开云体育

"You are right. But frankly speaking I do not understand why the spurious do not influence the test results. I am lacking the theory behind."

If the system is linear, the harmonics can be separated and filtered out. Usually with DSP processing.

But if the harmonics start to enter nonlinear region of component, mixer for example, filtering does not work completely.

One of your countrymen, Michael Knitter has an English-language presentation where he describes, in detail, how the harmonics are handled internally by the FA-VA5 antenna analyzer that he designed. It should answer you questions. He also wrote a article for QEX magazine, July, 2015, where more of the math is shown.

BTW the images attached are so compressed that often it is very hard to read any text. Can this be modified by the moderator of the group?

Just by curiosity I made a phase noise measurement of the output signal. For comparison the overlay in the picture is my 10MHz rubidium standard which shows the measurement limits of my system.

You are right. But frankly speaking I do not understand why the spurious do not influence the test results. I am lacking the theory behind.

Here are some plots/data capture.

All good questions and point. Thanks.

I shall post my measurement plots. I did both data capture as well as photo shot of the VNA as it looks a bit better on the VNA screen as opposed to the data capture.

I did a calibration span from 453-457 kHz. So with 101 points that should be ~ 40 Hz step and should resolve the filter BW fairly well. And in fact with 2 markers on, marker 2 will read DELTA Frequency in relation to marker 1. Nice feature. And you can discern a filter BW of ~ 400 Hz.

However, there is most definite what I will call phase modulation as there are distinct sidebands along the lower and upper skirts of the filter. Is the LO phase noise sufficiently low that with (assuming) 40 Hz steps this phase modulation of the skirts should not be present? Need to go look at their LO spec. Or is the interpolation challenged? Any form of averaging would certainly help.

Alan

________________________________
From: [email protected] <[email protected]> on behalf of amirb <amir.borji@...>
Sent: Wednesday, July 10, 2019 7:28 PM
To: [email protected]
Subject: Re: [nanovna-users] Narrow band filters and LO phase noise/jitter?

I may be wrong, but:
* is nanoVNA not derived from the EU1KY antenna analyzer?

No, EU1KY is quite a bit different

* in which case, mixers basically mix down to DC (no IF)
- bandwidth limited by RC networks into ADCs with 5.5 MHz gain bandwidth (at
100 kHz)

in any case, you have a limited resolution bandwidth even if it is not apparent as a physical filter circuit.
although I think there must be a lowpass filter after the mixer (zero IF)
The question is how wide/narrow is it?

On Wed, Jul 10, 2019 at 2:57 PM amirb <amir.borji@...> wrote:

certainly they are not implementing a narrow FFT bandwidth filter in the DSP

"DSP math libraries provided by ARM, with FFT code highly optimized for speed"

I didn't get where this quote is coming from but it does not mean the NanoVNA designer has
implemented a narrow band low pass filter (resolution BW) in DSP for small spans. Maybe he can explain it...

I may be wrong, but:
* is nanoVNA not derived from the EU1KY antenna analyzer?

No, EU1KY is quite a bit different

* in which case, mixers basically mix down to DC (no IF)
- bandwidth limited by RC networks into ADCs with 5.5 MHz gain bandwidth (at
100 kHz)

in any case, you have a limited resolution bandwidth even if it is not apparent as a physical filter circuit.
although I think there must be a lowpass filter after the mixer (zero IF)
The question is how wide/narrow is it?

On Wed, Jul 10, 2019 at 2:57 PM amirb <amir.borji@...> wrote:

certainly they are not implementing a narrow FFT bandwidth filter in the DSP

"DSP math libraries provided by ARM, with FFT code highly optimized for speed"

I didn't get where this quote is coming from but it does not mean the NanoVNA designer has
implemented a narrow band low pass filter (resolution BW) in DSP for small spans. Maybe he can explain it...

He is implementing a narrow bandwidth filter in the DSP to remove artifacts of the square wave.

It is the same procedure used by the FA-VA5 and EU-1KY antenna analyzers. Otherwise the square wave would be a big problem.
But using SA612 mixers could be a problem if they are driven into nonlinearity by all the harmonics involved.
For this reason, the FA-VA5 eschewed the SA612 in favor of a more linear mixer.

Michael Knitter has an English-language presentation where he describes, in detail, how the harmonics are handled internally by the FA-VA5.

I may be wrong, but:
* is nanoVNA not derived from the EU1KY antenna analyzer?
* in which case, mixers basically mix down to DC (no IF)
- bandwidth limited by RC networks into ADCs with 5.5 MHz gain bandwidth (at 100 kHz)

On Wed, Jul 10, 2019 at 2:57 PM amirb <amir.borji@...> wrote:

certainly they are not implementing a narrow FFT bandwidth filter in the DSP

"DSP math libraries provided by ARM, with FFT code highly optimized for speed"

in this instrument with a very simple schematics (although I don't have it in front of me and vaguely remember the general picture of it) I don't remember
seeing any type of variable filter or filter bank in RF stage. It must be just a simple fixed BW filter for the whole sweep range

certainly they are not implementing a narrow FFT bandwidth filter in the DSP (as some modern spectrum analyzers do for <10Hz RBW)
therefore, I am sure there is a fixed RBW filter in IF stage. if you have the schematics you should be able to figure it out.

Excellent point. Is there a tag between the analyzer sweep range and its resolution BW? I should do a cal over a reasonable narrow frequency range and see if this helps the situation. Otherwise it may very well be RBW limited.

________________________________
From: [email protected] <[email protected]> on behalf of amirb <amir.borji@...>
Sent: Wednesday, July 10, 2019 4:15 PM
To: [email protected]
Subject: Re: [nanovna-users] Narrow band filters and LO phase noise/jitter?

it's not that surprising, I think, considering that the RBW (or IF BW) of this instrument is definitely not
narrow enough to give you the resolution required for like a 1KHz or perhaps even 5KHz span. of course number of sample points is another bottleneck
but not as critical as the RBW.
Does anybody know what the RBW actually is?

it's not that surprising, I think, considering that the RBW (or IF BW) of this instrument is definitely not
narrow enough to give you the resolution required for like a 1KHz or perhaps even 5KHz span. of course number of sample points is another bottleneck
but not as critical as the RBW.
Does anybody know what the RBW actually is?

So ... I have played a little more ... Thanks to Larry for listing the serial commands ... I can now command my nanoVNA from ubnuntu using them .. and after a play and putting putty on the same virutal drive in PlayOnLinux have been able to confimr that simply linking the comport through works ..

ln -s /dev/ttyACM0 ~/PlayOnLinux\'s\ virtual\ drives/'NanoVNA'/dosdevices/com*

where * is whatever com port you wish to use and NanoVNA is the name of your Virtual Drive.

Putty will connect and work :) however NanoVNA Sharp still refuses to connect :(

More fun ... if anyone whishes me to try other software yell ... also getting POL to run the nanovnasharp program was a little fun ... when setting up the virtual drive you need to remove mono completely and then add the dotnet40 or above component .. if the mono compoent is still installed they clash and crash :(

Cheers

Tim M0THM

I started looking at some narrow band mechanical filters.
The measurement was challenged to look at a 500 Hz wide 455 kHz filter.
I will double check if the limits are 101 data points/interpolation or simply LO jitter.
It was very difficult to discern the transition skirt band.

However, other somewhat wider mechanical filters worked out well as shown here.
A 88 kHz sideband filter and a classic 455 kHz filter from a Collins. These were both
headed to the land fill. Such a shame. Here old meets new! Alan

I use an old blackberry 800mA charger.
Grab the datasheet for the IP5303 charger chip that's used for more info.
(Chinese)
1.2A Charging
1.0A Discharge

Thanks, I was wondering about the charger . It will at least charge a 800ma
Thanks

Frank - do a search though the forum and you'll find all kinds of useful info that others have already supplied...

Have a look at my posts & photos - I stuck an old Motorola 800mAH cellphone batt on mine - no probs.

...Larry

Does anyone know how big a battery in mAh (charging wise) the unit can handle?
Frank

Is anyone interested in an extended back cover for the NanoVNA? I designed and printed a sample it has a 6mm deep "pocket" that is 71mm X 40mm. Should be big enough to double sided tape a bigger battery in it

1

2

3

Frank
ka2fwc@...

I just ordered 1 from Banggood preorder, I hope this is the correct one to make sure Huegen gets paid for his work