This Blog is being REVISED

09 December 2012

[[  Most recent Update 03 September 2013.  ]]

The WT40 blog is currently undergoing a major revision to update the content.  All of the content already posted will remain the same except for minor editorial updates.

There will be NO NEW CONTENT posted to this blog until revisions are completed.

For those who may have begun building the WT40 Transceiver, I will be happy to answer specific questions via email.  My email address:  w6bky1(at)gmail(dot)com

Please accept my apology for any inconvenience this may cause.

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WT40 AUDIO RESISTANCE MEASUREMENTS

AUDIO RESISTANCE MEASUREMENTS . . .

. . . to verify that components are correctly connected and properly soldered in place.

[[  Most recent update:  27 October 2012.  ]]

PREPARATION

IMPORTANT: Resistance measurements are to be taken BEFORE jumpers are installed – OR – with only one end of each jumper connected, as shown below.

Before doing resistance measurements, connect the two test leads on your DMM together and record whatever value you get with your meter set to its lowest resistance scale. This is the “Zero” Ohms value for your meter.

Your DMM may actually show zero ohms with test leads shorted together.

On meters I have used, shorted test leads show somewhere between 0.2 to 0.5 Ohm. Some meters have provisions for adjustment so that the meter will read zero for a dead short.

Unless specified otherwise, resistance measurements are taken from the POINT INDICATED to the GROUND.

Resistance values are specified in Ohms; k = X 1,000

Resistance Measurements (other than ZERO and OPEN, which should be “right on”) are OK if they are within plus or minus 15%. If measurements are off more than 20%, you have one or more wiring errors.

The readings shown below were taken using a EXTECH EX570 DMM, and have been rounded to the nearest value.

MEASUREMENTS TO GROUND

[] TP40 to Ground Buss . . . . Zero

NOTE: Now that you have verified that TP40 is connected to the Ground Buss, it can be used as your GROUND POINT for Resistance Measurements.

[] TP26 . . . . . . . . . . . Zero
[] TP27 . . . . . . . . . . . Open, No Continuity
[] TP28 . . . . . . . . . . . Open, No Continuity
[] TP29 . . . . . . . . . . . Zero
[] TP30 . . . . . . . . . . . No Measurement at this time
[] TP31 . . . . . . . . . . . Open, No Continuity
[] TP32 . . . . . . . . . . . Open, No Continuity
[] TP33 . . . . . . . . . . . Open, No Continuity
[] TP34 . . . . . . . . . . . Open, No Continuity
[] TP35 . . . . . . . . . . . Open, No Continuity
[] TP36 . . . . . . . . . . . Zero
[] TP37 . . . . . . . . . . . Open, No Continuity
[] TP39 . . . . . . . . . . . Zero

You have probably noticed on the Layout Drawing that TP28, which is the Entry Point into the Audio Amplifier module, does not connect to anything on the circuit board. This may seem rather strange at first glance, but a quick inspection of the Schematic Diagram shows what is going on. Before the signal enters the circuit board it passes through R17, the Audio Gain potentiometer, which will be mounted on the Control Panel of the Transceiver. (More about mounting potentiometers when we get to Building the Control Panel.)

TP28 provides a place to connect the signal wire from the Product Detector to the signal wire going to R17.

It is helpful to use color-coding for the signal wires, as illustrated in the photo below.

Rotary potentiometers are manufactured so that as the shaft is turned in a ClockWise direction, the wiper moves from the upper terminal (Green wire to TP26) in this photo toward the lower terminal in this photo (Orange wire to TP28). The Wiper terminal is in the middle (Yellow wire to TP27). The upper terminal in this photo (Green wire to TP26) would be connected to the Ground Buss via TP26. The colors used are arbitrary. More detail about this when we get to Current & Voltage Measurements and Initial Operational Test.

The photo also illustrates the use of heat-shrink tubing, which I added after cleaning the contacts. The heat-shrink tubing provides insulation on soldered joints, and strengthens the connection.

FYI: The potentiometer pictured here was salvaged from surplus military electronic gear.

R17 will not be connected into the circuit until we get to Operational Testing, but it does no harm to plan ahead.

Measurements on transistors are from the leg indicated to Ground.

Q5, 2N3904
[] Emitter . . . . . . . . . . . 220 Ohms
[] Base . . . . . . . . . . . 8.6k
[] Collector . . . . . . . . Open, No Continuity

Q6, 2N3053
[] Emitter . . . . . . . . . . . 148 Ohms
[] Base . . . . . . . . . . . Open, No Continuity
[] Collector . . . . . . . . . Open, No Continuity

POINT to POINT MEASUREMENTS

The three measurements, immediately below, are between two test points, NOT to Ground.

[] TP30 to TP32 . . . . . . 2.2k
[] TP30 to Q6 Collector . . . . . . Open, No Continuity
[] TP30 to Q6 Base . . . . . . Open, No Continuity

Correct any errors found during Resistance Measurements before proceeding to Current & Voltage Measurements and initial Operational Test.

- END of initial resistance measurements. -

 

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WT40: POPULATING the AUDIO AMPLIFIER CIRCUIT BOARD


[[ Most recent Update to this page - 27 October 2012. ]]

THIS BLOG ENTRY CONTAINS:

[] Introduction (You are here.)

[] Audio Amplifier Module Parts List

[] Preparing the 2N3053 Transistor

[] Preparing the Circuit Board

[] Tie Points

[] Jumpers

[] Initial Check-Out

Building of the WT40 Transceiver will begin with the Audio Amplifier module and proceed “backward” through the modules until we get to the antenna connection.


For just about everything you do in electronics there are at least two ways to do it; sometimes there are dozens of ways to accomplish the same thing. This means choices must be made. For the purpose at hand, I have made some of those choices for you. I have chosen to use discrete components for the Audio Amplifier because I think discrete components are easier to work with.

Begin the building process by collecting all the parts.

WT40 AUDIO AMPLIFIER MODULE PARTS LIST

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Resistors
1/4 Watt, plus or minus 5% tolerance.
Values shown in Ohms; k = x 1000.

[] One: 10
[] One; 150
[] One: 220
[] One: 1k
[] One: 2.2k
[] One: 4.7k
[] One: 10k
[] One: 22k
[] Two: 47k

Quarter Watt resistors can be purchased for a penny each, or less, from parts suppliers such as JAMECO and MOUSER, – BUT – to get such a good price, they must be purchased in lots of 100, or more pieces. For small projects, such as the WT40 Transceiver, it is probably less expensive to pay the “extra” few cents to purchase them in smaller quantities.

Alert readers, such as yourself, will have noticed that the 47k resistor on the far right in the photo is physically larger that the others. That’s because I didn’t happen to have a 47k quarter watt resistor on hand at the time I was taking the picture, so I substituted a half watt. The physical size has nothing to do with the resistance value.

Experienced builders will probably have noticed that the resistors in the photo line up, left-to-right, according to value, 10 Ohms on the left, and progressing to the 47k resistor on the right.

Audio Gain Control
Plus or minus 20% tolerance, 1/4 Watt, Audio Taper Potentiometer (logarithmic).

[] One: 10k, JAMECO # 255426, or equivalent.

NOTE: The Audio Gain potentiometer mounts on the Control Panel, NOT on the circuit board, but you might as well add it to your parts collection now because you will need it during check-out of the Audio Module.

You may be wondering . . . What about a knob for the potentiometer? That’s a good question. Actually, no knob is needed at this point in the game because the shaft is easily turned without a knob. Knobs and switches will be detailed when we get to the Front Panel, much later in this series. You can, of course, get a knob now – just be sure it will fit the shaft on the potentiometer you choose for Audio Gain control (the shafts come in different diameters, and some are slotted or half-moon shaped).

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Capacitors
Plus or minus 20% tolerance, Monolithic Ceramic, Type Z5U, or equivalent.

[] Three: 0.1 uF

Polarized Electrolytic Capacitors

Plus or minus 20% tolerance, Radial -Lead, rated for 16 volts or more.

[] Three: 10uF
[] One: 47 uF
[] One: 220 uF

NOTE: Electrolytic capacitors of a given capacitive and voltage rating come in different physical sizes. I suggest you obtain the smallest size available from your parts supplier (Excluding surface – mount capacitors, which is story for another day).

Miscellaneous Parts

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[] One: Radio Shack #276-148 Dual Circuit Board, or equivalent .

[] Mounting Hardware for the circuit board. The exact hardware for mounting the modules will depend upon how the builder (YOU) decide to package your transceiver. At this point in the building process, the main purpose for the standoffs is to provide an Anchor at each corner of the circuit board for the Ground Buss. The standoffs listed here can be useful during final assembly of the transceiver, no matter what packaging procedure is used.

[] Four: 1/4 inch, Hex 6-32 threaded, male/Female standoff, 1/4 inch long, JAMECO #133542, or equivalent.
[] Four: 3/4 inch, Hex 6-32 threaded, Female/Female standoff, 5/8 inch long JAMECO #77623, or equivalent.

[] One: Heat Sink for the 2N3053 transistor, MOUSER part number 532-323005800, or equivalent.

The heat sink fits snuggly on the transistor, and will require quite a bit of pressure to mount it. Take care not to damage either the heat sink or the transistor when mounting the heat sink.

The transistor and heat sink should look something like the photo, below, after mounting the heat sink.

Notice that the legs of the transistor have been formed for inserting onto the circuit board before the heat sink was mounted.

Most any heat sink for a TO39 transistor will do the trick. “TO39″ simply means “Transistor Outline number 39″, referring to a line drawing that shows the outline of the transistor. The 2N3904 transistor used for the preamplifier is a TO92, and needs NO heat sink.

You can fabricate a heat sink adequate for this application using #20 or #22 bare copper wire, as shown in the photo, below.

A wire heat sink requires the transistor to have a metal case so the heat sink can be soldered to the case.

Making a heat sink this way uses about six inches of wire, and is a rather labor intensive task, which requires a bit of practice to get the wire shaped “just right”, so it is not a job to be taken lightly.

Back to the parts list . . .

[] About 19 inches: #22 bare copper wire for the Ground Buss and Tie Points. (And another six inches, or so, if you plan to make your own heat sink.)

NOTE: You will use about 12 feet of #22 bare copper wire for Ground Buss and Tie Points if you build all the modules in this transceiver following the procedure outlined here.

[] About 6 inches: #24 or #26 Stranded Hook-Up Wire for Jumpers.

Speaking of Jumpers, if you don’t already have them, it would be a good idea to get set of test / jumper cables with clips on each end, Radio Shack # 278-1156, or equivalent. these can be very useful during testing modules.

[] About a foot, or so, of 3-wire hook up cable (sometimes called “intercom cable”) to connect the Audio Gain potentiometer to the Audio Amplifier module during testing. I use salvaged, multi-color ribbon cable for this sort of thing because wire of any kind is usually sold by the pound and/or in spools of 100 ft or more, which is a lot of wire, and it would take a couple of lifetimes to use up a 100 ft spool of of #24 or #26 hook-up wire (unless you plan to do an awful lot of wiring). You may be able to buy wire by the foot at your local electronic parts outlet, and some Radio Shack stores still stock wire to sell by the foot – – ask for the 3-conductor intercom wire, #278-871.

This intercom wire cable may (or may not) be available at your friendly, neighborhood Radio shack store. There are several Radio Shack stores in the area where I live, and I have found that some stores carry a larger variety of items than others.

NOTE: 3-wire intercom cable, or equivalent, will also be need for testing of the Product Detector and VFO modules. This cable comes in handy for all sorts of things at the workbench, so you might as well stock a few “extra” feet for future use. “Equivalent” cable can be easily fabricated using three different colors of insulated hook-up wire twisted together.

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An assembled and tested Audio Amplifier module shown in the photo, below.

The red jumper wires on the circuit board are for distributing 12 volts to power various parts of the board. 12 volt power enters the circuit board at TP30, near the upper right-hand corner of the board in this photo.

The blue wire is a jumper to carry the signal from the Collector of the 2N3904 preamplifier Base of the 2N3053 Amplifier transistor.

Experienced builders may what to use a different layout, such as the one shown below, so that multiple modules can be placed on a single dual circuit board, RS #276-148, or equivalent.

This compact layout is electronically identical to the one shown earlier, and leaves half the board to be used for another module, perhaps the Product Detector and/or the Audio Buffer.

PREPARING THE 2N3053 TRANSISTOR

The “legs” on the 2N3053 transistor are pre-formed before the heat sink is mounted, as shown in the photos, below.

Notice in the photo that the collector leg is attached to the case. This means that there will be 12 volts present on the case whenever power is applied to the circuit board, and neither the case nor the heat sink can be touching any other component.

In the photo, below, notice that the 2N3053 stands about 3/16 of an inch above the surface of the circuit board.

Resistors and capacitors mount snugglyt against the circuit board.

More about this when we start POPULATING the circuit board.

A simplified diagram of the Audio Amplifier module is shown below.

This is a generic module with Power, Input Signal (from the Product Detector module), Output Signal (to Headphones and/or an OPTIONAL Speaker), and, of course, a GROUND connection – the connection that all modules must have.

The Audio Amplifier is more than adequate for headphone use, but is not suitable for direct connection to a speaker.  Yes, it will drive a small speaker directly, but the performance will be marginal, at best. A separate, amplified speaker unit, such as the ones pictured below, is recommended if you want room-filling sound.

The SONY speaker shown in the photo, was once part of a computer audio system. Similar units can sometimes be purchased in “thrift” stores for a couple of bucks (that’s where I got this one).

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This Sony unit measures about 6 3/4 inches tall by 2 3/4 inches wide by 4 3/4 inches deep. The unit is powered by either four “c” cells, or a 6 VDC “wall wart”. This is a nice little speaker unit, and I have used it several years, both on my workbench and as part of my Ham radio station.

Or – – you can build such a device to drive an external speaker, such as the one in the photo below. (More about this when we get to Optional Features.)

The home-brew amplified speaker shown was build (almost) entirely from junk box parts. For scale, the speaker is about 2 1/2 inches in diameter, and was salvaged from a discarded CB radio that I purchased at a thrift store. I purchased the “box to put it in” at the same thrift store for $ 0.25. Yep, for a quarter, I got a fine little box to house an auxiliary amplified speaker.

( “Thrift” stores are one of my favorite sources for parts ! )

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Be that as it may, I used this junk box speaker unit with an earlier version of the transceiver. This home-brew amplified speaker is now retired, and sits on a shelf along with other “retired” equipment I have built.

PREPARING THE CIRCUIT BOARD

As mentioned briefly in previous posts, once all the required parts are on hand, the next task is to prepare the 276-148 circuit board. The procedure shown here assumes that the Radio Shack #276-148 Dual Printed Circuit Board, or equivalent, is being used as the platform on which the modules will be built.

Notice the orientation of the circuit board – – the half on the left end contains 213 perforations for mounting components; the half on the right end contains 228 perforations. This is the orientation shown in the layout drawings and photos of the Audio Amplifier board.

FIRST, Mount Standoffs at each corner of the Radio Shack #276-148 Dual Circuit Board, or equivalent.

At this point in the process the standoffs will be serving as anchors at each corner for mounting the Ground Buss, which you can see looping around the standoffs in the photo, above. The recommended standoffs are:

[] 1/4 inch long Hex 6-32 Threaded Male / Female standoffs, JAMECO #133542, or equivalent, on the Solder Side of the circuit board.

[] 3/4 inch long Hex 6-32 Threaded Female / Female standoffs, JAMECO #77552, or equivalent, on the Component Side of the circuit board.

Much later in the building process, when the circuit boards are mounted in their final configuration, the standoffs can be easily removed and replaced with different length standoffs, if required to accommodate the needs of the configuration.

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ADD THE GROUND BUSS

When the standoffs are in place, ADD THE GROUND BUSS, using about 11 1/2 inches of #22 bare copper wire.
As you can see in the photo, the Ground buss loops around the entire circuit board.

At each corner, the Ground Buss passes through a perforation, goes around the standoff, then passes through another perforation back to the solder side of the board, then continues around the entire board in a similar manner.

Where the two ends of the Ground Buss meet, there should be about 3/8 inch overlap where the two ends are soldered together.

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TIE POINTS

Each circuit board will have several TIE POINTS. These are labeled TPx in the layout drawing, shone below. The number “x” is for identification. The points are added, as needed, as you mount components onto the circuit board.

Tie points serve three functions:

[] Connecting points between modules

[] Test points for module check-out
[] Terminus for jumpers within a circuit board. TPs for jumpers are, sometimes, simply a perforation in the circuit board through which a wire is passed and soldered to a component.

Tie points are shown on Layout Drawing in two forms:

[1] Bold black lines between two adjacent perforations . . .

[2] Gray circles around a single perforation . . .


The gray circles simply show where to insert one end of a Jumper Wire through a perforation.

The bold black lines between two adjacent perforations in the Layout Drawing represent a loop of #22 bare copper wire that has been fashioned into a Tie Point, as illustrated below.

A wire loop type Tie Point requires about 2 inches of #22 bare copper wire folding it into a “u” shape so it can be inserted into two adjacent perforations.

Twist the wire on both the component side and the solder side, as illustrated in the drawing, above.

NOTE: It is important that the bare copper wire if free of corrosion so that the solder adheres tightly to the wire. If there is any discoloration to the wire, clean it with very fine sandpaper, steel wool, or other fine-grained abrasive material.

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Form the wire to make a “U”. I find it best to form the “U” before cutting the Tie Point from the end of the wire.
Cut the wire to get a long, skinny, upside-down “U”.

The photo, below, shows a newly formed “U” that has been inserted into the circuit board to become a Tie Point for connecting to Ground, such as TP39 on the Audio Amplifier module. Tie Points that are Ground Connections, such as TP39, are placed in the perforations nearest to an edge of the circuit board.

The photo, below, shows the twists on both surfaces of the circuit board. These twists hold the tie point firmly in place.

There will be a bit is “excess’ wire on the solder side of the circuit board. Since this particular Tie Point is for a Ground connection, form about 1/4 inch of the two “legs” along the ground buss before soldering.

NOTE: If the Tie Point is NOT going to be soldered to the Ground Buss, it is best to leave the excess wire in place until after all the components being connected to the Tie Point are connected and soldered, then trim the excess.

The photo below shows a Ground Tie Point soldered to the ground buss.

Allow about 30 seconds, or so, for  the solder to cool, then solder the Tie Point on the component side of the circuit board.

Notice in the photo, below, that the loop portion of the Tie Point is covered with solder.

Tie Points that are NOT connected to ground, such as TP38, are placed so there is one or more perforations between them and the ground buss.

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JUMPERS

Jumpers, shown clearly on the Schematic, are omitted from the Layout Drawings because they tend to clutter the drawings.

Wire Jumpers are used to distribute signal and/or power to various parts of the circuit board.

INSTALL JUMPERS LAST, immediately before Resistance Measurements, as will be explained later, when we get to doing testing the circuit board.
INSTALLING  COMPONENTS  on  the  CIRCUIT  BOARD

Notice, on the Layout Drawing, that the OUTPUT SIGNAL tie point (TP38) is located TWO perforations away from the Ground Buss.

The GROUND tie point (TP39) is placed in the last perforation on the board and soldered directly to the Ground Buss.

The order in which the components (other than jumpers) are placed on the circuit board is a matter of personal preference. I started by placing the 2N3053 and its attached Heat Sink onto the circuit board, then added the other components and tie points.

Another approach which I have used successfully is to start by fabricating all the wire Tie Points, then adding the other components; transistors, resistors, capacitors, etc. The point being, use whatever approach to populating the circuit board that makes sense to YOU.

- – BUT – -

* * * * INSTALL JUMPERS LAST, as explained in detail, later. * * * *
PREPARING THE 2N3053 TRANSISTOR

The 2N3053 is an NPN Bipolar transistor housed in a TO39 metal case with three “legs” that allow connection to the Emitter, Base, and Collector; left to right in the photo, below.

Notice in the photo, below, that the Collector leg is connected directly to the CASE housing the transistor.


This is IMPORTANT because it means that voltage is present on the case when voltage is applied to the circuit, and the case and the heat sink must not touch any other component on the board.

Form the legs so that the 2N3053 will stand about 3/16 inch above the circuit board, as shown in the photo, below.

After the legs are formed properly, attach the Heat Sink before inserting the transistor into the circuit board.

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The Layout Drawing, below, shows the position of the perforation where the Emitter leg of Q6 is inserted through the circuit board.

The leg from the Emitter is inserted into the perforation 8 perforations from the right end of the board and 7 perforations up from the bottom.

Shown below is a top view of Q6,the 2N3053 transistor, mounted on the circuit board – – with the Heat Sink Removed – – to indicate where the legs pass through to the Solder Side of the circuit board, where the Base leg is soldered to the jumper wire coming from the Collector of Q5, the 2N3904 transistor. This solder joint is designated TP34 on the Schematic and Layout Drawings.


This photo was taken after one end of Jumper 6 (the blue wire) had been soldered in place at TP34.

It is important that JUMPERS be INSTALLED LAST, as will be explained in detail, later.
Components can be added to the circuit board in any order you wish. I recommend installing and soldering C36 from the Emitter of Q6 to TP38 next in order to hold Q6 firmly in place.

Be sure to orient C36 with the POSITIVE side connected to the Emitter of Q6.

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NOTE: Not all electrolytic capacitors are polarized, but the ones use in the Audio Amplifier module ARE POLARIZED. It seems a bit strange that the positive connection of a polarized capacitor is indicated on schematic drawings while the negative connection is indicated on the body of the capacitor. – – Just one of the strange little quirks of “standardized” notation used in electronics.
On the Solder Side of the circuit board, pictured below, the leads from components are formed firmly against the board with about 3/16 inch overlap, excess wire trimmed, then soldered.

The other connection to Q6 that will help hold it in place is C35, the 47 uF electrolytic capacitor that goes from the Collector to the Ground Buss, with the positive side of the capacitor to the Collector.

NOTICE, in the layout drawing, that the wire from the Negative side of C35 will pass under the 22k resistor R24 on the Solder Side of the board on its way to the Ground Buss.

Proceed to populate the remainder of the circuit board however you wish. Take your time and double check all connections before applying solder. Correcting wiring errors is sometimes necessary, but it is not much fun.

The photo, below, shows tha Solder Side of the completed Audio Amplifier circuit board.

NOW it is time to connect the JUMPER wires — BUT — solder ONLY ONE END, as shown in the photo, below.

Why connect only one end? (You might want to know.) Because we have not yet done Current, Resistance, and Voltage Measurements, which will be done in WT40 Audio Tests and Measurements.

The “loose” end of the jumpers will be used as Test Points for Tests and Measurements, then soldered in place when testing is completed.

Use insulated hookup wire for the jumpers. The color is arbitrary, but I always use red wire to carry 12 volt power, and some other color for signal connections.

If you are following the layout I have used, Jumper 4 from TP30 to TP37 is about 3 1/2 inches; Jumper 5 from TP31 to TP32 is about 2 inches; and Jumper 6 from TP33 to TP34 is about 1 3/4 inch. The lengths are not critical, but must reach from one point to another with little or no excess.

NOTE: If you are using stranded hook-up wire (which I recommend), about 1/4 inch of insulation mustt be stripped from each end and covered with solder BEFORE placing them on the circuit board. Twist the stranded wire tightly together on each end of the jumpers before applying older.

After all components have been soldered in place, it is time take a break and relax for a while in preparation for . . .

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INITIAL CHECK-OUT

First, a Few Words Regarding Testing:

Each module will be tested to make sure it is functioning properly before being connected to other modules for operational testing.

A generic test procedure is outlined below.

[] Visual Check to make sure all the components are present and properly soldered into place.

[] Resistance Check will reveal “short” circuits and “open” circuits.

[] Current Check to be sure excessive current is not being drawn, or that no current is being drawn in a circuit that should be drawing current.

[] DC Voltage Check to be sure the proper voltages are present at key points in the circuit.

[] AC voltage checking for signal processing modules.

( Of course, a passive module, such as the receiver 40 meter Filter, does not require testing for current and voltage. )

[] Operational check to verify the module if functioning properly.
The most likely cause of problems on a newly built circuit is a WIRING ERROR of one kind or another.

WIRING ERRORS include:
[] Missing components
[] Components not connected
[] Components connected to the wrong place
[] Connections not soldered
[] “Cold” solder connections
– insulation material, such as enamel, not removed before soldering
– not enough heat applied to flow the solder
– mechanical shock or movement before the solder solidifies
[] Solder “bridges” causing a “short” circuit between solder joints.

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VISUAL INSPECTION

Begin your check-out with a thorough VISUAL INSPECTION to make sure that there are no missing parts, and that everything is connected correctly and properly soldered. Defects will, of course, become obvious during resistance, current and/or voltage checks, but a good visual check can often spot errors that can be quickly and easily corrected before electronic testing begins and, thus, save a lot of time.

Begin your Visual Inspection with a COMPONENT COUNT.

[] On the Component Side of the circuit board, you should find:

[] Three Jumper Wires CONNECTED AT ONLY ONE END. (The unconnected end of the jumpers will be used as test points during Resistance Measurements and during Current Measurements.
[] Two Transistors, a 2N3904 and a 2N3053. The 2N3053 should have a heat sink attached.
[] Ten 1/4 Watt resistors.
[] Three 0.1 ceramic capacitors.
[] One 1N4148 diode.
[] Three 10 uF electrolytic capacitors.
[] One 47 uF electrolytic capacitor.
[] One 220 uF electrolytic capacitor.

If you find a discrepancy in component count, use the layout diagram and/or the schematic to find the error.

[] On the Solder Side of the circuit board, check to see that all components are correctly connected and properly soldered. I use a magnifying glass for this check because I have found that magnification sometimes shows problems that I would miss with the naked eye. Finding a wiring error or a bad solder joint with a visual check is a heck of a lot easier than tracking it down during resistance, current, or voltage checks.

Correct any errors found during the visual inspection before proceeding to WT40 AUDIO TESTS and MEASUREMENTS.

- END of WT40 POPULATING the CIRCUIT BOARD -

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WT40 PACKAGING

[[  Most recent Update:  27 October 2012.  ]]

WT40: PACKAGING

After you have built a few electronic projects, you may wonder why they are called electronic instead of mechanical.

By mechanical, I mean such things as:

[] front & rear panel layout
[] placement of parts on the circuit boards
[] arranging circuit boards on the chassis
[] a box to put it in
[] cables and connectors
[] etc.

I have built some items that look pretty good, but most of my home brew projects are built by simply wiring the circuits without much thought or effort toward appearance. I even use ugly (point-to-point) wiring technique as opposed to printed circuit (PC) boards. If I were in the business of building stuff in great numbers to sell, I would, of course, use PC boards and assembly line techniques. Yes, I have made some PC boards, but for me they are more trouble than they are worth for one-of-a-kind projects.

Packaging is important, particularly if you are planning to use your home-brew equipment for many months or years, and it’s none too early for you to start thinking about what you want your 40 meter transceiver to look like when you have finished it. Whenever possible and/or practical, I will present alternative approaches for packaging.

Three packaging methods I have used successfully are briefly outlined, below.

[1] Build on a single, relatively large circuit board, then put it in a suitably sized box.

[2] Build on two boards, one for the receiver section and one for the transmitter section, then put them into a suitably sized box or into separate boxes.

[3] Build and test each of the many module separately, then hook them together so they fit into a box or boxes, then connect the boxes together.

Building technique number [3] is the method that will be presented here, using three boxes:
[] Control Head, contains the Control Panel, plus VFO and VFO buffer.
[] Receiver, contains all receiver circuitry, except the VFO.
[] Transmitter, contains all transmitter circuitry, except the VFO. The transmitter box also houses the antenna switching circuitry.

The builder (YOU) are, of course, free to use any method you choose. That’s one advantage of building your own equipment – you can, within certain limits, package it any way you want.

Before we start building, perhaps it would be a good idea to take a quick look at what all this is leading to.

The simplified functional diagram below shows the contents of the RECEIVER section of the WT40 transceiver .


Some things to notice in the diagram:

[] Only the units pertaining to the Receiver are shown.

[] The Audio Amplifier module is contained within the dotted-line enclosure.

[] The VFO is used to determine the frequency of both the Receiver section and the Transmitter section of the Transceiver.

[] the VFO is tuned with a Potentiometer, as opposed to the traditional variable capacitor.

[] The transmit / receive (T / R) switching is done by relay. Yes, there are more elegant and clever ways to do T / R switching, but they are usually employed to implement break-in keying and/or to achieve minimum physical size for the unit. Neither minimum size nor break-in keying were high priority for this transceiver.

THE PLAN

First, we will build the Receiver section, including the VFO because the receiver can not function without a VFO. When all the modules in the receiver have been built and tested individually, the receiver modules, along with the VFO and VFO buffer, will be assembled and tested.

Next, the Transmitter modules will be built, tested and assembled.

Finally, the whole transceiver will be assembled and tested to verify it is working properly.

There is much work to be done, but first . . .

A FEW WORDS REGARDING RADIO RECEIVERS

We are bathed in electromagnetic radiation (radio signals) 24 hours each day. There is no escape. Some of this radiation is useful, most is not. That which is not useful is, by definition, “noise”.

A radio receiver has two primary functions:

[1] The radio receiver must have enough Sensitivity to be able to detect the electromagnetic signal of interest to the user.

[2] The radio receiver must have enough Selectivity to be able to eliminate most, if not all noise, and present only the signal of interest to the user.

For the WT40, the signal of interest is in the Ham radio 40 meter band.

There are many auxiliary functions performed inside a radio receiver, but unless the receiver has good sensitivity and selectivity, the other functions are of little or no use.

SELECTIVITY is accomplished by good circuit design in general, and good filtering in particular.

SENSITIVITY is accomplished with amplification circuits of various kinds.

NOTE: The Antenna contributes to both sensitivity and selectivity, and will be addressed after the WT40 is assembled and tested.

In order for a receiver to be useful for Ham Radio communications, it should be sensitive enough to detect very weak signals. Most communications receivers, including receivers built for the Ham bands, are capable of detecting signals of less than one micro-volt (uV). That’s 0.000001 volt, and that’s a pretty small amount of voltage. It is so small that it can’t be detected with ordinary test equipment such as your DMM. Having said that, I should point out that there are Ham Radio signals “on the air” that will present 5 to 50 microvolts (uV), or more, at the antenna input on your receiver.

SELECTIVITY is accomplished with with good circuit design in general, and good filtering in particular. The receiver section of the WT40 has two types of filters:

[1] A radio frequency filter that attenuates all signals except the 40 meter signals, such as the one pictured below.

[2] An (optional) audio frequency filter is designed specifically for receiving CW (Morse Code) signals.

In order for a receiver to be useful for Ham radio communications, it should be selective enough to eliminate most of the “noise” that comes into the receiver. This is particularly important in receivers used for communications because the signals are usually much weaker than those of commercial broadcasts, and are usually packed much closer together.

It is good to have as much filtering as possible at the “front end” of the receiver – the first circuits encountered by the signal of interest when it enters the receiver. This will eliminate much of the “noise” before it gets into the following circuits and causes trouble. The receiver 40 meter filter shown above does this for the WT40.

The signal-to-noise relationship is more complex than the simple explanation presented above would indicate. For example, if the signal of interest is 10 uV and the noise is 20 uV, the signal will be obliterated by the noise. Not only that, but there is a certain amount of noise generated within your radio by the components simply doing their job. All those electrons rushing hither and yon can create quite an uproar!

Be that as it may, sensitivity and selectivity work hand-in-hand to grab the signal of interest from “thin air” and process it in such a way as to make it clear enough and strong enough for you to hear.

Magic!

The Schematic Diagram, below, shows virtually all the circuitry for the WT40 Receiver section.

OMITTED circuitry includes Antenna Switching, Voltage Regulation & Distribution, and the Variable Frequency Oscillator (VFO).
The schematic diagram shown above may appear a bit overwhelming to the inexperienced builder. Notice, along the bottom of the schematic, that the circuit is divided into SIX modules:

[] Receiver Filter
[] Radio Frequency (RF) Amplifier & Mixer
[] Audio Buffer
[] Audio Preamplifier
[] Audio Amplifier

Notice, also, the TWO OPTIONAL units: 1) An Audio Filter and 2) A Speaker. More about options after we have completed the non-optional modules.

Each module will be built and tested, then the modules will be assembled and tested as a complete receiver.

For the benefit of inexperienced builders, much detail will be presented for building the Audio Amplifier Module because this is the first module in to be built in this series. It is not my intention to insult anyone’s intelligence by dwelling on boring details, and I think it is equally important to present enough information so the inexperienced builder does not get lost in the process.

Subsequent modules will omit some of the detail.

For the subject at hand, which is building the Audio Preamplifier & Amplifier modules, a Schematic for the Audio Amplifier Module, which includes both Preamplifier and Amplifier circuits, is shown below.

Incoming signals will be carried by a twisted pair (or by miniature coaxial cable such as RG174 or equivalent, if you prefer). Notice on the Schematic Drawing that signal entry points, such as the one for Audio In, require TWO Tie Points: one for the signal (TP28) and a companion Ground connection (TP29).

The Layout Drawing shown below is one of many that work equally well. I think this one is well suited for the inexperienced builder.

A photo of a finished Audio Amplifier module is shown below.

Why build the Audio Module first? (you might want to know).

Because that is where “the rubber meets the road”, so to speak, or more exactly, the Audio Amplifier module creates the electrical signal that drives the earphones or speaker. Your ear is, after all, the final arbiter of the quality of the radio receiver.

Also, and more importantly, the Audio Module contains many of the types of components that are used throughout the transceiver. After building and testing the Audio Module, the inexperienced builder will be ready for learning about more advanced building techniques, such as coil winding.

Coil winding?!

Yes, you will be winding a few coils for use on some of the modules. No, this is not simply to make life difficult for you – some of the inductors (coils) that are required for the transceiver are not off-the-shelf components. Not to worry – after you have wound a couple of coils, the task will be a “piece of cake”; I promise!

FYI:  You can see some of the coils you will be winding in the photo of the Receiver Filter shown earlier in this post.

Next time, in WT40: AUDIO MODULE, AN INTRODUCTION, we’ll take a Parts List along with some information about preparing and populating the circuit board.

- END OF WT40: PACKAGING -

 

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WT40 TOOLS, SUPPLIES, and PARTS

[[  Most recent Update:  20 November 2012.  ]]

TOOLS

If you are going to build stuff, you will, of course, need some tools. Chances are, if you are reading this, you already have most of the tools you need to get started building. If not, the Construction Techniques chapter in the ARRL Handbook does a good job of showing what you need. Actually, the ARRL Handbook is one of the most useful tools you can have, so consider it to be “tool number one” on your list. You can sometimes find used Handbooks, on the “freebie” table at your local Ham Club meeting. I’ve seen them in used bookstores for five to ten bucks. Even if you pay the new price, whatever that is these days, the Handbook is worth every penny.

You don’t need all the items mentioned in the Handbook in order to get started. I think a minimum list should include:

[] ARRL Handbook (tool number ONE)
[] Long Nose Pliers
[] Duck Bill Pliers
[] Diagonal Wire Cutter (commonly called “dikes”)
[] Wire Stripper for removing insulation from wire
[] Assorted Screwdrivers (at least a couple sizes each each: slot and Phillips)
[] Assorted small wrenches, both traditional English and Metric
[] Soldering Iron (25 or 30 Watt “Pencil” type)
[] Quarter-inch Electric Drill and Assorted Drill Bits
[] Hack Saw with Blade(s)
[] Pocket Knife
[] Digital Multimeter (DMM) that measures Voltage, Current, and Resistance. You can get a basic DMM that is more than adequate to do all the measuring required for ten dollars, or less. For less than a hundred dollars, you can get a DMM that includes a transistor and diode checker in addition to measuring Voltage, Current, Resistance, Capacitance, Frequency, and Temperature.

Just about any DMM will serve you well. The DMM I use most, pictured below, is a cheapie that I purchased for $2.99 (plus tax) on “sale” at Harbor Freight a few years ago.

TIP OF THE DAY: Virtually all DMM’s come with a standard pencil-type test probe. The first thing I do with a new DMM is to remove the pencil-type probe tips and replace them with grabber-type probe tips, such as the ones shown here.


Grabber-type probe tips are relatively inexpensive, about $2.50 each, plus shipping, and they are worth every penny (and then some) when testing or troubleshooting. I use grabbers on all my test equipment.

[] 12 volt POWER SUPPLY. Like many things electronic, power supplies come in a variety of sizes and prices. For the project(s) presented here, you will need a power supply that can deliver a nominal 12 volts and current of about 2 amps. Most of the individual modules require only a fraction of an amp for testing and operation – – the Transmitter Amplifier module will require about 2 amps.

While not absolutely necessary, a REGULATED supply with ADJUSTABLE output and METERING for both Voltage and Current is a great help when building and testing circuits, particularly when powering up a circuit for the first time.

Power supplies are easy to obtain. If you don’t already have a suitable power supply, you can purchase one at most any electronic parts outlet. Also, don’t forget to check out your local Ham Radio club when looking for a power supply. With any luck at all, you can pick up a “loaner”, or perhaps even get one of your very own for free.

And, you can, of course, build your own power supply. The ARRL Handbook provides details for building a variety of power supplies.
If you already have a 12 volt power source that is not adjustable and/or metered, don’t worry about it. I’ll show you a way to work around that problem when we get to testing and troubleshooting.

NOTE: When doing circuit testing in general, and for testing newly assembled circuits in particular, always start at near zero volts and s-l-o-w-l-y increase voltage while monitoring the current. This way, if there is excessive current you catch it before your newly built circuit goes up in smoke because of a wiring error.

Yes, I occasionally make wiring errors, and you will, too – unless you are very good and/or very lucky.

I recommend the following OPTIONAL TOOLS in addition to the tools listed above.

[] Pistol-grip Soldering “Gun” (100 – 150 Watt). Seldom needed, but when needed, nothing else will do the job.

[] A GENERAL COVERAGE “SHORT WAVE” RECEIVER, preferably with digital read-out, such as the Grundig “Yacht Boy” pictured below. To be useful for Ham Radio purposes, the receiver must be capable of receiving Single Sideband (SSB) and Morse Code (CW) in addition to the more common AM and FM signals.

In addition to serving as a back-up receiver for your Ham Radio station, a well-calibrated receiver can serve as a frequency meter on your workbench.

If you already have a Ham Radio station for the high frequency (HF) bands, you station can serve as both a frequency meter and signal generator.

[] An electric “hobby” tool with assorted cutters and grinders. The “DREMEL” is one such tool, and there are other brands available.

[] Although an OSCILLOSCOPE is one of the most expensive pieces of test equipment, it is also one of the most useful devices for testing and/or troubleshooting electronic circuits. I purchased a Tektronix 465M ‘scope as military surplus several years ago, and it has served me well.

I hasten to add that an oscilloscope is NOT required for testing the circuits shown here, but it would be a great help in case one of the modules you have lovingly assembled just sits there and does nothing. To be useful for testing and troubleshooting Ham radio electronics, an oscilloscope should be rated at 100 MHz, or better.

One source for used oscilloscopes is

Fair Radio Sales .

Don’t forget to check out your local Ham radio club where you may find a “loaner”.

MISCELLANEOUS SUPPLIES

A list of generic supplies is shown below.

NOTE: While a complete parts list is provided for each module, you might want to buy some parts and supplies in bulk to have materials on hand when needed. For example, to build the complete transceiver you will use:
[] Radio Shack #276-148 Dual Printed Circuit Board, or equivalent. The exact number of circuit boards will depend upon how you package your finished transceiver and what optional features, if any, are included. About a dozen of these boards are required to build the transceiver with no optional features.
[] Electric Tape
[] Heat-shrinkable tubing (more expensive than tape, and much better for many applications) Be sure to get the NON-Conductive type of tubing.
[] Solder (Rosin Core, NOT Acid Core)
[] Insulated copper Hook-Up Wire. #24 or #26 in several colors. White, black, red, green, yellow, orange, and blue are commonly available. I prefer stranded hookup wire, as opposed to solid, because it is more flexible.
[] Enameled solid copper wire, sizes: #28, #26, #24. This will be used for fabricating inductors (coils) as needed. It is helpful to have at least three colors of enameled wire. If, for whatever reason, you want to have only two sizes of enameled wire, I suggest you use #26 and #24.

NOTE: The term “enameled” is used here to refer to the wire commonly referred to as “magnet wire”, which traditionally used enamel as an insulation material. Magnet wire manufactured these days uses a polyurethane/polyamide (nylon) insulation material.

[] Bare copper wire, #22. A total of about 12 feet of this is required for the Ground Buss and Tie Points on all the circuit boards used in the transceiver.

[] Two feet, or more (depending upon how, exactly, you choose to package your transceiver) of RG174 1/8 inch diameter coaxial cable.
[] About two square inches of single-sided printed circuit board.
[] Solderable sheet metal (preferably copper) for shielding.
[] A #10 nylon or teflon bolt with nut, about 3/4 inch long. Required for mounting the coil that determines the frequency of the variable frequency oscillator (VFO).

NOTE: If you choose to use two or more boxes to house the transceiver, various jacks and connector will be required for the cables between boxes. More about this when we get to final packaging and assembly.
PARTS

The photo, above, shows some of the cabinets in which I have stocked parts. I have been doing this sort of thing for well over 50 years, so I have accumulated lots of parts, and seldom have to order anything other that some “special” parts that don’t happen to be on hand when needed.

A COMPLETE PARTS LIST WILL BE PROVIDED FOR EACH MODULE.

I get many of my PARTS from discarded consumer electronics items and military surplus. I urge you to do the same. First of all, these parts are cheaper than ones you buy from electronic parts suppliers (if you ignore the cost of the labor you invest in salvaging the parts). Second, and probably more important, it is the “green” thing to do. It seems a waste for perfectly good electronic and mechanical parts to end up in the dump along with yard trimmings and kitchen garbage.
Having said that, I hasten to add that it is highly unlikely you will be able to find all the parts you need via salvaging.

If you simply cannot bring yourself to do salvaging, there are numerous suppliers eager to provide parts. The suppliers I use most:

JAMECO

MOUSER

Digi-Key

There are some parts that may be difficult to find via “normal” parts suppliers. These parts, I usually get directly from the company that makes them, or from an authorized distributor:

AMIDON

My source for toroidal cores required for some inductors, such as the inductors used in the filters for both the receiver and the transmitter sections of the transceiver.

Mini-Circuits

For the SBL-1 diode ring mixer used in the Product Detector module.

And, of course, there is always your friendly, neighborhood Radio Shack store, the source for the Radio Shack 276-148 Dual Printed Circuit Board, which serves as the foundation for virtually all the modules used in the transceiver discussed in subsequent parts of this series.

Equivalent circuit boards can be cut from bulk stock at much less cost, if cost is a concern.

If you live in or near a city with a population of 100 thousand, or more, chances are you have an electronic component supplier (other than Radio Shack) within easy driving range.

With electronic parts, as with other merchandise, it pays to shop around.

If all else fails, just Google the part of interest, and let Google find a supplier for you.

Next, we will take a look at Packaging in general, and the Radio Shack 276-148 Dual Printed Circuit Board in particular.

- END OF  TOOLS, SUPPLIES, and PARTS -

Labels: parts, supplies, tools

 

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WT40 INTRODUCTION

[[ Most recent Update:  20 November 2012. ]]

The emphasis here is on learning about electronics by doing it – not electronic theory, but how to put things together and make them work. The first project is a relatively simple 4o meter transceiver that I have named the WannaTinker 40 Meter Transceiver aka “WT40″.

The material you find here represents a major revision of a project that was previously published on my WannaTinker website, which no longer exists.

Parts one, two, and three are intended for those who have little or no experience with building electronic equipment.

Part 1 is an introduction (you are here).

Part 2 is a brief summary of Tools, Parts, and Supplies that will be needed to build the WT40.

Part 3 addresses Modular Building concept that is used for the WT40 transceiver.

Experienced builders are welcome to peruse parts 1, 2, and 3, but may want to start with Part 4 where the building process actually begins with

POPULATING the AUDIO AMPLIFIER CIRCUIT BOARD.
I CONFESS . . .

. . . I was born with no knowledge whatsoever about electronics, so everything you see here came from somebody else at some time in the past.

I try to give credit where credit is due, and if I know the source of the material I am using I will site the originator(s). I have kept notes and diagrams of circuits that have worked for me over the years, and those notes, along with specification sheets from component manufacturers are my main sources of information. Yes, I sometimes add a tweak or two to the circuits you find here, but I am a technician, not a design engineer.

Building electronic equipment from “scratch” is not everyone’s cup of tea.

CAN YOU DO IT ?

Sure, you can !

Given the desire, along with a bit of patience, persistence, and the ability to use simple hand tools and a digital multimeter (DMM), you can build a variety of electronic gadgets from “ground, up” (the importance of “ground” will be covered later in this series).

I have built, tested, and used every module presented here to insure that they work as intended.

Each and every project I build provides entertainment, education, and the satisfaction that comes from messing about with tools, components, and test equipment, not to mention the satisfaction I get from compiling and publishing the pages you see here.

Speaking of satisfaction – – powering-up a radio station you have lovingly assembled from a pile of parts can be a heady experience, indeed.

It feels good to be able to say “The rig here is home-brew”, and really mean it.

The project(s) presented here are related to amateur (Ham) radio, but the principles and techniques can be applied to other electronic devices.

If you are completely new to electronic circuit building and/or Ham radio, I suggest that you take a look at the ARRL Handbook for Radio Communications, which is available at most any public library, or can be purchases from many book stores, or directly from the American Radio Relay League (ARRL) , handbook.

Give particular attention to the “Construction Techniques” section.

One other suggestion for the inexperienced builder of electronic stuff:  find a local Ham radio club and attend a meeting or two. Most clubs are full of Hams eager to help you get your license, and some clubs can actually administer the tests required for the license. Not only that, but many Ham radio clubs have a “freebie” table set up at their meetings where you may find an ARRL Handbook and other interesting and useful things.

WannaTinker is intended for the inexperienced builder of electronic equipment who, for whatever reason, has decided to build something electronic. Experienced builders are certainly welcome to follow along as we look into practical ways to assemble and test electronic modules that will eventually be assembled to become a low-power transceiver that can be used on frequencies allocated for amateur (Ham) radio operators.

For those who are not (yet) licensed to operate as Ham radio operators, I hasten to add that you must have a license from the Federal Communications Commission in order to legally TRANSMIT on any of the Ham radio bands. You can, of course, listen to any of the radio bands allocated for use by Ham radio operators.

You can find out about becoming a Ham radio operator by visiting the American Radio Relay League (ARRL) , getting- license.

MODULAR BUILDING TECHNIQUE

After building numerous pieces of electronic gear, I have settled into a modular building technique that has served me well. By dividing the various circuits that make up a piece of gear into small modules, then assembling the modules into the final unit, the process of building, testing, and (when necessary) troubleshooting is much quicker and easier than other techniques I have tried.

A five-step procedure for building each modules:

[1] Collect all parts required for the module.

[2] Prepare the circuit board.

[3] Populate the circuit board.

[4] Perform initial check-out of the circuit board.

[] Visual Check

[] Resistance Measurements

[] Current Measurements

[] Voltage Measurements

[5] Operational Test

BUILDING PROCEDURE WILL BE DETAILED FOR EACH MODULE

A home-brew project is just that, a p.r.o.j.e.c.t – a work in progress.

I have never built anything that could not be improved upon. Most of my home brew stuff is, therefore, never quite finished. There are some things I have built and used, unchanged, for years. Sooner or later, however, I simply must take the covers off and “improve” the device.

Some work better.

Some look better (or worse). Some show little or no change in appearance or performance.

Some never recover from the “improvement” and end up being cannibalized for parts.

One of my “keepers” is the little QRP transceiver shown below.

The “box to put it in” once housed an “A – B” switch for the serial port on a computer, and measures about 5 7/8” Wide x 2 3/8” High x 6” deep. Packaging is a matter of personal preference, and will be addressed later.

For this WannaTinker series, we will spread things out to make building and assembly easier. Also, the radio we (YOU and I) are building here will not have some of the optional features included on the version shown in the photo. This series of articles is, after all, about discovering the pleasures of building your own equipment, not about producing the world’s best radio.

Having said that, I hasten to add that this little transceiver is capable of world wide communications, given good radio propagation conditions and a good antenna.

Speaking of the world’s best radio, the relatively simple radio featured here will certainly not be “the best”, but it may turn out to be the best loved because you will have built it with your own hands.

Next, we will take a look at tools, supplies, and parts required for building electronic circuits.

- END OF PART 1, INTRODUCTION -

 

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Welcome to the WannaTinker, WT40 Project

[[  Mos recent Update:  20 November 2012.  ]]

The WannaTinker 40 meter transceiver, aka WT40, was designed with the inexperienced builder of electronic circuitry in mind.

The WT40 serves as a vehicle for learning about electronics by doing it – not electronic theory, but how to put things together and make them work.

Having said that, I must point out that there are times when a bit of theory will come in handy – for example, if a project you have lovingly assembled simply sits there and does nothing at all, it may be helpful to know a little about how components are supposed to work in a given circuit.  Accordingly, from time to time, we will explore briefly some fundamentals of how electricity acts under certain conditions.

The material you find here is a major revision of a project that was previously published on my wannatinker.com website, which no longer exists.

Parts one, two, and three are intended, primarily, for those who have little or no experience with building electronic equipment.

Part 1 is an Introduction.

Part 2 is a brief summary of Tools, Parts, and Supplies that will be needed to build the WT40.

Part 3 addresses Modular Building concept that is used for the WT40 transceiver.

Experienced builders are welcome to peruse parts 1, 2, and 3, but may want to start with Part 4 where the building process actually begins with

POPULATING the WT40 AUDIO AMPLIFIER CIRCUIT BOARD.

If you want to see it all, go to  WT40: INTRODUCTION

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