Re: Narrow band filters and LO phase noise/jitter?
Another video nice video explaining RBW is this one
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Re: Narrow band filters and LO phase noise/jitter?
What does RBW stand for Resolution bandwidth. This video [1:50/5:14] uses an example of a 300 Hz RBW to resolved equal amplitude signals separated by 1 kHz: and is it the same as IF BW ? Nope. Traditional analyzers with non-baseband IF scan wider bands mixed down to some intermediate frequency, so IF BW must be wide enough to pass all signals to be subsequently resolved.
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Re: Narrow band filters and LO phase noise/jitter?
The IF BW is " intermediate frequency bandwidth" What does RBW stand for and is it the same as IF BW ?
Thanks in advance
Greg
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-----Original Message----- From: [email protected] < [email protected]> On Behalf Of alan victor via Groups.Io Sent: 10 July 2019 19:42 To: [email protected]Subject: Re: [nanovna-users] Narrow band filters and LO phase noise/jitter? 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?
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Re: Narrow band filters and LO phase noise/jitter?
My last message was meant in response to Oristo. Forgot to quote it.
"Use of 74LVC4066 Quad bilateral switch instead of SA612 mixer is elegant;
given square wave Si5351 output, its ideal mixer becomes a switch...
That would be a nice upgrade for nanoVNA2 (picoVNA?)"
It might also be better to redesign the resistance bridge for wider impedance measurement.
Current balanced 50 ohm bridge, NanoVNA design, does not have wide range. The FA-VA5 and EU-1KY antenna analyzers
have different front end designs. The FA-VA5 has a reasonable measurement range of 5 to 1000 ohms, far better than NanoVNA.
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Re: Narrow band filters and LO phase noise/jitter?
It might also be better to redesign the resistance bridge for wider impedance measurement.
Current balanced 50 ohm bridge, NanoVNA design, does not have wide range. The FA-VA5 and EU-1KY antenna analyzers
have different front end designs. The FA-VA5 has a reasonable measurement range of 5 to 1000 ohms, far better than NanoVNA.
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Re: Narrow band filters and LO phase noise/jitter?
I would think that just putting resistors in series with each side of the crystal would raise the impedance enough to unload the Q. I would start with 1 K ohm on each side (for the series measurement), and see if it narrows the response. Of course this comes at the expense of increasing the attenuation of the DUT.
Stuart K6YAZ
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-----Original Message----- From: alan victor <avictor73@...> To: nanovna-users < [email protected]> Sent: Wed, Jul 10, 2019 5:02 pm Subject: Re: [nanovna-users] Narrow band filters and LO phase noise/jitter? A thought experiment and an issue with comparison of the single crystal with the matched filter counterpart. A single crystal in series mode is embedded in a 50 ohm system, in this measurement. Essentially, operating with a doubly loaded Q. If this de-Q effect is significant, the issue we are trying to address may not show itself. We really would like to transform the VNA source and load in affect to an impedance level that would operate the xtal as close as possible to its unloaded Q value. Of course, NOT a straight forward task.
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Re: Narrow band filters and LO phase noise/jitter?
Yes, because of the strong impedance mismatch between the crystal and the VNA there may be some passband ripple.
But it is still instructive to see what the passband curve looks like with closely scanned/calibrated NanoVNA.
I'll leave the impedance matching problem to you. Maybe APLAC simulation will help.
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Re: Narrow band filters and LO phase noise/jitter?
A thought experiment and an issue with comparison of the single crystal with the matched filter counterpart. A single crystal in series mode is embedded in a 50 ohm system, in this measurement. Essentially, operating with a doubly loaded Q. If this de-Q effect is significant, the issue we are trying to address may not show itself. We really would like to transform the VNA source and load in affect to an impedance level that would operate the xtal as close as possible to its unloaded Q value. Of course, NOT a straight forward task.
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Re: Narrow band filters and LO phase noise/jitter?
Thanks, George, for the FA-VA5 video hyperlink:
Use of 74LVC4066 Quad bilateral switch instead of SA612 mixer is elegant;
given square wave Si5351 output, its ideal mixer becomes a switch...
That would be a nice upgrade for nanoVNA2 (picoVNA?)
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Re: Narrow band filters and LO phase noise/jitter?
Here is some information on phase noise on the chip, Si5351A used in the VNA.
It is reasonable, nothing extraordinary, however, the loop configured in the VNA may do some noise correction. In any case, I'll look at a crystal. If that plays out and the required resolution is quite small, it may imply that the span I must use is much less than what I currently selected.
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Re: Narrow band filters and LO phase noise/jitter?
Sure, I'll try that. I'll try an xtal in its shunt mode, so just a S11 measurement. Then in series mode in which case I should pick up both a S11 and S21 set of values. I assume you measured the xtal in its series mode. ________________________________ From: [email protected] < [email protected]> on behalf of George <steber@...> Sent: Wednesday, July 10, 2019 10:34 PM To: [email protected]Subject: Re: [nanovna-users] Narrow band filters and LO phase noise/jitter? Now try a single crystal, closely scanned/calibrated, near resonant frequency point. It won't be matched to 50 ohms but will still give you a narrow curve. I tried a crystal at 27 MHz and it looked good, without all the noise of your 500 Hz filter. Next, I plotted Zmag and Zang too from S11 values and it didn't look too bad either. But don't count on correct impedance values when you are too far from 50 ohm sweet spot.
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Re: Measurement of output signal
Thanks for info, George. Thats what I was looking for.
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Re: Measurement of output signal
Sorry, but gave you wrong reference date for QEX article.
It is titled "DG5MK IV Meter, An Accurate Antenna Analyzer" by Michael Knitter in the May, 2017 issue of QEX.
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Re: Narrow band filters and LO phase noise/jitter?
Now try a single crystal, closely scanned/calibrated, near resonant frequency point.
It won't be matched to 50 ohms but will still give you a narrow curve.
I tried a crystal at 27 MHz and it looked good, without all the noise of your 500 Hz filter.
Next, I plotted Zmag and Zang too from S11 values and it didn't look too bad either.
But don't count on correct impedance values when you are too far from 50 ohm sweet spot.
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Re: Measurement of output signal
"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.
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Re: Measurement of output signal
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?
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Re: Measurement of output signal
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.
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Re: Measurement of output signal
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.
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Re: Narrow band filters and LO phase noise/jitter?
Here are some plots/data capture.
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Oristo
Nuno
