should give you an idea of where they go. Before mounting V5, cut copper islands from the foil under the un-grounded legs. (Blue dots)
You might want to wire up the mic/key jack now and can be hot glued to the front right corner of the board for now so it stays in place.
Testing the audio and control circuits:
You can test the audio and control circuits using power from the 9 volt battery you used for testing the oscillator. The reason for using a 9 volt battery instead of a more robust power source is that if there is a problem, it is not likely the 9 volt battery will cause any damage.
Before you hook up power to the circuits, connect a small speaker the end of C50 labeled "speaker out" and tack a 1 ufd electrolytic cap between Pin 3 of U3 and Pin 7 of U8, with the + side of the cap to Pin 7 of U8. Now connect up the battery clip, Red + lead to Pin 6 of U3 and the black - lead to ground (the copper foil). Touching the floating end of C42 should result in a very loud buzz in the speaker.
Grounding the junction of R29 and C57 (this is the PTT input) should make the voltage on pin 1 of U8 go from zero (0) volts to near 9 volts. If you touch the end of C42, you should not hear a faint or low volume buzz in the speaker. Grounding pin 5 of U8 should make the voltage on pin 7 go from near 9 volts to zero (0) volts.
If you pass these three tests, your doing very good and can move on. If not, double check your wiring and soldering and keep trying until it works. Before moving on to the next section, connect a wire between pin 6 of U3 to the C15/U1 junction labeled "power" so the PTO will get power after the next section is completed.
Receiver RF sections:
Front of board towards top.
The crystal cans can be soldered to the copper foil to hold them in place. Pre-tin the sides of the round ends of the crystal can and tack these ends to the board. Note that Pin 1 of U6 faces opposite direction of that of U7 and U5. Cut Island pads under ungrounded leads of V1 and C21. Leads of IF transformer T1 can be bend at right angle so they don't touch the copper foil. Make these bends about half way down the length of the pin. Solder the mounting tabs of the IF can to the copper foil. Connect pin 8 of U6 (wire end labeled "TO +5V") to pin 5 of U8. Once the parts shown above have been wired up, wire up the volume control and S1 Wide/Narrow switch and attach the speaker. Make about a 1/4 turn from the factory setting of C21. If you look closely into the hole on top of C21, you will see one end of the screwdriver slot has a slight arrow shape. When the arrow faces the flat side of the package, it is set to minimum capacitance, when it faces the round end, it is at maximum. Do not connect the wire labeled "TO TX KEY" back to Q8 near the front of the board. Instead, ground this connection for now.
The receiver should now be functional. Connect an antenna to the leg of Q2 labeled "TO C27" and you should be able to tune in stations or hear band noise. You can continue to use the 9 volt battery to power the circuits for now. Adjust the slug in the top of T1 for best signal strength. Usually turning it "clock wise" 1/2 to 1 turn will do it.
Start assembly with the T3 and T4 IF transformers. C31 and C35 should be mounted to the transformer leads before you solder the cans to the board. Place the body of the cap flat to the side of the can. This will allow spacing the transformers closer together than what is shown in the diagram. Don't forget to bend the transformer leads out at a right angle, making the bend about 1/2 way down their length. Once the transformer cans have been soldered to the board using the ends of the mounting tabs, tack the C25 cap in place between them.
Cut Island pads into the copper foil to provide a place to mount T4 and T5 as shown by the three box outline. Make real sure these are isolated from the sourounding copper ground plane, as these will have the full DC supply voltage on them. A short here to ground could damage your power supply. After T4 and T5 have been mounted, double check for shorts with your ohm meter. Also cut pads under the un-grounded leads of V3 and V4 (leads with blue dots). Build everything to the right of Q10 and the heatsink. Refer to the overall layout diagram to make the connections shown going off the right edge of the board back to the points they need to connect to near the front of the board.
T4, T5 winding:
T4 and T5 are Bi-filler wound transformers. This means two wires are wound on the core, side by side or lightly twisted together. A total of five (5) turns is used. (remember, a turn is each time the wire(s) pass through the hole in the core. T4 and T5 are wound on a ferrite core (black). Once you have wound the core, you must identify the common ends of each wire and position them so they are opposite each other. Tin or strip the end of the wires and use an ohm meter to identify the common ends of the two wire. Then take one end of each wire which is diagonal from each other and twist these together and solder. This is the center tap of the transformer and produces the correct phasing of the turns. See diagram below: The center tap will connect to the center "island" in the three pad pattern shown in the wiring diagram above.
Use a short piece of wire to ground Pin 5 of U4 (TO MIC JACK) This will put the circuit into CW mode. Clip a clip lead or attach a length of wire to the Junction of R29 and C67 (TO PTT JACK) Grounding this wire when required will put the circuits into transmit mode. Re-connect the speaker to the board. Connect a 12 to 14 volt power supply to Pin 6 of U3 near the front of the board. Make sure you also have a wire connecting from Pin 6 of U3 to the C43/T4 junction pad.
Turn the power supply on. Ground the PTT wire or clip lead. You should hear the 600 Hz side tone in the speaker. Adjusting V5 will change the volume. If you do not hear the side tone, make sure Pin 7 of U4 is near 0 volts and that it is connected back to R37 and R38. Review the wiring of the tone oscillator (Q13 and associated parts) to make sure they are connected correctly. Once you verify the side tone is working correctly, you can disconnect the speaker as listening to the side tone for any length of time can be annoying.
The next step is to peak the transmitter band pass filter, the T2 and T3 IF transformers. For this, you will need the diode probe. Build it now if you have not already done so. The tuning of T2 and T3 should be made near the center of the tuning range of the PTO. Remove the screw from the PTO coil and make sure the band select switch is set to remove C4 from the circuit. Connect the "signal" input end of the probe to the R18/C48 junction. Key the transmitter by grounding the PTT jack lead. Adjust the slugs on the top of T2 and T3 for the maximum amount of voltage as shown on you voltmeter (which is connected to the diode probe). You should not have to turn the slugs much, again like T1, 1/2 to 1 turn clockwise should do it. The adjustment is interactive between the two transformers, so go back and forth a couple of times to find the best peak. You should be able to get a 5 to 7 volt reading on the voltmeter.
Now turn V4 fully counter clock wise. This will turn off the 600 Hz tone to the balanced modulator. The voltage from the diode probe should go to near 0 volts. If it does not, adjust the C21 BFO trimmer slightly until it does.
The final transmitter circuits:
The heat sink has mounting tabs on the bottom. These will solder to the copper to support the heat sink and stand it off the board so that that leads of Q10 can be bent to make the connections to. No insulating washer is needed and a metal screw used to hold the power FET to the heatsink, but be careful not to nick the anodizing on the heat sink, or you could make a short. After you mount the heatsink and Q10, double check with your ohm meter to make sure the metal tab of Q10 is not shorted to ground (the copper foil, as you must know by now!)
L3 is wound with 15 turns of # 28 wire on the red T37-2 toroid core.
L4 is wound with 25 turns of # 28 wire on another red T37-2 core.
Be very careful counting the number of turns. Remember, each time the wire passes through the center of the core, it is counted as a turn. If you are off by just one turn too many or too few, it will drastically affect the amount of output power from the transmitter.
The first thing to do is set the bias current of the PA, Q10. Wire a jumper from the T5/C45/C58 junction over to the T3/C43 junction and connect the positive lead for the power supply to the T5/C45/C58 junction. Solder the negative lead for the power supply to the copper in this same area.
Make sure V4 is still fully counter clockwise or better yet, disconnect C48 from R18 so there is no signal going to Q10. Turn V3 fully counter clock wise. Power up the board, put it in transmit mode by grounding the PTT input. Measure the voltage at the V3/D4/R27 junction. It should measure just over 5 volts. (5.1 to 5.2) If it reads about 0.6 or 0.7 volts, D4 is installed backwards. If it reads much more than 5 volts, you mixed up the zener diode with one of the 1N4148 diodes.
Set your DMM to the 20 amp scale and connect it in series with the positive power supply lead. The red probe will go the plus side of the power supply and the black probe to the positive DC input to the board. There is probably a seperate jack for the red probe on the meter for using the 20 amp current scale of the meter, be sure to move the probe to this jack. It is also a good idea to have a 2 amp fuse in line with the power supply lead.
Turn power onto the board, key the transmitter by grounding the PTT input and note the current being drawn. It will likely be about 190 ma. With the 20 amp scale, the meter will read 0.19 or there abouts. Now turn V3 clockwise until the current goes up by about 10 ma, an increase of one digit on the meter. You will probably find the setting of V3 to be slightly past the mid point of its range. (Which is where it is set from the factory). Be careful when making this adjustment. If you turn V3 up too high, the supply current can go up to as much as the power supply can deliver and that could damage the power supply or Q10. That is why it is a good idea to have a 2 amp fuse in line.
Un-ground the PTT input and remove power from the board. Reconnect C48 if you disconnected it.
You are now nearly done! Only one last thing to do, hook up the antenna jack and check the power output. The center pin of the antenna jack connects to the point labeled "To antenna". If the connection to the jack is less than an inch or two, just run a wire from the center pin to the antenna connection point on the board and another wire to the copper ground foil near that point. If the run is 2 to 6 inches, twist the wires together to the jack. No need for coax for this short a connection.
Connect up a wattmeter and 50 ohm dummy load to the antenna jack. Hopefully you watt meter can read down to 5 watts with reasonable accuracy. You should still have the board configured for CW mode by having the mic input grounded, V4 set fully counter clock wise and the PTO frequency set to mid range. You can remove the DMM from the power supply leads if this is still connected.
Apply power to the board and key the transmitter. At this point, there should be no power output. Turn V4 clock wise and you should start to see power output. Keep turning up V4 untill the power output stops going up. You should see at least 5 watts when it does. The amount of power output can be optimized by "tweaking" the spacing of the wire around the L3 and L4 cores. If you have the wire more or less evenly spaced around the core, try pushing some of the turns closer together on the L3 coil first and see how this changes the power output. If you get more power output, keep moving turns closer together until the power output starts going down again. Then try the same thing with L4. With a 13.8 volt supply, you can get the power output as high as 8 watts with a little fussing with the coils. Also try touching up the tuning of the T2 and T3 transformer slugs to get the most power output.
Power output will vary some with the frequency of the PTO. You should peak up the power output around the frequency you think you will be operating the most often. You probably want to get the most amount of power output in the voice segment of the band, as this I where you want to get the most you can. If the power out is somewhat less at the low end of the CW band it will still be very effective.
Now the board is finished, all tuned up and ready to go! The last thing to do is find a suitable box to put the board in, drill the holes for the jacks, controls, ect and mount the board into it. The D6 diode shown on the schematic but not yet wired to the board should go between your DC power jack and the +DC input to the board for reverse polarity protection. With out this diode, if you hook power up backwards, the board will draw as much current as you supply can deliver until something burns up!
Making a Microphone:
The MMR-40 uses an Electret condenser microphone element. A dynamic mic will not work. Condenser mic elements can be found in a number of consumer electronic products such as cordless phones, answering machines, hands free cell phone mics, computer mics and most anything which uses a mic. They can also be bought new for a dollar or so. A CB mic would be the simplest thing to use, though there are all kinds of possible ways to make a desk mic for the mechanically inventive.
Electret elements are small silver cylinders. There are two connections on the back side of them. Generally, these look like half moons. If you look closely, one of these half moons as a connection leading to the shell of the mic. This is the ground. You can also use your ohm meter to verify this is the pad connected to the shell. Wire the mic element and PTT switch to a 3.5 mm stereo plug as shown below.
Setting the mic gain:
Setting the mic gain can be a little tricky. If set too low, you will have low power output and poor sounding audio. If set too high, your signal will "flat top" and cause splatter, along with poor sounding audio. This is worse than having the audio level too low. The problem with setting the mic gain is your watt meter reads the average power, not the peak power (though some meters have a peak power reading mode). With normal speaking, the watt meter will read about 1/3d of the power produced with CW mode. A louder than normal speaking level "AHHHHH" into the mic will produce a power output of close to the CW power. Say these "AHHHH's" into the mic and turn V1 clockwise until the power output is no longer increasing, typically about 4-5 watts depending on what the CW power output was. Now back off on the setting of V1 just a little.
When using the MMR-40 in CW mode, all you need to do is plug a monaural phone plug into the mic jack. This will ground the mic input and allow the side tone generator to be enabled when keying with the PTT input. You can use either the Wide or Narrow audio filter position, though most of the time you will want to use the narrow setting. When responding to an other stations "CQ", you should try to match the tone of the received signal to the side tone frequency of the MMR-40. This will make your transmit frequency match the other stations. The Narrow filter setting helps in making this tone match, as the filter peak response is the same frequency as the MMR-40 side tone.
All part numbers are for Mouser.com, unless otherwise noted.
Part designator (quanity) value --- Part number
R17, R21, R29, (3) 10 ohms --- 660-CF1/4C100J
R1, R3, R20 (3) 51 ohms --- 660-CF1/4C510J
R9, R12, R18, R37 (4) 100 ohms -- 660-CF1/4C101J
R11, R33 (2) 470 ohms --- 660-CF1/4C471J
R41 (1) 1.5K --- 660-CF1/4C152J
R7a, R7b, R32, R39 (4) 2.2K --- 660-CF1/4C222J
R26, R27, R28, (3) 4.7K --- 660-CF1/4C472J
R4, R10, R14, R19, R25, R36, R38 (7) 10 K --- 660-CF1/4C103J
R5, R6, R13, R15, R22, R23, R31, R35 (8) 22K --- 660-CF1/4C223J
R40 (1) 47K --- 660-CF1/473J
R42 (1) 100K ---- 660-CF1/4C104J
R2, R8, R16, R24, R30, (5) 1 Meg --- 660-CF1/4C105J
V1, V4, V5, V3 (4) 10K trimmer --- 652-3318P-1-103
V2 (1) 50K pannel mount volume --- 313-1500F-50K
C6, C25 (2) 4.7 pfd NPO --- 140-50N2-4R7C-TB-RC
C12, C20, C23, C44 (4) 22 pfd NPO --- 140-50N2-220J-RC
C1, C4, C28, C32, C33, C34, C29 (7) 33 pfd NPO --- 140-50N5-330J-RC
C31, C35 (2) 47 pfd NPO 140-50N5-470J-RC
C8, C47, C51, C53 (4) 330 pfd C0G mono --- 80-C315C331J1G
C52 (1) 680 pfd C0G --- 80-C315C681J1G
C16, C19, C27, C30, C37, C55, C61, C67, C68, (9) .001 ufd disk --- 140-50P2-102K-RC
(25) 0.1 ufd X7R mono--- 80-C320C104K1R (get a few extra of these, just to have around)
C3, C5, C9, C10, C11, C13, C15, C17, C22, C24, C26, C36, C38, C39, C40, C42, C43, C45, C48, C49, C56, C57, C59, C60, C65
C21 (1) 30 pfd trimmer cap --- 659-GKG30015
C63, C66, C69, C70, C72, C73 (6) .022 ufd Film --- 140-PF2A223J
C2, C14, C46, C54, C64 (5) 1.0 ufd 25V --- 140-XRL25V1.0-RC
C50 (1) 47 ufd 16V ---- 140-XRL16V47-RC
C62, C71 (2) 10 ufd 16V --- 140-XRL16V10-RC
C41, C58 (2) 330 ufd 16V ---- 140-XRL16V330-RC
U5, U6 (2) 771-SA612AN/01
U1, U2 (2) 511-L78L05ACZ
U3 (1) 513-NJM#386D
U4, U8 (2) 512-LM358AN
U7 (1) 511-74HC4053N
Q1, Q2, Q3, Q4, Q5, Q11, Q12 (7) 512-2N7000
Q6, Q7, Q9, Q13 (4) 863-2N4401G
Q8 (1) 863-2N4403G
Q10 (1) 512-IRF510A
Q14 (1) 512-J310
D1, D2, D3, D7 (4) 512-1N4148
D4 (1) 512-1N5231B
D6 (1) 863-1N5817G
T1, T2, T3 (3) 10.7 MHz IF transformer --- 42IF222
X1, X2, X3, X4, X5 (5) 10.000 MHz crystals --- 815-AB-10-B2
S1, S2 (2) SPDT slide switch, panel mount --- 629-GS1150511 - get 3 if you want a power on off switch.
(1) 4X6" copper clad board ---- 590-509
(1) 1/4" #6 Nylon screw --- 561-F632.25
(1) #6 Nylon spacer --- 561-L6.625
(1) Heat sink --- 567-637-10ABP
J2 (1) 1/8" stereo jack --- 161-3507-E
J1 (1) panel mount BNC jack --- 571-5227755-2
(1) optional DC power jack 2.5mm pin --- 163-MJ22-EX or 2.1mm pin 163-4304-E
These parts are from Amidon.com
T4, T5 (2) FT37-43 ferrite core
L2, L3, L4 (3) T37-2 Red powdered iron core
(1) 1/4 lb spool of #32 magnet wire, thermalize
(1) 1/4 lb spool of #28 magnet wire, thermalize.
From hardware store or smallparts.com
(3) # 6 brass nuts
(1) # 6, 2" long brass machine screw