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I believe the point that Dave Jones was making, is that the surface
resistance of the mats does not have any adverse effects on 99.99% of the
measurements one makes. I don't think his aim was to show how good a
static dissipative mat was - only that it does not have any adverse
reactions.

It's generally considered unsafe to ground the mats - instead they should
be connected to ground by via a high-value resistor - typically 10 M ohm.

I personally don't think people need to worry about static on the test
ports of the NanoVNA. However, since the sides of the NanoVNA are open in
the standard unit, then there's a possibility of static doing damage there.

Dave

On professional VNAs, stimulus source is calibrated for flatness on
factory with a bolometer. On nanoVNA you can't control stimulus output
power, so we should probably calibrate the audio codec gain to get most of
it's dynamic range at each frequency, or at least for each band. However
multiple mixing products, others than the desired one, could be present at
audio frequencies, so this must be done with care.

This could also lead to a debate about needed headroom to measure DUTs
with gain. IMHO, it would be better to sacrifice having a lot of headroom
and just insert an attenuator if an amplifier S21 is to be measured.

I have not taken a look to the code in much detail yet, maybe this is
being done, but probably not. I have read somewhere that people have
measured their LNA's gain, so current code must be setting the codec gain
too low if it has so much headroom and the S21 70-80dB noise floor we are
seeing could be in fact being limited by the codec dynamic range.

I also miss an averaging mode, as some measurements are quite noisy, and
it would help for duplexer adjustments with notches near the VNA noise
floor. Maybe just a moving average low pass filter with just 2 taps to
avoid increasing memory requirements (new=0.9*last+0.1*meas). David
mentions using averaged measurements for isolation, and in fact most
professional VNAs use averaging when performing calibration.

Carlos

On Sun, Sep 22, 2019 at 06:09 AM, Mario Vano wrote:

CORRECTION: (I mistyped)

- The multi-band dipole is my 20ft high 40/20 meter trap dipole that has
been augmented with parallel dipoles for 15 and 10. The feedline has a
toroid common mode filter.

I've been happily using the NanoVNA and various versions of "Saver" for

a lot

of projects lately, but some were just motivated by curiosity about the
device.

Unfortunately I have no other analyzer to compare to. In any case here

are

some sweeps from earlier tests that might be useful for reference or
amusement. In most cases, they were done with my very early attempts at

full

bandwidth calibration.

- The fm filter is a commercial product from the rtl-sdr.com people.

- The LW filter is a homebrewed design I use to augment VLF beacon

hunting.

- The multiband dipole is my 20ft high 80/40 meter trap dipole that has

been

augmented with parallel dipoles for 15 and 10. The feedline has a toroid
common mode filer.

- The 6 meter antenna is an attic mounted dipole with a toroid common

mode

filter.

I've also used happily used the device and "saver" to design and build a

6

meter "squalo", but forgot to save the files from the latest testing

run. I'm

currently working on a 400-700 mhz indor LPA design and plan to try to

use the

device for relative pattern and gain testing.

Earlier tests with several types of 500-900mhz 1/4 wave mag-mount

antennas and

TV rabbit ears showed useful relative gain results at 2-3 wavelength

spacings.

73, AE0GL