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 Post subject: SNA vs VNA
PostPosted: Nov Tue 28, 2017 10:32 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
I'd like to upscale my RF analyzing capability. I have an older Agilent E4411B and an almost new Rigol spectrum analyzer. I've used both for checking high, low, and bandpass filters. I probably haven't come near using the capabilities of either. That said, as a certified HP test equipment junkie that hasn't bought anything in a few years I've started looking in to picking up and SNA (HP8757A) or VNA (HP8753A).

For about the same cost as the HP8752A and much smaller footprint, I can get this VNA: https://www.arraysolutions.com/vna-2180
but it doesn't cover the full Ham band ranges (LF to microwave).

This isn't a "need thing" because at this point I don't fully understand the difference or what I can do with either that I can't do with a SA. That makes it a "want thing" so the old adage - If you don't know what it does then you don't need it, doesn't apply :mrgreen:

I could probably find a good explanation on the net but I trust this place (note that it's not a website, it's a place... a community if you will) and the people that come here to give me good, honest answers.

The other question that I suppose should be asked is- If I just have to have boat anchor sized SNA or VNA is there a better model than what I have listed?

Thank you in advance

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 Post subject: Re: SNA vs VNA
PostPosted: Nov Tue 28, 2017 11:47 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 7199
Location: Long Island
A scalar network analyzer (SNA) gives you a display of amplitude vs. frequency so you can measure the insertion loss of cables and components at RF frequencies. It is basically a signal generator, test fixture or port, and a detector/receiver of some type connected to an indicator (meter or CRT display). The device or system to be measured is connected to the fixture which applies RF from the generator (the fixture usually also provides a reference signal to the receiver and an automatic level control signal back to the generator), and connects the output of the DUT to the detector/receiver. As the generator frequency is swept, the insertion loss of the device under test is measured. With the availability of low cost digital spectrum analyzers with tracking generator outputs, scalar network analyzers have pretty much fallen by the wayside.

A vector network analyzer (VNA) is similar but in addition to amplitude vs. frequency it gives you phase information as well. This is obviously a lot more useful from an RF engineering perspective but it is a more complicated and expensive instrument. Most network analyzers being manufactured today are of this type. Modern ones have all sorts of fancy bells and whistles allowing you to automatically make all sorts of fancy tests like noise figure, display Smith charts, convert measurements into S-parameters, etc.

One bit of advice: many of the older SNAs and VNAs actually consisted of multiple sections that would be connected together in a rack to make a complete system. If you don't get all the units, then parts is parts. Many network analyzers require external detector probes or modules which are seldom found with the main units and can be very expensive when they do turn up. Read as much as you can about any prospective purchase with an eye towards what else you are going to need--detectors, special cables, modules, plug-ins, manuals, or discrete units--to make it work.

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 Post subject: Re: SNA vs VNA
PostPosted: Nov Wed 29, 2017 12:11 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Thanks Chris. Both of my SA's have tracking generators and one has a module for reading VSWR so that puts the SNA out of the picture.

I noticed some of the older SNA and VNA's had add ons. That's kind of what prompted the post. I recently saw some nice filter characteristic plots from the VNA that I linked to. It requires software an a PC and for my infrequent needs (or wants) it might do. The old HP gear is prettier :)

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It's hard to solve an equation if every term is an unknown.

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Mike


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 Post subject: Re: SNA vs VNA
PostPosted: Nov Wed 29, 2017 2:20 am 
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Joined: Nov Mon 02, 2009 7:01 am
Posts: 2311
Location: Lincoln City, OR
Greetings to Mike and the Forum:

Beware the 8753A.... or any other 4 port box. You need a fancy detector/hybrid box to turn the 4-port analyzer into a 2-port device, which is what you really need for most measurements. As Chris points out, this rarely comes with the analyzer.... although one current eBay listing (for about $1,800) does show the gadget in the photo, so it may be included.

The HP box you want is the 8712. Granted, it only goes to 1.3 GHz, but it is easy to use, works fantastically well and it is a 2-port device, so it is ready to go with no external accessories.

As far as the Array Solutions gadget is concerned, if you do some shopping on the internet, you can find a similar VNA in kit form that has much greater frequency coverage and is half the price.

I'd love to have an HP 8712, but I ain't made of money, so I get by with the Ten-Tec box (invented by the TAPR group and sold to Ten-Tec; now out of production). It only goes to 100 MHz or so, but it works very well within that range. I shelled out about $600 for it some years ago before VNA kits became available. My personal opinion is that the Array Solutions box is way over-priced. Just my $.02 worth; your mileage may vary.

Regards,

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 Post subject: Re: SNA vs VNA
PostPosted: Nov Wed 29, 2017 3:27 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Thanks Jim, all great info. My watchlist just got shorter. I'll look around for other VNA kits. Maybe Array Solutions is pricing against the used market?

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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 Post subject: Re: SNA vs VNA
PostPosted: Nov Wed 29, 2017 3:53 am 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 815
Location: Santa Rosa, CA
Mike,
I was an engineer at HP where many of the S & VNA's you mentioned
were designed and built. Was involved in many directly or indirectly.

First of all a VNA is a much more powerful instrument than a SNA
like the HP8755/6/7 series. However the *raw* performance of
these SNA's (with the right bridge or detector) can be very impressive.

Having phase information (VNA) allows you to plot a Smith
chart which makes conjugate matching a snap. Markers on
the Smith charts allow you to view the complex impedance at
any point which can be useful when designing filters, amps or
even oscillators (DRO's). I can fill pages about other advantages
but don't want anyone falling asleep....

VNA's I'd suggest for casual use, in order;
HP 8712 (1.3 GHz) or HP 8714 (3 GHz); 8711 and 8713 were SNA's
HP 8753 (any version) but be sure to get the test set AND
freq doubler that goes to 6 GHz....this is a top notch box
HP 8505, older design and bigger but very nice specs, pre-software
correction though....should be cheapest
HP 8720 (20 to 40 GHz) VERY nice, modern instrument, expensive
HP 8510 (to 50 GHz), I was on this project, metrology grade
performance but 4 boxes required...only for the fanatics and wealthy
HP 8754, much older, all analog but very useful, need seperate test set
HP 8410, the great grand daddy, some were run with an HP1000
mini-computer, a full rack, slow as molassa but got the job done

I currently have, or have owned most of these and use them in
my personal shop. My go-to VNAs are HP8714B, 8753C,
and 8720C.

If you have detailed questions , feel free to send a PM.
Steve


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 Post subject: Re: SNA vs VNA
PostPosted: Nov Wed 29, 2017 4:55 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 31399
Location: Maryland 20709, USA
Somewhat Noisy Amplifier vs. Very Noisy Amplifier ? ? ?

It's always wise to present full names before acronyms.

- Leigh

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: SNA vs VNA
PostPosted: Nov Wed 29, 2017 5:10 am 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
Chris covered it in his reply :lol:

SNA - Scalar Network Analyzer
VNA - Vector Network Analyzer

That sums up everything I knew before posting the question :D

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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 Profile  
 
 Post subject: Re: SNA vs VNA
PostPosted: Nov Wed 29, 2017 5:16 am 
Member

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 1916
Location: Weimar, Texas
zarco wrote:
Mike,
I was an engineer at HP where many of the S & VNA's you mentioned
were designed and built. Was involved in many directly or indirectly.

First of all a VNA is a much more powerful instrument than a SNA
like the HP8755/6/7 series. However the *raw* performance of
these SNA's (with the right bridge or detector) can be very impressive.

Having phase information (VNA) allows you to plot a Smith
chart which makes conjugate matching a snap. Markers on
the Smith charts allow you to view the complex impedance at
any point which can be useful when designing filters, amps or
even oscillators (DRO's). I can fill pages about other advantages
but don't want anyone falling asleep....

VNA's I'd suggest for casual use, in order;
HP 8712 (1.3 GHz) or HP 8714 (3 GHz); 8711 and 8713 were SNA's
HP 8753 (any version) but be sure to get the test set AND
freq doubler that goes to 6 GHz....this is a top notch box
HP 8505, older design and bigger but very nice specs, pre-software
correction though....should be cheapest
HP 8720 (20 to 40 GHz) VERY nice, modern instrument, expensive
HP 8510 (to 50 GHz), I was on this project, metrology grade
performance but 4 boxes required...only for the fanatics and wealthy
HP 8754, much older, all analog but very useful, need seperate test set
HP 8410, the great grand daddy, some were run with an HP1000
mini-computer, a full rack, slow as molassa but got the job done

I currently have, or have owned most of these and use them in
my personal shop. My go-to VNAs are HP8714B, 8753C,
and 8720C.

If you have detailed questions , feel free to send a PM.
Steve


Thanks Steve! I'll do some research and if I have some questions I'll PM you.

_________________
It's hard to solve an equation if every term is an unknown.

73
NE5U

Mike


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 Profile  
 
 Post subject: Re: SNA vs VNA
PostPosted: Nov Wed 29, 2017 6:46 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 31399
Location: Maryland 20709, USA
Mike6158 wrote:
Chris covered it in his reply :lol:

SNA - Scalar Network Analyzer
VNA - Vector Network Analyzer

That sums up everything I knew before posting the question :D

It would be nice if you'd present that information to potential readers WHEN posting the question.

- Leigh

_________________
73 de Leigh W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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