N 6 H I
Presents:
The Joy of Kit Building!
If you can solder, and use basic hand tools, you can have FUN,
and save money building your own ham radio equipment!
Building your own equipment definitely is still an option for today's ham radio operators! Amateur radio suppliers such as Elecraft, Oak Hills Research, Ten-Tec, Far Circuits, Kanga US, Milestone Technologies, Ramsey, Small Wonder Labs, Wilderness Radio, Hobbytron, Jackson Harbor, Vectronics, Almost All Digital, and many others offer state of the art equipment in KIT form, supplying all the parts needed to build your own homebrew ham equipment.
This web page will describe the process of building a typical electronic kit. Large photographs will document the key steps of the construction process, using the Oak Hills Research Model WM-2 QRP Wattmeter as an example electronic kit.
There are several significant advantages to building kits over purchasing factory-built equipment:
1. Cost Savings (The example kit in this article: $109.95 KIT vs. $174.95 BUILT - a 37% savings!)
2. When you build it yourself, you will really know what is inside the box,
and have a better understanding of how it works.
3. If the equipment ever develops a problem, you can probably fix it if you built it!
4. There is a certain pride in operating a piece of equipment that you built yourself, not to mention
showing it off to visitors in your shack, especially other hams!
5. Kit building is FUN and home construction allows you to take part in
one of the traditional joys of amateur radio: electronic construction!
Maybe the hardest part of kit building is simply waiting for the kit to arrive after you have ordered it! The WM-2 QRP Wattmeter Kit was shipped well-packed in a 7x7x6" box, and I was happy to see that particular care was given to protecting the nice quality case, knobs, front and rear panel overlays, and the meter itself to ensure that they would not be scratched, dented, or broken in transit. You may find that using a couple of egg cartons is a handy way to sort out the parts by category, placing all the resistors, capacitors, nuts and bolts, etc, in different sections to make it easy to find them easily during construction.
Here are the parts needed to build the QRP Wattmeter ... all 123 of them! That makes it sound more elaborate and complicated than it really is, because the parts count includes every single nut, bolt, and lockwasher, as well as the electronic components that need to be soldered on the circuit board and assembled into the case. Once the inventory has been taken, you are ready to begin construction of the kit. This kit provides a construction manual with very complete, clear, step-by-step instructions, similar to the old "Heathkit" manuals of years gone by. A space is provided to check off each step as you perform it, with individual steps for soldering each component, and assembling each mechanical part. If you carefully follow the manual, take your time, and check off each step as you perform it, you will find the kit easy to build. The construction for this kit will be in four stages: (1) Circuit Board Assembly, (2) Cabinet Preparation, (3) Final Assembly, and (4) Alignment.
Tools and equipment required for construction and alignment include basic hand tools; a LOW WATTAGE pencil type soldering iron with a SMALL tip, and rosin core solder, wire cutters, wire strippers, small and medium phillips screwdrivers, small flat blade screwdriver, needle-nose pliers, ruler, magnifying glass, and a bright table lamp or other well lit work area. A digital voltmeter or multimeter is the only test equipment required for alignment and calibration of the Wattmeter.
The first stage of construction will be to solder the components on the circuit board. Here is a close-up view of the "bare" circuit board. As you can see the locations for each component are marked on the component side of the board, and you can see the circuit traces showing through from the bottom side. The board is pre-drilled for each component, so you only need to follow the step-by-step instructions in the manual and solder each component, one at a time, onto the circuit board, and clip off the excess component leads after each part is soldered. A couple of suggestions here: Use a very small low wattage soldering iron, and be careful not to "bridge" any of the circuit traces with excess solder. Inspect your work carefully after each step, checking your solder connections with a magnifying glass and good lighting to make sure each step is a "GO" before proceeding.
Here is the completed circuit board assembly, with the 2 rotary switches and other connection wires all in place, ready to mount into the case during the final assembly stage of construction. Note the two small toroid coils with short lengths of coaxial cable passing through them at the top of the board. The coils will be wound as part of the circuit board assembly stage. It is an easy job, and the manual explains the process to wind these two identical coils. The four blue trimpots are used to align and calibrate the meter after construction is completed.
The next stage of construction is the cabinet preparation, which is simply the process of applying the front and rear panel vinyl labels which not only provide the necessary function labels for switches and jacks, they also really dress up the project and give it a very professional appearance for a "homebrew" kit-built product. I encourage you to read the manual section on applying the labels very carefully, take your time, and use great care in applying these labels so they end up nice and straight. If you warm up the labels a bit first by placing them near a lamp the adhesive will soften and make the job a bit easier, just be careful to only slightly warm them, you don't want to melt them!
Here you see the cabinet with labels attached, the completed circuit board assembly, and the other remaining components, ready for the final construction stage. Just like with the circuit board construction, the manual will guide you, step-by-step, through the mounting of the circuit board, battery holder, switches, power and coax connectors, and the meter movement into the cabinet. The manual steps will specify exactly which hardware to use to mount which components and where. As cabinet components are mounted, the circuit board and other components leads are soldered to complete the construction.
Here is the completed Wattmeter, ready for alignment and calibration. The alignment process is easy, but I suggest taking an extra minute or two to make sure that the alignment adjustments are set as accurately as possible, to ensure that the finished product will perform to its rated specifications and provide accurate power measurements. Alignment consists of adjusting the four internal trimpots to obtain specific voltage readings on a digital voltmeter, then once all the adjustments are completed, you clip a jumper wire on the circuit board, and the unit is calibrated and ready to use.
The WM-2 is a complete kit, but will require a couple of non-supplied items for use. In addition to the radio equipment you will use it with, you will need to supply a +9Vdc to +13Vdc power supply OR a standard 9V battery. You will also need to supply the 50 ohm coaxial connector cables to connect between the transmitter and Wattmeter, and between the Wattmeter and the load (antenna or tuner). If you are using an antenna tuner ("transmatch") the Wattmeter should be placed between the transmitter and the Tuner.
Here is a photo of the completed Wattmeter. The WM-2 is a QRP (low power) Wattmeter, offering 3 measurement ranges for both forward and reflected power: 10 Watts, 1 Watt, and 100 milliwatts Full Scale. This device is useful down to power levels as low as 5 milliwatts! The WM-2 can be used with transmitters anywhere in the range of 300Khz to 54 MHz, and consumes only about 1mA of current from its power source, making it ideal for field or portable use.
Although this web page describes the construction of a particular kit, the process involved is typical, and hundreds of kits are available today in the marketplace. Be aware that the complexity of various kits will vary, with some being easy enough for "rank beginners" and some possibly requiring more advanced skills and the availability of anything from no test equipment at all to possibly rather sophisticated test instruments for adjustment and alignment.
Those interested specifically in the WM-2 Wattmeter kit will find detailed specifications and pricing information for the kit available on the internet at:
http://www.morsex.com/ohr/wattmeter.htm
A nice concise, simple description of basic tools for electronics construction may be found at:
http://www.electronics-project-design.com/ElectronicTools.html
If you are new to soldering, a nice 7-minute video describing proper soldering techniques may be found at:
http://www.curiousinventor.com/guides/How_To_Solder
The kit described here uses no Surface Mount Devices but some kits do! A 9-minute video describing soldering techniques for these SMD's may be found at:
http://www.curiousinventor.com/guides/Surface_Mount_Soldering/101
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