Can a VNA replace a tracking generator on a SA?

[ballsystemlord]

Hello,
From what I have read, the tracking gen on a spectrum analyzer allows the SA to perform measurement S21. Is that all? Like, given the choice of using a SA or VNA wouldn't you just go with the VNA? Am I missing something? Is there some feature that the SA+TG can do that a VNA cannot?

Thanks!

[shabaz]

An SA can do things a VNA cannot (and vice-versa). An SA can operate without internally generated stimulus from a tracking generator; i.e., an SA will show what's present solely from its input channel. A VNA requires a locally generated stimulus signal for it to operate.

I suspect you're confusing the term "VNA" with "Spectrum Analyzer with Integrated VNA". Some basic spectrum analyzers come with built-in VNA.

[tautech]

Hello,
From what I have read, the tracking gen on a spectrum analyzer allows the SA to perform measurement S12.

S21 actually. Typo ?

Is that all?

Without a RLB, yes.

Like, given the choice of using a SA or VNA wouldn't you just go with the VNA? Am I missing something? Is there some feature that the SA+TG can do that a VNA cannot?

A few years back and not too long after getting my first SA to explore the black magic field of RF I was in a similar dilemma and all my wishes were answered with the release of the SVA1000X range. SA and VNA in one unit ! 
I've had 2 of these,1.5 and 3.2 GHz and SVA1032X remains one of my all time fav instruments.

[moerm]

Let me put it like this:
There are SAs, often in the form of a base station analyzer or somesuch, who may seem to also have VNA functionality, e.g. by showing a Smith diagram, but very few actually really do.
And there are SAs with a TG who can also serve as a network analyzer - but a scalar network analyzer, not a vector network analyzer. The major difference: the latter also do phase.

If you are in a tight spot and a crude and/or cumbersome measurement is good enough then a VNA may serve as a (somewhat "crippled") SA too. But nowadays with most (halfway modern) scopes doing FFTs, so does a scope.

Hth

[ballsystemlord]

An SA can do things a VNA cannot (and vice-versa). An SA can operate without internally generated stimulus from a tracking generator; i.e., an SA will show what's present solely from its input channel. A VNA requires a locally generated stimulus signal for it to operate.

I suspect you're confusing the term "VNA" with "Spectrum Analyzer with Integrated VNA". Some basic spectrum analyzers come with built-in VNA.

I knew that. I was asking so that I could determine if it was best to buy a SA with a TG, or if the VNA I also intend to get would do the job just fine.
The architectures of the 2 instruments are different. So I was asking because, for all I know, the SA could do stuff with a TG, that a VNA wouldn't otherwise be able to do.

[shabaz]

I knew that. I was asking so that I could determine if it was best to buy a SA with a TG, or if the VNA I also intend to get would do the job just fine.
The architectures of the 2 instruments are different. So I was asking because, for all I know, the SA could do stuff with a TG, that a VNA wouldn't otherwise be able to do.

I cannot read your mind to determine what you already know (and others clearly cannot either from the responses). We simply answered based as best as we could.
 
You didn't mention (in the original post) if the decision was between either an SA+TG, or both SA+TG and a VNA.

I now think you meant to say something something along the lines of:

"If I intend to purchase both a spectrum analyzer instrument and a VNA instrument, should I, in addition, purchase a tracking generator feature? Why would anyone use the SA's TG feature if they also happen to own a VNA?"

If that's what you meant, then there are circumstances where one might prefer to use the SA+TG instead of VNA. For one, unless you've got a very high-end VNA, the dynamic range of the SA is higher. Also with SA+TG you'll be able to see measurements that otherwise might be buried in noise. But they won't be vector measurements. Also, less (and simpler) measurement calibration to do. Plus, some additional features may only be available with the SA and not with the VNA, and there may be differences in sweep speed.

[Bud]

Hello,
From what I have read, the tracking gen on a spectrum analyzer allows the SA to perform measurement S12.

S21 actually. Typo ?

Magnitude |S21| actually. Typo?