Assemble a radio kit - from unpacking to operation. The build involves soldering basic electronic components, including integrated circuits and transistors, and tuning the local oscillator. Included are many hints and tips, as well as a simple alignment procedure.
The purpose of this submission is to demonstrate through-hole electronic assembly. Single examples of each component's installation are presented so as to minimize repetition. No doubt everyone has their own way of doing things, but I hope there's something useful for you here.
Step 1: Watch the Video
Step 2: Gather the Tools, Examine the Contents, Read the Manual, and Inventory All Parts
Before starting, ensure you have all the necessary tools and supplies. In this case, the following are useful:
- Soldering iron - anything between 25W and 60W should do.
- Wire cutters, sometimes called side cutters or dikes.
- Needle-nose pliers.
- A "third hand", supporting vice or some such is very useful, but not essential.
- Solder to match the project - leaded for non-ROHS projects, lead-free otherwise. Make sure it's NOT acid core solder.
- Isopropyl alcohol or equivalent, for cleaning off the solder flux.
- Cotton balls or tissue paper.
- An old toothbrush is useful too. DON'T use it for your teeth afterwards!
- If possible, find a plastic alignment screwdriver. It's not essential, but does minimize potential problems.
The first step in construction: read the manual from cover to cover! Afterward, inventory every part to make sure you have everything before starting.
Step 3: Clean the PCB and Mount It
Use the alcohol and tissue or cotton swabs to clean just the copper side of the PCB. Don't clean the component side, as the parts diagrams and legend might be removed. If you have a third hand or supporting vice, mount the board in it.
Step 4: Prepare the Soldering Iron
With a damp sponge (not wet), clean the tip of the hot soldering iron while applying fresh solder to it. This is known as "tinning" the iron. It makes for neater and more reliable solder joints. Watch the video to see how.
Step 5: Before Beginning: Non-polarized Vs Polarized Components
Some electronic components are not polarized, that is, it's not important which way they are installed. In the first image above, some non-polarized components are shown: a crystal, a couple of ceramic capacitors, and a resistor.
Some components are polarized. They ARE sensitive to orientation. If they are installed backwards, the resulting project won't work correctly, and the part might be damaged. The second image shows such parts - three integrated circuits (ICs), an electrolytic capacitor, a transistor, and a diode.
Step 6: Follow the Manual's Suggested Construction Sequence
If the manual lays out a construction sequence, follow it precisely. If not, a typical order is:
- Mechanical parts, such as switches, sockets, potentiometers, etc.
- Coils and inductors (depending on mechanical fragility, these might be installed later)
- Ceramic capacitors
- Other capacitors, excluding electrolytics
- Electrolytic capacitors
- Diodes and transistors
- Integrated circuits
Sometimes board layout or other constraints force a different ordering.
Step 7: Install the First Component: a Switch
A switch is the first mechanical component on this project. Although it would be difficult to insert backwards, it never hurts to double-check. After every part is installed, check for solder bridges and other defects ( missed pins, etc.).
Step 8: Install the Antenna Socket
Antenna sockets and the like often have additional mount tabs for sturdy attachment to the board. Ensure they are well soldered (but not "drowning" in solder).
Step 9: Install the Speaker Socket
As this part is subject to mechanical stress (like the antenna socket), ensure the speaker socket is well soldered to the board. This particular socket has long lugs. After soldering, use the wire cutters to snip the excess length.
Step 10: Install the Potentiometers
There are three "pots" on this project. These too have significant mount tabs. Solder them well.
Step 11: Installation of "Mechanical" Parts Is Complete
Step 12: Install the First Capacitor
In this project's case, the manual specifies a ceramic capacitor first. Always follow the manual's advice. Ceramic capacitors are non-polarized, so orientation is not important. However, it's considered tidy to face the legend or body markings all in the same direction. When done soldering the leads, clip away the excess with the wire cutters.
Step 13: Shape the Leads and Install the First Transistor
Often, transistor legs must be bent or shaped in order to fit in the right holes on the PCB. Here it's best to watch the video to see how. A transistor is a polarized part. Which way the middle leg is bent determines the part's orientation on the board. So take care to bend it in the right direction.
Transistors can be temperature sensitive, so don't spend more time than necessary soldering the legs.
Step 14: Shape the Leads and Install the First Resistor
Resistor leads typically must be bent to fit into the board. Here I'm using a template, but a pair of needle-nose pliers work just as well.
A resistor is a non-polarized part, so its orientation is not critical. However, similar to ceramic capacitors, it's considered tidy to keep the "tolerance" stripes of the resistors pointing in the same direction (e.g. all to the right). If you don't know the color codes, manuals typically explain them, and there are many online resources.
Step 15: Install the First Integrated Circuit (IC)
ICs are polarized parts and must be installed with the correct orientation. Usually there's a notch on one end for this purpose.
Sometimes the legs of the IC must be bent inward to fit the matching PCB holes. If necessary, do so very carefully by placing the legs on one side of the IC down on a flat surface and applying gentle pressure. Repeat for the legs on the other side.
It can be awkward to solder the IC and keep it in place at the same time. If so, the adhesive tape trick shown in the video works well. If the IC does slip after soldering the first leg, reflow the solder on that leg while pressing the body of the IC to the PCB.
Like transistors, ICs can be heat sensitive, so don't solder longer than necessary (while at the same time ensuring good solder joints).
Step 16: The Two Quite Different Ceramic Filters
In this project, two ceramic filters are used. One is not polarized (in the first picture), whereas the other is (second picture). The latter cannot be installed incorrectly due to its asymmetrical pin layout.
Step 17: Carefully Sand Tarnished Leads
If any leads are tarnished, solder might not adhere well. Gentle sanding can bring the legs to a bright finish. In the image above, sanding is necessary for an RF coil.
Step 18: Periodically, Clean Off the Flux
Every now and then, clean the accumulating solder flux from the board. Not only does this result in a neater appearance, flux can hold solder whiskers and fragments which might short PCB tracks together. Also, over time, flux can absorb moisture - never a good thing for PCBs.
Step 19: Install the First Electrolytic Capacitor
Electrolytic capacitors are polarized, so orientation is important. These days, most electrolytic capacitors identify their negative legs with a '-'. Yet oftentimes the PCBs identify where the positive legs should go, marked as '+'. In such a case, simply insert the negative leg into the hole NOT marked '+'.
Step 20: Install the Crystal
Crystals are typically non-polarized. However, they can be mechanically delicate.
Step 21: Install a Diode
Diodes are polarized. Note the stripe on the body in the first picture, and ensure it is inserted as indicated by the figure on the PCB (second picture). Like transistors and ICs, don't heat them more than necessary.
Step 22: Continue Until Completion, Then Double Check Everything
When assembly is complete, it's vital to check carefully for dry solder joints and solder bridges. A good solder joint is shiny and attached well to both the wire lead and the PCB track (not balled up). A dry solder joint is typically dull or fractured. Solder bridges are whiskers of solder - or wire even - that bridge copper tracks where there should be no connection. Reflow any poor or dry solder joints, and remove any whiskers or bits of errant wire.
It's also vital to go through and check the orientation and placement of every component. We are all human and it's so easy to install a part backwards or in the wrong place!
Step 23: Substituting a Longer-Lived Battery Pack
In this project, I decided to substitute the original PM3 9V battery clip with a 6xAA battery pack. Eventually, this project will be protected by an enclosure and I plan on leaving enough room for the AA pack. With the substitution, I should get significantly longer operation before needing to replace the batteries. The battery pack here has a PM3 connector, so no additional soldering or connector changes are necessary.
Step 24: Align the Local Oscillator
The local oscillator on this radio operates at 10.7 MHz above the received frequency. The band spread for 2 meters runs from 144 MHz to 148 MHz. So when the tuning dial is at its midpoint, the received frequency is 146 MHz and the local oscillator must run at 146 + 10.7 MHz, which is 156.7 MHz. The manual explains further if my description here is opaque.
A very simple method of alignment is with a scanner tuned to 156.7 MHz placed right next to the newly constructed board. Apply power to the new board and set the tuning dial to its midpoint. Adjust the local oscillator coil's tuning slug (preferably with a plastic alignment screwdriver) until there's a burst of noise from the scanner. At this point, the local oscillator is aligned.
A scanner is not essential, but it does make alignment easier. If you don't have one, follow the manual's procedure.
There's another adjustable coil on this board. It must be tuned to maximize the output level (volume) - a very straightforward process. Follow the manual for more details.
If possible, avoid the use of a metal screwdriver. Not only does the metal affect the tuning - making it harder to align the receiver - it can also damage the ferrite slugs if too much force is applied.
Step 25: Attach Antenna and Speaker, Then Seek a Station!
If all has gone well, there's little more left to do apart from attaching an antenna and speaker to the mint receiver. Turn the volume up and the squelch down, then hunt for a station with the tuning dial!
Step 26: Attach Knobs and Temporary Feet
For the moment, I'm using temporary feet until I make an enclosure. Also, I've attached knobs to make the receiver easier to operate.