Author Topic: Best VNA for around or under $2000?  (Read 10089 times)

0 Members and 1 Guest are viewing this topic.

Offline mark432

  • Newbie
  • Posts: 9
  • Country: us
Re: Best VNA for around or under $2000?
« Reply #100 on: December 07, 2024, 06:47:30 am »
Does LiteVNA64 actually allow you to define cal standards?

From looking at the manual it seems that it just assumes the SOLT are perfect devices.
This seems a bit bonkers to me for something that is going up to 6 GHz.

I doubt that the short and open standards they provide line up perfectly with the reference plane.  You would think you could at least set the parameters of the thru.
But the even bigger point is cables/adapters.  Sometimes you need to measure things at the other end of cables and adapters. 

I have a regular nanoVNA, and I didn't worry much about it because of lower frequency limit.

I suppose you just have to measure a reference standard and then correct your data after the fact.
Still, I wonder what the phase error after calibration is.

Regarding the LibreVNA.  I see that an electronic calibration module is hitting the market.  I wonder why they made it a 4 port cal module, when the only librevnas I can find are 2 port?
Is there a 4 port model in the works?  I doubt it, but I would love a dual-source 4 port LibreVNA.
 

Offline knudch

  • Regular Contributor
  • *
  • Posts: 77
  • Country: dk
Re: Best VNA for around or under $2000?
« Reply #101 on: December 07, 2024, 02:21:54 pm »
You can do 4 port by using 2 LibreVNA
Supported in SW, called compound device

As understand it, 4 port can be done with 2 of shelf LibreVNA
8 if you some additional PCB's

But you will not have phase information between each unit...as I understand it

Have never tried it as I don't have 2 LibreVNA's

There also something called Mixed Mode....please read the support mail list or ask the designer

Knud
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 12280
  • Country: us
Re: Best VNA for around or under $2000?
« Reply #102 on: December 08, 2024, 12:04:48 am »
Does LiteVNA64 actually allow you to define cal standards?

Going thought the menus of a fairly recent version of firmware,  it does not appear to.

From looking at the manual it seems that it just assumes the SOLT are perfect devices.
This seems a bit bonkers to me for something that is going up to 6 GHz.

Well, it was designed for a certain price.   I am not sure if the hardware has enough resources to support it (code space, processing power...).       

I doubt that the short and open standards they provide line up perfectly with the reference plane.  You would think you could at least set the parameters of the thru.
But the even bigger point is cables/adapters.  Sometimes you need to measure things at the other end of cables and adapters. 

Bigger point?  Normally I would cal these out.   I normally have cables attached and measure on the other end. 

I have a regular nanoVNA, and I didn't worry much about it because of lower frequency limit.

I suppose you just have to measure a reference standard and then correct your data after the fact.
Still, I wonder what the phase error after calibration is.

Like how the LibreVNA requires a PC,  if you want to perform more advanced math with the LiteVNA, you also would need a PC.   

***
Same for any of these low cost VNAs, not just the LiteVNA. 

***
Link showing LiteVNA HW rev 3.2 + PC + Solver to perform T-Check (after sorting out a few problems).  The only way to get that level of performance was to characterize the cheap standards and enter that data into Solver.   The LiteVNA is the limiting factor, not the standards. 
   
https://www.eevblog.com/forum/rf-microwave/nanovna-custom-software/msg5685217/#msg5685217

Someone had attempted a similar test using the LibreVNA and I think they achieved 3GHz.  Similar the the 4GHz I saw with the LiteVNA.
« Last Edit: December 08, 2024, 03:04:00 pm by joeqsmith »
 
The following users thanked this post: mark432

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 12280
  • Country: us
Re: Best VNA for around or under $2000?
« Reply #103 on: December 08, 2024, 08:49:00 pm »
I put together some quick software to try out that old Weinschel 63dB step attenuator and all of the stages are fine.

Using an IFBW of 500Hz, I stepped from 0 to 60dB, then inserted that 40dB fixed attenuator. 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 12280
  • Country: us
Re: Best VNA for around or under $2000?
« Reply #104 on: December 08, 2024, 11:39:18 pm »
Showing 80, 90 & 100dB with 4kHz IFBW and 1000 averages.   

Offline mark432

  • Newbie
  • Posts: 9
  • Country: us
Re: Best VNA for around or under $2000?
« Reply #105 on: December 10, 2024, 01:10:15 am »
Well, it was designed for a certain price.   I am not sure if the hardware has enough resources to support it (code space, processing power...).       
It's not really a "horsepower" limitation as the calibration only needs to be calculated once when you are doing it.
You're solving for a matrix, that you're going to multiply by your measured data matrix, to give the actual result.
There's definitely more code involved in allowing definable cal sets, but it's all math that you only calculate once at cal.
( I wouldn't expect code space to be a problem these days.)

Once it's done, you're doing the same number of calculations every sweep regardless of the cal type.


Bigger point?  Normally I would cal these out.   I normally have cables attached and measure on the other end. 
Yeah, but often at the other end of your cable you might have other sex or other gender connectors than the supplied cal standards.
Like when measuring at the end of a several foot SMA to N cable.  Best case, you're using a decent adapter than only adds half an inch of phase shift and has a 30 dB RL.
Quite likely you're doing worse.

VNAs are about the best example of "garbage in, garbage out" for test equipment.

I don't see anything else better for the price, but I'm leaning towards LibreVNA if I ever want upgrade from my NanoVNA.
It seems to have much closer to a normal VNA functionality. 
The NanoVNA reminds me more of something like an Anritsu Sitemaster than a full VNA.

I would think the best way to cover cal for super low cost VNAs would be to allow known s-parameter cal for the datasets.
The manufacturer can take 1 minute and measure the standards on a traceable VNA and then provide those files with the standards.  No need to try and make them perfect SOLT.  Just use decent repeatable connectors and stable resistors.

Many of us will have access to a lab-grade VNA and it would be easy to measure a handful of parts as home standards.
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 12280
  • Country: us
Re: Best VNA for around or under $2000?
« Reply #106 on: December 10, 2024, 02:36:55 am »
Well, it was designed for a certain price.   I am not sure if the hardware has enough resources to support it (code space, processing power...).       
It's not really a "horsepower" limitation as the calibration only needs to be calculated once when you are doing it.
You're solving for a matrix, that you're going to multiply by your measured data matrix, to give the actual result.
There's definitely more code involved in allowing definable cal sets, but it's all math that you only calculate once at cal.
( I wouldn't expect code space to be a problem these days.)


Once it's done, you're doing the same number of calculations every sweep regardless of the cal type.

Bigger point?  Normally I would cal these out.   I normally have cables attached and measure on the other end. 
Yeah, but often at the other end of your cable you might have other sex or other gender connectors than the supplied cal standards.
Like when measuring at the end of a several foot SMA to N cable.  Best case, you're using a decent adapter than only adds half an inch of phase shift and has a 30 dB RL.
Quite likely you're doing worse.

VNAs are about the best example of "garbage in, garbage out" for test equipment.

I don't see anything else better for the price, but I'm leaning towards LibreVNA if I ever want upgrade from my NanoVNA.
It seems to have much closer to a normal VNA functionality. 
The NanoVNA reminds me more of something like an Anritsu Sitemaster than a full VNA.

I would think the best way to cover cal for super low cost VNAs would be to allow known s-parameter cal for the datasets.
The manufacturer can take 1 minute and measure the standards on a traceable VNA and then provide those files with the standards.  No need to try and make them perfect SOLT.  Just use decent repeatable connectors and stable resistors.

Many of us will have access to a lab-grade VNA and it would be easy to measure a handful of parts as home standards.

The files I used for the T-Check experiment are 512kB, male only, and limited to 1601 points.  LiteVNA support more points and we would expect to support both M/F.   Trivial for the PC.   

Offline knudch

  • Regular Contributor
  • *
  • Posts: 77
  • Country: dk
Re: Best VNA for around or under $2000?
« Reply #107 on: December 10, 2024, 06:47:32 am »

I would think the best way to cover cal for super low cost VNAs would be to allow known s-parameter cal for the datasets.
The manufacturer can take 1 minute and measure the standards on a traceable VNA and then provide those files with the standards.  No need to try and make them perfect SOLT.  Just use decent repeatable connectors and stable resistors.

Many of us will have access to a lab-grade VNA and it would be easy to measure a handful of parts as home standards.

There is a Guy Kurt Poulsen , search for him in the LibreVNA forum, he has written a article about "transfer" all CAL parametre from a lab-grade to home standards in the LibreVNA.

Knud
 

Offline Miek

  • Regular Contributor
  • *
  • Posts: 91
  • Country: gb
Re: Best VNA for around or under $2000?
« Reply #108 on: December 10, 2024, 12:27:31 pm »
The LiteVNA64 does allow you to define cal standards, it's under Calibrate -> Calibrate -> Calibration Standard. I checked on v1.3.31 and the latest v.1.3.36
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 12280
  • Country: us
Re: Best VNA for around or under $2000?
« Reply #109 on: December 10, 2024, 02:01:07 pm »
The LiteVNA64 does allow you to define cal standards, it's under Calibrate -> Calibrate -> Calibration Standard. I checked on v1.3.31 and the latest v.1.3.36

Nice find.  Mine is much older (07) and appears to at least have some limited settings.   They do not allow a loss term for any of the standards.  The only standard that allows you to define Z0 is the load.    The load also allows an L & C term which at least METAS does not.   It assumes everything is coaxial. 

mark432 suggested ditching the polynomial for the database.  My friends new H4 and the LiteVNA do have that card reader which would easily hold what ever files I would come up with.  May be an option if there was a need for it.

Offline theblinkingman

  • Newbie
  • Posts: 3
  • Country: us
Re: Best VNA for around or under $2000?
« Reply #110 on: December 13, 2024, 05:47:43 am »
I ran a T-check on a LibreVNA and it seems to only make it up to 1.25 GHz under 15%, which doesn't seem that great. 

I used the same T-check on a higher quality VNA and got under +/-4% up to 8 GHz. I used the built in calibration procedure on each, so it's possible something went wrong with that on the LibreVNA. 

Also did a S21 measurement with both ports terminated. 

 

Offline DiSlord

  • Regular Contributor
  • *
  • Posts: 110
  • Country: ru
Re: Best VNA for around or under $2000?
« Reply #111 on: December 21, 2024, 09:21:36 pm »
Quote
Does LiteVNA64 actually allow you to define cal standards?
Yes, LiteVNA allow define calibration standard:
Calibrate->Calibrate->Calibtation standard

Remove Use Ideal flag and define
Open:  Z0, Delay, Offset Loss, C0, C1, C2, C3
Short:  Z0, Delay, Offset Loss, L0, L1, L2, L3
Load: R, Z0, Delay, offset Loss, L, C
Thru: Z0, Delay, Offset Loss

You can change values and in real time see changes

Additional possible save and load standard settings to/from sd card.

PS calibration standard settings equal as on LibreVNA / NanoVNA Saver (NanoVNA saver not use Offset loss settings)
PSS  my tests cheap China calibration kit, define calibration standard settings and improve it
https://groups.io/g/nanovna-beta-test/message/4538
« Last Edit: December 21, 2024, 09:27:43 pm by DiSlord »
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf