开云体育

Can you show the measurement? preferably the smith chart of another VNA doing the CH0 measurement.

It makes a lot of sense.
From 0-300MHz you get the 2mA drive fundamental and its harmonics
From 300-900MHz you get8mA drive with fundamentals from 100-300MHz and its harmonics from 300-900MHz
So between 100-300MHz you see the fundamental of the 300-900MHz 3rd harmonic output.
To verify this you should do separate measurements for 0-300MHz and 300-900MHz

Bruce,
There were a couple of accompanying articles to the previous one that go into further detail.
and

It seems that CH0 output also has impedance about 40 Ohm. So, it's better to use two 10 dB attenuators. One on the CH0 and the second on CH1.

On Mon, Sep 23, 2019 at 01:15 PM, david mugridge wrote:

The 1KHz peaks are still there

The source may be DC-DC convertor. Try to disconnect external power from NanoVNA, is it still present?

I think noise may come from DC-DC converter used in battery charger. Because there is noticeable higher noise when external power supply is connected and this noise is not come through cable. It is missing when there is no external voltage.

On Mon, Sep 23, 2019 at 03:06 AM, david mugridge wrote:

The nanovna has a very strong 1KHz component - probably a result of the
1KHz codec frame-rate.

I opened the nanoVNA and connected the line in of a good USB audio device to the reference SA612. But as I did not dare to do two connections the unbalanced signal had a lot of noise. And there were 1kHz peaks independent from the selected output frequency, possibly coming from the PC itself as connecting the audio input to the ground of the nanoVNA gave the same noise.
Looking with a scope showed a very clean triangular 5kHz signal, although with some jitter that might explain some of the disturbances we see.
As disconnecting the USB resets the nanoVNA U was not able to measure with disconnected USB as I do not know how to stop the sweep (e.g.the writing to the SI5351) from the UI

Hello,

Allow us, please, to point out that to be
possible to the slightest a comparison
between measurements regarding
nanovna and/or vna, these measurements
should be accompanied by an estimation
of their uncertainty, as well as by a clearly
stated way of its calculation.

Sincerely,

yin@pez@arg

4

On Mon, Sep 23, 2019 at 07:34 AM, sala nimi wrote:

ADL5920

does only scalar measurements

...and when it's dainty, black and lacy, it is even more dangerous!

John

at radio station VE7AOV

+++++


On 2019-09-23 7:03 a.m., Bear Albrecht wrote:

Caution is the keyword.
FWIW I heard long ago that nylon underwear can generate 3000 volts.

Bear Albrecht W5VZB New Mexico

--

Ouch!

Bear Burt, K6OQK

--
Sent from my Android thingamabob with K-9 Mail. Please pardon the spelling errors as the dog can't spell so good.

Analog devices has a bridge and detector IC ADL5920, is this useful. It goes from 9kHz to 7GHz.

Caution is the keyword.
FWIW I heard long ago that nylon underwear can generate 3000 volts.

Bear Albrecht W5VZB New Mexico

Bruce,
This link might interest you, . It describes a fixture and procedure for measuring ferrite beads using the DG8SAQ VNWA. I believe over their joint frequency range, measurements between the DG8SAQ and nanoVNA have shown close correlation.

On Mon, Sep 23, 2019 at 12:18 AM, Jeffrey Vandenbroucke wrote:

Coil coax around a ferrite and connect the outer shield for a S21 measurement.
Loss in S21 = choking :

Just so I understand, would I connect only the outer shield to the center pin of the two ports, leaving the center of the coax floating unconnected?

These peaks are from spurs of the SI5351 output so they move with the IF frequency and happen at 1kHz intervals.
You see them (although lower) also for the 8kHz and 12kHz harmonics of the IF
The lower the output frequency, the lower these spurs (I hope)
The temperature of the SI5351 is also expected to have an impact

Hi Alan,
the measurements lower limit is given by the phase noise of the SAs oscillators. HP Application Note 270-2 "Autometed Noise Sideband Measurements using the HP 8568A Spectrum Analyzer" shows that typical phase noise is -110dBc/Hz between 500Hz to abt. 100kHz. So my rubidium standard is probably better than this.
You can only get reasonable results if PN of the device to be measured is worse than the analyzers own PN. There are much better ($$$$$$$) specialized PN measurement systems available now, going down to -180dBc/Hz.
Ernst

Erik,

I re-ran it at 1.2GHz, which will correspond to 240MHz. I also changed the
offset to 4KHz. Here are the results:

[image: image.png]

The 1KHz peaks are still there (and unrelated to the IF frequency). It
would be preferable that they weren't there, but we're only interested in
the peak at the IF frequency, so can we just ignore them?

Rgds,
Dave

For your reference here are the FFT's of the audio signal from CH1 while
connected to CH0 at various frequencies. 50 MHz, 299MHz, 1200MHz and
2100MHz, all with offset of 4kHz
Next the isolation measurements for 50MHz and 2100MHz.
This is done in my own HW so there are no changes in ADC settings, apart
from the SI5351 everything else remains the same.
With strong signals the noise floor increases max 10dB but the SNR
differences are as expected due to decrease in the 4kHz harmonic mixing
signal.
As you can see FFT'2 are rather clean. Only the 4kHz and its harmonics.
Close observation of the 4kHz shows its starts to wobble more at higher
frequencies explaining why it does not fit perfectly in the 480 samples you
use.
Hope you will be able to see the same once you have done the windowing of
the FFT input signal.

Erik,

I've separately emailed my results having added windowing to the FFT
signal. While my results are much improved from previously, the noise
spectrum is nowhere near as clean as yours. I'm assuming that although the
front-end of your setup is like the nanovna, the audio backend is different
and that you don't use the TLV3220 for ADC (your sample rate is > 200KHz?).
The nanovna has a very strong 1KHz component - probably a result of the
1KHz codec frame-rate. The CPU does a lot of processing each frame which
might be injecting noise.

Your observation of slight 4KHz wobble is a worry in that it might force
the need for a windowing function on larger samples.

Rgds,
Dave

I tested windowing and that does not make a big difference as can be expected in this case where the stimulus is fully controlled
What is worrying me are the multiple peaks you get 1kHz apart next to the 5kHz.
Some SI5351 have difficulty locking above 250MHz (the official maximum output frequency) and your 1.29Ghz would use a 258MHz signal from one of the SI5351 outputs.
The 1kHz pattern is identical to what I sometimes see, but for me its closer to 300MHz and not always.
So the 1kHz peaks are not noise but an artefact of a SI5351 having difficulty to output the required signal.
There is already a firmware that limits the maximum fundamental to 250MHz to avoid this problem.