Tuesday, October 29, 2019

Checking Step Attenuator with NanoVNA

I decided to check the step attenuator with the NanoVNA.  It would be nice to see what the linearity of the step attenuator is across the frequency range I am interested in.  After calibrating the VNA I did a series of sweeps from 1 - 250 MHz. This uses the fundamental frequency range of the VNA, it uses harmonics for higher frequency measurements.  I first did the readings using the VNA's internal display, and then repeated with the PC based software.

With 0 dB selected the sweep showed about 2.4 to  2.6 dBinsertion loss .

The VSWR was between 1.05 and 1.1.  These values will work well for anything I plan on doing.  

I then did a series of sweeps at 10 dB incremnts on the attenuator.  The linearity is within about 1 dB throughout the range.


20 dB
30 dB
40 dB.
50 dB.
60 dB.

The linearity looks good across the entire range, within 1 dB.  With an insertion loss of around 2-3 dB in all ranges, which is more than adequate for what I need.  Trying to decide if I want to modify the attenuator firmware to show the actual attenuation or leve it as is.

The autoscale feature of thes PC software  really makes it easy to to get values across such a wide range without loosing resolution. The noise on the sweeps at higher attenuation levels, is due to the sensitivity of the VNA, but is still quite remarkable for a $50 instrument.  I am quite happy with both of these pieces of equipment.  The VNA does many of the things I wanted to do with a version 3 SNA Jr, so I will put off that project and work on several othr things I have been planning.