[time-nuts] VNA design

[Attila Kinali]

On Mon, 2 Jun 2014 11:09:55 -0400
Scott McGrath <scmcgrath at gmail.com> wrote:

> You might want to look at the N2PK and DG8SAQ vector network analyzer
> projects there are also some commercial USB based 'personal' network
> analyzers out there starting about 6K 

I've seen both and looked at their implementation. Especially DG8SAQ is
conceptually quite interesting IMHO (using the harmonics of an DDS chip).
But i'd like to get at least to 1.6GHz (think GPS) Otherwise i would have
ordered one of them already.

(Side note: i am not sure whether i will get to building a VNA. I am
currently just playing with the idea and try to learn about their function
as much as possible)

> 
> As for directional couplers. I would suggest buying vs building Mini
> Circuits has a line of high quality inexpensive couplers in both coaxial
> and surface mount at price points affordable for individuals these really
> are a solved problem.   

Yes. But their SMD are only 3 port, ie the isolated port is internally
terminated. Which in turn means, i'd need to put two of those in to get
both transmitted and reflected wave.

> 
> You could of course build waveguide based Couplers at lower frequencies they
> would be physically large but easy to construct if you have access to
> machine tools

I think all the Minicircuit ones are build using transformers. I cannot
think of any other way to get such a large bandwith in these small dimensions
otherwise.


				Attila Kinali

-- 
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