Hi All,
Owen Duffy has recently posted a note about the Nano VNA on his blog.
He makes a few points about the accuracy of calculated values with both the Nano VNA and Saver in particular.
If we first deal with the issue of Return Loss, which is probably the most problematic par, and has certainly caught me out on several occasions.
Just about every instrument I can remember using, has RL shown as a negative curve, even if the units themselves are positive. This is handy if for example you are tuning a filter, as you can see the insertion gain on the uppermost trace and the RL loss on the lower one without them overlapping. It also matches the convention of SWR plots and when measuring the RL of cables it matches the convention of more attenuation being negative.
However Owen makes the point that negative loss is actually gain (double negative) and vice versa, and the existing conventions do indeed lead to confusion and mistakes being made. Maybe return loss should really be called return gain, and then everyone would be happy (well maybe - but this is not a serious suggestion).
However if we put this to one side, there is still the issue of how the values are being calculated, and if they are in fact correct. If not then I think this should be investigated in more detail and fixed, as there would seem to be an opportunity to do this before it propagates further.
Regards,
Martin - G8JNJ
