An RF attenuator is useful in a lot of RF projects where a signal level is not what you need. Lab attenuators often come in steps, and the very fancy ones can be controlled either manually or by a PC. Keysight makes some nice ones, like the 8494G (1dB steps from 0 to 11dB, 4GHz) or the 8495G (10 dB steps from 0 to 70dB, 4GHz), but they were not perfect for what I wanted. Here is why:
- You need two of them to obtain 0-32dB (the range I needed).
- New price is around 2K€ and 1.7K€, respectively
- Attenuation tolerance is 0.6dB and 0.4dB (at 0dB setting !), respectively
- You need a special power supply to run this
What I did not need is the 4GHz range. I would be fine with 0-100MHz, but I would love a 0.2dB accuracy at 10MHz and below. So – its homebrew time. Some 1% metal film resistors, some miniature relays, an Arduino and this is what we get:
- 0-32dB in 1 dB steps
- 1W Maximum
- Accuracy 0.2dB at 10MHz at all settings, 0.5dB up to 100MHz, 1dB up to 200MHz
- S11 better that 13dB at all frequencies, better than 20dB below 10MHz.
- SCPI Controllable or local operation.
- USB powered
- Cost about 100€.
Look here for some more details and measurement results
Electronic Projects for Fun 