VNA design
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
--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
There is a popular DIY VNA designed by N2PK, boards are available from a fellow in Ontario Canada, a quick google search should find the information for you.
Also, Sam Wettlerlin has published much on his web site with respect to Scotty's Spectrum Analyzer project, VNA, return loss bridges, etc.
Also, there is an interesting project called the Poor Hams Scalar Network Analyzer (PHSNA) which may be of interest. There is an active Yahoo group. All that is missing is a phase detector to make it a simple VNA. Based on Arduino and the inexpensive AD9850/AD9851 DDS boards from Asia.
I'd like a VNA too but I am starting small with the PHSNA and will build from there. My needs are not that great, just as a learning tool and to support my ham radio tinkering.
Cheers, Graham ve3gtc
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Attila Kinali
Sent: June-02-14 10:43 AM
To: time-nuts@febo.com
Subject: [time-nuts] VNA design
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
--
The trouble with you, Shev, is you don't say anything until you've saved up a whole truckload of damned heavy brick arguments and then you dump them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin _______________________________________________
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Attila
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
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.
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
Most commercial VNAs are still in the boat anchor class for size and weight at the office we have a R&S 40 Ghz 4 port VNA and it's still huge and heavy along with a fleet of agilents
Sent from my iPad
On Jun 2, 2014, at 10:43 AM, Attila Kinali attila@kinali.ch wrote:
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
--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
There's a DIY project to build a spectrum analyzer at
http://scottyspectrumanalyzer.com . Since it's modular, one version of
the project is to add a couple of modules that change it into a network
analyzer.
If you search ebay for directional couplers, I can almost guarantee that
you will find what you want at a reasonable price.
Ed
On 6/2/2014 8:43 AM, Attila Kinali wrote:
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
Today you can do most of the processing in software. All you need is A/D
and D/A converters that can handle the required bandwidth and get the raw
numbers into the computer. Look up "SDR" type radios and search on the
combination of SDR and VNA and you'll find a few. Then with the same
hardware you have a VNA, spectrum analyzer, oscilloscope, low power
transceiver and so on. This idea is somewhat easy through HF.
On Mon, Jun 2, 2014 at 7:43 AM, Attila Kinali attila@kinali.ch wrote:
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.
--
Chris Albertson
Redondo Beach, California
On 6/2/2014 7:43 AM, Attila Kinali wrote:
Also, any good resource on how to build a directional coupler that
does 10-3000MHz without going to exotic materials would be much
I once had the opportunity to discuss directional couplers with
Julius Botka, then with HP/Agilent. Specifically, a true directional
coupler he designed that approached the range of 10-3000 MHz. IMHO,
Botka was one of the greatest experts of all time in this area.
It took extreme attention to detail to get it to work. It
didn't so much involve exotic materials, but rather expertise.
Don't try this at home kids. Julius said that he designed it before
the era of cheap calibration. Now that everyone has calibration,
you don't need a good directional coupler. You can get away
with a MiniCircuits coupler. But in fact it is
even easier to just use a resistive bridge. Four ordinary
resistors will easily go to 3 GHz. Use a differential amplifier
at the output. Lots of info on this in the literature.
Another way to make in effect a directional coupler is to use
a 180 degree hybrid. I also had the opportunity to study Alan
Podell's amazing designs and even have discussions with him.
I dissected one of his 10-3000 MHz hybrids. (Originally made
by Anzac, now available from Macom Technology for about 5 Benjamins).
Don't even think about trying this at home.
BTW, you didn't mention software, but that's a big part of
the job.
Rick Karlquist N6RK
On Mon, 2 Jun 2014 11:09:55 -0400
Scott McGrath scmcgrath@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
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
The design of an VNA is an interesting thing. It requires quite high focus
on good RF practices and screening.
In the range 0-3GHz there is no low cost devices avaible, not counting the
copper mountain tech boxes ( http://www.coppermountaintech.com/ ). Up to
1.3GHz there is the DG8SAQ VNWA avaible from sdrkits, these can also be
used with mixers to extend the max frequency. The VNWA is an 2 detector VNA
that needs an S-parameter testset in order to get all the 4 S-parameters.
An homebrew alternative would be fun to do, but its a lot of work, both in
getting reproduceable data from the hardware and in programming. Building
somthing that is connected to the PC simplifies things a lot.
Couplers and detectors are not the hardest thing to make, some small SMD
resistors, an balanced amplifier - detector and things should work to 6GHz
or higher with some care in the layout.
Signal generation is perhaps the hardest part, there is AFAIK no single
solution working from LF to high UHF, one cool alternative is to build an
generator with an YIG and mixing down, but that requires a lot of work to
get stable over the range 0-3GHz. In addition you need to keep the signal
from the generator out of the detector in order to keep the dynamic range
high.
If you are building your own VNA, I would build it with 4 detectors and the
posibility to re-configure those. It opens for several of the more advanced
calibration methods and eliminates some of the errors in the VNA.
If I were to build something, I think I would base it on the N2PK design,
as there is documentation and programs avaible that makes for some part of
the work.
There are some IC's avaible that do the detection of the power levels,
AD8302 comes to mind, the common denominator for these are that they don't
solve for the phase sign, and thereby are not true vector. In addition,
those I have tested don't behave to well with
As an alternative, the HP8410 series are avaible here in the EU, sometimes
quite cheap, if you can wait a bit. Mine is mostly used at microwaves, with
some external mixers and testsets. If you are low on cash, this may be the
best approach, but it requires some work.
The accuracy of the VNA is determined by the calkit used to calibrate it.
There is no way around obtaining an good calkit, learning how to use it
without destroying it, and do repeatable calibrations. The calkit is the
single most important part of the VNA. Do use an calkit for the connectors
you are going to measure, don't add adaptors or worse, coaxial cable after
the calibration plane.
The book by Joel Dunsmore is excelent, highly reccomended if you are doing
or interested in VNA measurments.
BR.
Thomas.
2014-06-02 16:43 GMT+02:00 Attila Kinali attila@kinali.ch:
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
--
The trouble with you, Shev, is you don't say anything until you've saved
up a whole truckload of damned heavy brick arguments and then you dump
them all out and never look at the bleeding body mangled beneath the heap
-- Tirin, The Dispossessed, U. Le Guin
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Please avoid sending me Word or PowerPoint attachments.
See http://www.gnu.org/philosophy/no-word-attachments.html
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On Mon, 2 Jun 2014 09:01:37 -0700
Chris Albertson albertson.chris@gmail.com wrote:
Today you can do most of the processing in software. All you need is A/D
and D/A converters that can handle the required bandwidth and get the raw
numbers into the computer. Look up "SDR" type radios and search on the
combination of SDR and VNA and you'll find a few. Then with the same
hardware you have a VNA, spectrum analyzer, oscilloscope, low power
transceiver and so on. This idea is somewhat easy through HF.
That's actually the base idea. Get some wide range synthesizer
(eg like HMC832LP6GE or LTC6946) for the test signal and one for
the detection part. Mix down the received signal and use some ADC
to move into digital domain. There preprocess the data in an FPGA
(data reduction) and do all difficult stuff in the PC.
Yes, it all sounds so easy. But i'm sure there must be some trap
in there, which i cannot see yet.
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl
On Mon, 02 Jun 2014 09:46:38 -0600
Ed Palmer ed_palmer@sasktel.net wrote:
There's a DIY project to build a spectrum analyzer at
http://scottyspectrumanalyzer.com . Since it's modular, one version of
the project is to add a couple of modules that change it into a network
analyzer.
That looks very interesting. Thanks for the link!
If you search ebay for directional couplers, I can almost guarantee that
you will find what you want at a reasonable price.
Yes. But if i ever build something, it should be reproducible for
others as well. Thus i don't want to rely on stuff from ebay which
can suddenly disapear.
Attila Kinali
--
I pity people who can't find laughter or at least some bit of amusement in
the little doings of the day. I believe I could find something ridiculous
even in the saddest moment, if necessary. It has nothing to do with being
superficial. It's a matter of joy in life.
-- Sophie Scholl