 |
 |
 |
 |
Usually, we Hams want all the signal strength we can get, but there are times when plenty is too much. Some of our circuits are sensitive and can be overdriven into distortion or even damage. Fixed attenuators are handy things to have around, but a step attenuator is even more useful as you can set it for the exact number of dB down you want. Such devices, controlled by switches, have been around a long time, but they’re often big and clunky (and you end up paying more for the clunk). They’re a little tricky to homebrew because you want to make sure you maintain a 50Ω impedance throughout.
But digitally-controlled step attenuators have been developed for the cell-phone industry, and we can make use of them, too. The DSA-1 will use two Mini-Circuit’s DAT-31A-PP+ chip for step attenuation from 1dB (the insertion loss) to 62dB. It takes care of maintaining impedance, it’s good from DC to 4GHz, and it’s controlled by a five-bit parallel port–yet one more task for our beloved (ahem) microcontrollers. The DSA-1 will have a two-digit display and attenuation will be set by rotary encoder. It’ll also have a USB connection for remote control and for charging its internal lithium battery.
For a specific instance in which input attenuation was needed, see W2AEW’s YouTube video, Use a NanoVNA to measure input impedance and gain of a small-signal RF amplifier.