20W Dummy Load Kit Assembly Guide

Assembly Procedure

1. Prepare your workspace

   Find a clean, well-lit area to work. Collect your kit components and tools. You will need the following:

   • Soldering iron
   • Flux-core solder, or solder and solder paste
   • Small wire cutters
   • Needle-nose pliers (optional)
   • Multimeter for testing (optional)
   • Helping hands, or similar device, to hold the components while soldering

2. Inventory the parts

   Open your project bag and verify that all the components are there. You will have the following:

   Count	Item	Image
   1	Printed circuit board (PCB)
   8	100 Ohm resistors
   1	Shottky diode
   1	Ceramic capacitor
   1	BNC connector

   If anything in your kit is missing or damaged, please contact me at de.k7rhy@gmail.com. I will send you a replacement part.

3. Prepare and install the resistors

   Install the resistors on the PCB at the locations marked R1-R8. All the resistors are identical, so they can go in any of the marked spaces; orientation isn't important since the resistors are not polarized. If you're experienced with electronics, you can install all the resistors on your own now. If you're new to soldering, follow along with my instructions.

   1. Prepare the resistors

      Bend the leads of the resistor so that they are at a 90-degree angle to the body of the resistor. This will make it easier to install the resistor on the PCB. Use the PCB as a guide to determine the correct lead spacing.

      

   2. Insert resistors R1-R4

      Insert the first four resistors into the PCB at the location marked R1-R4. The resistors can go in either way; there is no polarity to worry about. Once installed, bend the leads outward slightly to hold the resistors in place. The resistors should be flush with the PCB and on the printed side of the board.

      

      Understanding Your Options - Resistor Height

      There is a balancing act in play here. By placing the resistors flush with the PCB, we're limiting the air flowing around them, which limits the amount of heat/power they're able to passively dissipate. However, by keeping the resistor leads short, we're reducing the parasitic inductance in the circuit, thereby lowering the SWR of the device at higher frequencies and increasing its efficiency. This is a trade-off that I made based on my personal preferences; you are welcome to make other choices.

   3. Solder the resistors

      Hold the soldering iron to the pad and the lead of the resistor on the back of the PCB. Touch the solder to the joint, not the iron. The solder will flow onto the pad and the lead. Remove the solder first, then the iron. The joint should be shiny and smooth. Repeat this process for all the resistors.

      

   4. Trim the leads

      Use the wire cutters to trim the excess leads from the resistor on the back of the PCB.

      

   5. Repeat for the remaining resistors

      Repeat the above steps for the remaining resistors, installing them at the locations marked R5-R8.

      

4. Install the capacitor and diode

   Install the components at the locations marked C1 and D1 on the PCB and solder them in place. Trim the leads after soldering.

   1. Install the capacitor

      Insert the capacitor into the PCB at the location marked C1. The capacitor is not polarized, so it may be installed in any orientation.

      

   2. Install the diode

      Insert the diode into the PCB at the location marked D1. The diode has polarity, so it must be installed in the correct orientation. Match the black line on the diode with the white line on the PCB silkscreen. Position the diode with the black line closest to the edge of the board, facing away from the resistors.

      

5. Install the BNC connector

   The installation of the BNC connector is tricky because of the alignment of the leads. Follow these steps carefully to ensure a good connection.

   1. Prepare the BNC connector

      Bend the leads of the BNC connector back roughly 30 degrees. This will make it easier to install the connector on the PCB.

      

   2. Insert the BNC connector into the PCB

      Begin by inserting the leads of the BNC connector into the PCB at an angle, into the location marked J1. They are very short, so starting this way will make sure that everything is aligned correctly. Once aligned, press the connector down flat on the PCB. It will fit snugly.

      

   3. Solder the BNC connector

      Soldering one of the mounting posts of the BNC connector before soldering the leads. Hold the soldering iron to the pad and the post of the BNC connector on the back of the PCB to heat it up, and apply solder. The posts are thick, so they will take a little longer to heat up. The posts are not connected to the circuit and are only for mechanical support. Once the posts are soldered, solder the connector leads. The leads will not need to be trimmed.

      

   4. Appreciate your work

      Congratulations! The assembly is complete. Now it's time to test your build. Testing is an important step that ensures your dummy load will work correctly when connected to your radio.

      

6. Verify the build

   Before connecting the device to your radio, perform a final inspection of the assembly.

   1. Check for missing parts

      Confirm that all the components are installed correctly and that no parts are missing. Aside from TP1 and TP2, there should be no marked areas of the board that do not have an attached component. There should be no empty holes on the board.

      

   2. Inspect solder joints

      Inspect all solder joints to ensure that they are shiny and smooth. If not shiny, apply your soldering iron to the joint to reflow the solder. There should be no solder bridges between adjacent pads, and no solder balls should be present on the PCB.

      

   3. Verify resistance

      Using a multimeter, measure the resistance between the two leads on the back of the BNC connector where it connects to the top of the PCB. The resistance should measure between 47.5 and 52.5 ohms. Slight deviations from that range are acceptable, but any major deviations may indicate a problem with the assembly or components.

      

   4. Check diode orientation

      Verify that the black line on the diode matches the white line on the PCB silkscreen. The diode should be oriented with the black line closest to the edge of the board facing away from the resistors, with the lead going through the hole labeled K.

      

Precautions