Dilshan R Jayakody’s Web Log

Resistor box is a quite useful instrument in analog electronic based design and prototyping tasks. It can easily build with few sets of resistors and with a couple of rotary switches. This quick post is about resistor box which we construct recently using 5W wire-wound power resistors. For this resistor box, we use five, single pole 12 position rotary switches and 50 wire-wound resistors. It gives 5 dials to controls 10Ω, 100Ω, 1KΩ, 10KΩ and 100KΩ steps. Final view of homebrew resistor box. Internal view and high-resolution photographs of this resistor box are available at my Flickr page . Schematic of the resistor box is available here .

This is a quick post about 100W RF dummy load which we build to use with HF and VHF transmitters and transceivers. This dummy load uses two non-inductive 100Ω 50W thick film power resistors manufactured by Vishay Sfernice and both these resisters are connected in parallel to achieve 50Ω impedance. The final version of 100W RF dummy load. Outer-casing (which also act as a heatsink) of dummy load is constructed using four bonded fin 50mm × 115mm × 20mm heatsinks. During our testing, we got flat 1:1.2 SWR with this dummy load. Internal view of 100W RF dummy load. Above mentioned 100Ω 50W power resistors are obtained through Farnell element14 .