[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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