On Sun, 21 Jul 2019 at 01:52, Dan Rae via Groups.Io <danrae=
[email protected]> wrote:
On 7/20/2019 4:13 PM, John Woods via Groups.Io wrote:
Hi Mike
I am also missing the "short" from the calibration set.
I'll let you know if I get anywhere with a complaint I've put in to the
vendor,.
Good luck with that! I also had the Short missing and didn't think the
vendor would even know what I was talking about, but it was pretty easy
to make one with a PC mount male SMA and a scrap of brass foil left over
from making the absent shields on mine.
Well, if something is missing that should be there, then if bought from
eBay, I would stick in an ¡°item not as described ¡° claim.
My company
produces VNA calibration kits, so I know a fair bit about how they should
be designed. Since the nanoVNA doesn¡¯t allow one to specify a delay of the
short, any attempt to make a short the way you are doing will be worst than
having a proper short.
The short supplied with my kit looks like it is an Amphenol one, which are
not very good, but will be better than you can make the way you describe.
I have not verified it yet, but I think that you will be better not using
the open standard at all, as that will add unwanted fringe capacitance, so
make the open less like the idealised open I believe that the code expects
to see. At 900 MHz an SMA connector will not radiate, so there¡¯s no need to
shield the conductor.
While I was at it I made a good
Load with two 100 Ohm 0.1% 805 Rs on another SMA. This is a lot closer
than either of the Loads that came with mine.
You really need to test that at RF frequencies though. I have some loads
with a measured return loss of at least 45 dB at 900 MHz, although the
uncertainty in the measurement is fairly high as the loads I used for
calibration, which are the loads in my 26.5 GHz 3.5 mm HP 85052B VNA cal
kit, have a return loss of at least 48 dB.
Unfortunately I could not sell our loads at price of a nanoVNA, so it¡¯s
unlikely nanoVNA uses would want them.
For what is seemingly "a bad clone" I'm pretty happy now with it's
performance.
Good.
Dan - ac6ao
Dave, G8WRB.
--
Dr. David Kirkby,
