On Fri, 4 Oct 2019 at 13:38, Martin via Groups.Io <martin_ehrenfried=
[email protected]> wrote:
i 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.
Whilst agreeing on his return loss statement, the blog is written in a
childish condescending way. If anyone wants to forward him the post I made
about how the HP LCR meter can display things, they are welcome to, but I
can't be bothered to communicate with people like that.
Dave
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
--
Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
Essex, CM3 6DT, United Kingdom.
Registered in England and Wales as company number 08914892
Tel 01621-680100 / +44 1621-680100
