[time-nuts] VNA Project

Kmec at aol.com Kmec at aol.com
Mon Jun 2 13:58:14 EDT 2014


Hello!
Most of the time I do not anything of significance to contribute, but VNA's 
 are near & dear to me. I currently have a grad student working on a poor  
mans VNA that will go to 2700 MHz. The issue is phase measurement over that  
range, which, even though there are a bunch of chips that purport to do 
this,  not really. So a synthesized tracking dual channel super het system is  
needed to measure phase over 0-360 degrees, where the phase component of the 
 vector is measured at a fixed frequency, comparing the reference to the 
test  channel.  A good starting place for understanding is the manual for the  
HP8410A/B/C VNA from the '80's, available online at Agilent. It will 
explain  many of the issue and provide a block diagram that you can modify with 
modern  components. Two synthesizers (or a dual with IF offset on one) are 
probably the  best way for the stimulus & receiver LO.
 
73
Jeff Kruth
WA3ZKR
 
 
In a message dated 6/2/2014 12:00:28 P.M. Eastern Daylight Time,  
time-nuts-request at febo.com writes:

Message:  1
Date: Mon, 2 Jun 2014 16:43:12 +0200
From: Attila Kinali  <attila at kinali.ch>
To: time-nuts at febo.com
Subject: [time-nuts] VNA  design
Message-ID:  <20140602164312.66b92049910fcab6c8aa893b at kinali.ch>
Content-Type:  text/plain; charset=US-ASCII

Hi,

I know this is not exactly a  time-nut question, but i guess this is
the best place i know to ask about  this stuff.

I recently got introduced into the usefullness of a VNA.  But these
things are horribly expensive for home use, even if bought from  ebay
(before you say anything, remember i live in europe, where  every
boat anchor hast to travel a long way). But given that most of  the
designs that are on ebay are from the 80s and early 90s, i thought  that
with todays ICs it should be easy to come up with a design that  does
the same thing but can be build on a kitchen table.

Well, my  problem now is, that i don't know how to build a VNA.
Yes, i understand the  basic principle. I can come up with a design
that should work. But i have  no clue about any problems or difficulties
in building these devices. Ie  it's very likely that i fall into a dozen
traps when i try to build  one.

I tried to get information on how to build a VNA, or what kind of  trouble
people had operating one, but beside the VNA book[1] Rick mentioned  a 
couple
of months ago and ko4bb's site (thanks man! your manual collection  is a 
gold
mine!), my searches came out blank. As i'm quite sure that there  is
information of that kind out there, i would like to ask whether  someone
could point me to some documents, webpages, books, papers, etc that  would
show me the detailed design of VNA, the problems people had with  some
designs or anything else that would be of interest in such an  endavor.


Also, any good resource on how to build a directional  coupler that
does 10-3000MHz without going to exotic materials would be  much
appreciated. All papers i found deal mostly with stuff above  5GHz.
Seems like "low frequency" couplers are considered "a solved  problem".


Attila  Kinali

[1] Handbook of Microwave Component Measurements: with Advanced  VNA 
Techniques
by Dunsmore,  2012




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