Re: [time-nuts] DIY VNA design

[Brooke Clarke]

Hi Dave:

I worked on the HP/Agilent 4380S test system software.  The 4380A test set has 8 ports and 3 receivers (R, A & B) as 
well as a built-in Short - Open - Load to speed up the calibration.  Uses bridges.

http://www.prc68.com/I/4395A.shtml#4380
Used for measuring both ends of CAT5 cable and Firewire where each wire gets a test port. S-parameters transformed into 
Z-parameters to balanced parameters.  Note this system can test BALUNS where one port is coax and the other balanced 
terminals.


--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.

 Original Message 



On 8/21/2016 3:59 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:


That said, I don't know why the author is using directional couplers.  A
bridge is much wider bandwidth.  It is more lossy though.


In general, a resistive bridge will always require a
transformer/180 degree hybrid/differential amplifier
to make it work.  If you are going to go to the trouble
of making a broadband transformer or hybrid, you might
as well just build a traditional directional coupler,
because it is no more difficult.  All the resistive
bridges I have seen are followed by broadband differential
amplifiers.  The resistive bridge itself has a minimum of
something like 15 to 20 dB loss, and the differential
amplifier has a minimum NF of 7 dB or so.  This results
in a great loss of sensitivity, but you can always get
the sensitivity back by using a narrow IF bandwidth and/or
lots of averaging, or (rarely) a high drive level from
the source.

Having said that, one of the putative advantages of a resistive
bridge is accuracy.  However, with today's calibration techniques,
this is no longer all that important, so a traditional coupler
might be more practical than it used to be.  I remember attending
the retirement party of Agilent's last great designer of couplers
(pre-calibration) and let me tell you, this guy was a total guru.
He was one of greatest practitioners in this area of all time.
He freely admitted that he was now obsolete due to calibration.
Any old coupler is good enough.





Anyway,  it is an interesting project, but personally if I were going to
go to the effort of building a 2-port VNA, I would build one with 4
receivers.

Dave
___


We used to have a lot of arguments at Agilent about how many
receivers were needed.  The most I ever heard advocated was 5,
and the least was 1 or 2.  I had to intervene in some of these
arguments to bring up what I call the "back door reference"
fallacy.  If you were making a "scalar" network analyzer that
only dealt with amplitude, you could make various arguments
about why you don't need so many receivers.  In principle,
1 receiver could work.  (The achilles heel of this idea
turns out to be imperfect repeatability of switches, and
very long settling times and thermal tails in switches.
None of these calibrate out).

In any event, as soon as you start talking about vector
network analyzers, you are measuring phase.  Unlike amplitude,
phase is always a relative measurement.  That is why you
need a reference ("R" channel).  You compute A/R.  This
requires a minimum of 2 receivers, an "A" and an "R".
Concurrently, not consecutively.  Architectures that skimp
on receiver count, or ostensibly omit the reference channel,
are really a cheat.  There will be some back channel between
the instrument clock and the sampling clock in the ADC that
in essence acts as a reference channel.  If there is any
warm up drift in the phase of this channel, you will get
non-correctable errors if you try to multiplex a single
receiver.  It is also another source of crosstalk on the
PC board.

Another problem with skimping on receivers is that you
can't do full 2 port calibration, I used to
have people show me "proof of concept" why they don't need
full 2 port calibration.  They would compare a test of
some simplified architecture to some top of the line VNA
and show that the measurements were the "same".  Just like
the graphs you see comparing low cost VNA's to Agilent
VNA's (it always seems to be Agilent, not one of the other
name brands).  It would often turn out that these "benchmarks"
were not good tests of the analyzer.  Changing to more
challenging tests would reveal the true superior design.

For example, if you calibrate with a short, open, and load,
and then measure the short, it always looks perfect.  But
if you add a short length of transmission line in front of
it, the simplified architecture may not work so well any
more.  This is called a "remote short" test.

Rick
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Re: [time-nuts] DIY VNA design [VNA-Nuts?]

[Attila Kinali]

On Mon, 22 Aug 2016 23:56:12 -0700
Hal Murray  wrote:

> att...@kinali.ch said:
> > Is there any advantage of using groups.io compared to a traditional
> > mailinglist? If not, I would prefer a traditional mailinglist. But maybe I
> > am just oldfashioned :-) 
> 
> The obvious advantage is that there is a professional staff keeping things 
> running so you don't need your own admin/wizard.

But be aware that professional does not mean they are proficient,
just they are paid for doing it. Back in the days, MPlayer and FFmpeg
were hosted on sourceforge. We had about one outage/something not working
correctly once per month.. at least. When we moved to our own infrastructure
all problems went away. In the 10 years I took care of it, there was a total
downtime of about 2 or 3 days. febo.com (John Ackermans site which hosts
time-nuts) shows a similar track record, probably even better. Show me one
commercial service that has the same up-time performance. 

Also, a couple of us already have the required infrastructure running.
Adding another mailinglist would not be a problem.
 
Anyways.. this is getting way too off topic, so I make this my last mail
on this.

If anyone wants, I can host the mailinglist. Or we can ask John.


Attila Kinali
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] DIY VNA design [VNA-Nuts?]

[Hal Murray]

att...@kinali.ch said:
> Is there any advantage of using groups.io compared to a traditional
> mailinglist? If not, I would prefer a traditional mailinglist. But maybe I
> am just oldfashioned :-) 

The obvious advantage is that there is a professional staff keeping things 
running so you don't need your own admin/wizard.

The part I'm missing is where do they get their cash?  Are they adding ads?  
(maybe only on the web version)  Are they collecting data and selling it?  
(This list is public so a lot of data is already available.)

-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] DIY VNA design [VNA-Nuts?]

[David]

On Mon, 22 Aug 2016 23:44:17 +0200, you wrote:

>On Mon, 22 Aug 2016 14:20:59 -0400
>Bob Bownes  wrote:
>
>> Just finished creating it at groups.io
>>
>> *https://groups.io/g/svna *
>> and sign up. :)
>
>Is there any advantage of using groups.io compared to a traditional
>mailinglist? If not, I would prefer a traditional mailinglist.
>But maybe I am just oldfashioned :-)
>
>   Attila Kinali

It has features not typically associated with mailing lists like web
access (yuck!) and file storage and if abandoning a Yahoo group, they
can transfer the old contents over.  Traditional email clients can
still be used for access and I think threading works although I have
not really tested it.
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Re: [time-nuts] DIY VNA design

[jimlux]

On 8/22/16 5:01 PM, Richard (Rick) Karlquist wrote:



On 8/21/2016 3:59 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:


That said, I don't know why the author is using directional couplers.  A
bridge is much wider bandwidth.  It is more lossy though.


In general, a resistive bridge will always require a
transformer/180 degree hybrid/differential amplifier
to make it work.  If you are going to go to the trouble
of making a broadband transformer or hybrid, you might
as well just build a traditional directional coupler,
because it is no more difficult.  All the resistive
bridges I have seen are followed by broadband differential
amplifiers.  The resistive bridge itself has a minimum of
something like 15 to 20 dB loss, and the differential
amplifier has a minimum NF of 7 dB or so.  This results
in a great loss of sensitivity, but you can always get
the sensitivity back by using a narrow IF bandwidth and/or
lots of averaging, or (rarely) a high drive level from
the source.

Having said that, one of the putative advantages of a resistive
bridge is accuracy.  However, with today's calibration techniques,
this is no longer all that important, so a traditional coupler
might be more practical than it used to be.  I remember attending
the retirement party of Agilent's last great designer of couplers
(pre-calibration) and let me tell you, this guy was a total guru.
He was one of greatest practitioners in this area of all time.
He freely admitted that he was now obsolete due to calibration.
Any old coupler is good enough.






these days, what you want is repeatability, so that you can "calibrate" 
and have the calibration remain stable.



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Re: [time-nuts] DIY VNA design

[Jim Cotton]

The intersection of HP equipment && Time-Nuts && VNWA mailing lists is >>

At least two ;^)

Jim 
n8qoh


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Re: [time-nuts] DIY VNA design

[Richard (Rick) Karlquist]

On 8/21/2016 3:59 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:


That said, I don't know why the author is using directional couplers.  A
bridge is much wider bandwidth.  It is more lossy though.


In general, a resistive bridge will always require a
transformer/180 degree hybrid/differential amplifier
to make it work.  If you are going to go to the trouble
of making a broadband transformer or hybrid, you might
as well just build a traditional directional coupler,
because it is no more difficult.  All the resistive
bridges I have seen are followed by broadband differential
amplifiers.  The resistive bridge itself has a minimum of
something like 15 to 20 dB loss, and the differential
amplifier has a minimum NF of 7 dB or so.  This results
in a great loss of sensitivity, but you can always get
the sensitivity back by using a narrow IF bandwidth and/or
lots of averaging, or (rarely) a high drive level from
the source.

Having said that, one of the putative advantages of a resistive
bridge is accuracy.  However, with today's calibration techniques,
this is no longer all that important, so a traditional coupler
might be more practical than it used to be.  I remember attending
the retirement party of Agilent's last great designer of couplers
(pre-calibration) and let me tell you, this guy was a total guru.
He was one of greatest practitioners in this area of all time.
He freely admitted that he was now obsolete due to calibration.
Any old coupler is good enough.





Anyway,  it is an interesting project,  but personally if I were going to
go to the effort of building a 2-port VNA, I would build one with 4
receivers.

Dave
___


We used to have a lot of arguments at Agilent about how many
receivers were needed.  The most I ever heard advocated was 5,
and the least was 1 or 2.  I had to intervene in some of these
arguments to bring up what I call the "back door reference"
fallacy.  If you were making a "scalar" network analyzer that
only dealt with amplitude, you could make various arguments
about why you don't need so many receivers.  In principle,
1 receiver could work.  (The achilles heel of this idea
turns out to be imperfect repeatability of switches, and
very long settling times and thermal tails in switches.
None of these calibrate out).

In any event, as soon as you start talking about vector
network analyzers, you are measuring phase.  Unlike amplitude,
phase is always a relative measurement.  That is why you
need a reference ("R" channel).  You compute A/R.  This
requires a minimum of 2 receivers, an "A" and an "R".
Concurrently, not consecutively.  Architectures that skimp
on receiver count, or ostensibly omit the reference channel,
are really a cheat.  There will be some back channel between
the instrument clock and the sampling clock in the ADC that
in essence acts as a reference channel.  If there is any
warm up drift in the phase of this channel, you will get
non-correctable errors if you try to multiplex a single
receiver.  It is also another source of crosstalk on the
PC board.

Another problem with skimping on receivers is that you
can't do full 2 port calibration, I used to
have people show me "proof of concept" why they don't need
full 2 port calibration.  They would compare a test of
some simplified architecture to some top of the line VNA
and show that the measurements were the "same".  Just like
the graphs you see comparing low cost VNA's to Agilent
VNA's (it always seems to be Agilent, not one of the other
name brands).  It would often turn out that these "benchmarks"
were not good tests of the analyzer.  Changing to more
challenging tests would reveal the true superior design.

For example, if you calibrate with a short, open, and load,
and then measure the short, it always looks perfect.  But
if you add a short length of transmission line in front of
it, the simplified architecture may not work so well any
more.  This is called a "remote short" test.

Rick
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Re: [time-nuts] DIY VNA design [VNA-Nuts?]

[David & Laura]

I also prefer old-style e-mail-only mailing lists. Fortunately, you can
subscribe to a groups.io mailing list via e-mail. Just send “SUBSCRIBE" in
the body to svna+subscr...@groups.io

Thanks,

David Slik
VE7FIM

On Mon, Aug 22, 2016 at 3:08 PM, Wes  wrote:

> I agree.
>
> On 8/22/2016 2:44 PM, Attila Kinali wrote:
>
>> On Mon, 22 Aug 2016 14:20:59 -0400
>> Bob Bownes  wrote:
>>
>> Just finished creating it at groups.io
>>>
>>> *https://groups.io/g/svna *
>>> and sign up. :)
>>>
>> Is there any advantage of using groups.io compared to a traditional
>> mailinglist? If not, I would prefer a traditional mailinglist.
>> But maybe I am just oldfashioned :-)
>>
>> Attila Kinali
>>
>>
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/m
> ailman/listinfo/time-nuts
> and follow the instructions there.
>
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Re: [time-nuts] DIY VNA design [VNA-Nuts?]

[Wes]

I agree.

On 8/22/2016 2:44 PM, Attila Kinali wrote:

On Mon, 22 Aug 2016 14:20:59 -0400
Bob Bownes  wrote:


Just finished creating it at groups.io

*https://groups.io/g/svna *
and sign up. :)

Is there any advantage of using groups.io compared to a traditional
mailinglist? If not, I would prefer a traditional mailinglist.
But maybe I am just oldfashioned :-)

Attila Kinali



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Re: [time-nuts] DIY VNA design [VNA-Nuts?]

[Attila Kinali]

On Mon, 22 Aug 2016 14:20:59 -0400
Bob Bownes  wrote:

> Just finished creating it at groups.io
>
> *https://groups.io/g/svna *
> and sign up. :)

Is there any advantage of using groups.io compared to a traditional
mailinglist? If not, I would prefer a traditional mailinglist.
But maybe I am just oldfashioned :-)

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] DIY VNA design [VNA-Nuts?]

[Bob Bownes]

Just finished creating it at groups.io



*https://groups.io/g/svna <https://groups.io/g/svna>*
and sign up. :)


On Mon, Aug 22, 2016 at 12:38 PM, Tom Miller <tmiller11...@verizon.net>
wrote:

> Maybe do it on Mewe.com?
>
> - Original Message - From: "Oz-in-DFW" <li...@ozindfw.net>
> To: <time-nuts@febo.com>
> Sent: Monday, August 22, 2016 11:53 AM
> Subject: Re: [time-nuts] DIY VNA design [VNA-Nuts?]
>
>
>
> So is it time for VNA-Nuts?  I can probably host it.
>>
>> --
>> mailto:o...@ozindfw.net
>> Oz
>> POB 93167
>> Southlake, TX 76092 (Near DFW Airport)
>>
>>
>>
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/m
>> ailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
> ___
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> To unsubscribe, go to https://www.febo.com/cgi-bin/m
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>
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Re: [time-nuts] DIY VNA design [VNA-Nuts?]

[Tom Miller]

Maybe do it on Mewe.com?

- Original Message - 
From: "Oz-in-DFW" <li...@ozindfw.net>

To: <time-nuts@febo.com>
Sent: Monday, August 22, 2016 11:53 AM
Subject: Re: [time-nuts] DIY VNA design [VNA-Nuts?]



So is it time for VNA-Nuts?  I can probably host it.

--
mailto:o...@ozindfw.net
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)



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Re: [time-nuts] DIY VNA design [VNA-Nuts?]

[Oz-in-DFW]

So is it time for VNA-Nuts?  I can probably host it.

-- 
mailto:o...@ozindfw.net
Oz
POB 93167 
Southlake, TX 76092 (Near DFW Airport) 



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Re: [time-nuts] DIY VNA design, directional coupler

[Charles Steinmetz]

Alexander wrote:


there is a current mode feedback device [which does not follows the gain
bandwidth product role ] and has 1000V/usec rise time 92dB THD at 30MHz
3nV/rtHz noise


Yeah, but look at its 1/f input voltage noise corner -- it's at 2 or 3 
MHz!!!  So the baseband input noise density is over 1000nV/sqrtHz at 
1Hz, with potentially devastating effects on the phase noise performance 
in phase measurement applications.  (See Figures 18 and 56 of the cited 
datasheet.)


Even if the internal amplifier topology exhibits relatively low AM-PM 
conversion, starting that far behind is not a promising way to design a 
low-PN widget.


NFL

Best regards,

Charles


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Re: [time-nuts] DIY VNA design

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 22 August 2016 at 02:51, bownes  wrote:

>
> Comment inline
>
>
> > On Aug 21, 2016, at 18:59, Dr. David Kirkby (Kirkby Microwave Ltd) <
> drkir...@kirkbymicrowave.co.uk> wrote:
> >
> > I am not convinced that this is time-nuts related,  although I am sure
> many
> > time-nuts either have a VNA or would like one. Such a project needs its
> own
> > forum.
> >
>
> v...@yahoogroups.com would be the place.
>

I doubt it would be, although one should ask Tom Baier. I don't suppose he
would mind some discussion, but the topic of VNA design is so large and
complex that it could generate a huge volume of messages, which are way
outside the scope of the VNWA group.

I do know of another possible reason he might be a bit reluctant too. I
made a post on there once about the fact I had measured the N connector on
a brand new competitive product (RigExpert AA-600) and found it was out of
spec - photos at

http://www.dhars.org.uk/RigExpert-AA-600/

That resulted in the manufacturer of the RigExpert contacting Tom, as they
were unhappy about my comments. (Strangely they never contacted me!) I
received a phone call from Jan, the UK distributor about it. Basically they
did not want to get into a war with other companies like RigExpert. I can
see that discussions about VNAs in general could lead to discussions
comparing products.

In some ways it would be good if there was a forum for VNAs, and similar
instruments, which is not tied to any particular manufacturer. I'm not
aware of any. There's the HP/Yahoo list, VNWA and there's the Keysight
forums. Those are all specific to one manufacturer.

There are a number of techniques for measuring impedance, and the VNA is
just one of them. Keysight have no forums for LCR meters or impedance
analyzers, despite they sell the things.


>
> The intersection of HP equipment && Time-Nuts && VNWA mailing lists is >>
> 1 :)
>
>
Yes, very true. I'm certainly one of them, but as you say, it would be >>
1.

Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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Re: [time-nuts] DIY VNA design

[Bob kb8tq]

Hi

If you really want to work out the delays through all of this
GPS "stuff" ahead of the RF -> PPS conversion, a VNA is about
the only good way to do it. 

Bob

> On Aug 21, 2016, at 6:59 PM, Dr. David Kirkby (Kirkby Microwave Ltd) 
>  wrote:
> 
>> On 21 Aug 2016 03:19, "Attila Kinali"  wrote:
>> 
>> Moin,
>> 
>> I stumbled over a new open hardware/source VNA design:
> http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html
>> 
>> Unlike other designs out there, this one is very well done and has very
>> little room for improvement, without increasing the price considerably.
> 
> I am not convinced that this is time-nuts related,  although I am sure many
> time-nuts either have a VNA or would like one. Such a project needs its own
> forum.
> 
> That said, I don't know why the author is using directional couplers.  A
> bridge is much wider bandwidth.  It is more lossy though.
> 
> The software is I believe the tricky part. The VNWA software is very
> sophisticated, with a lot of useful features like it can design matching
> networks,   The software in the PNA-X is very sophisticated too, but in
> different ways.
> 
> I don't know what the author uses, but Qt seems like best choice to me,
> which can be be built on OSX, Linux and Windows.
> 
> For many measurements power levelling is not required, so that bit could be
> dispensed with.
> 
> The author seems of the opinion that a lot of the hardware imperfections
> can be corrected in software. Thak is true, but the the residual errors
> that remain are a function of the quality of the hardware.
> 
> Anyway,  it is an interesting project,  but personally if I were going to
> go to the effort of building a 2-port VNA, I would build one with 4
> receivers.
> 
> Dave
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Re: [time-nuts] DIY VNA design

[bownes]

Comment inline


> On Aug 21, 2016, at 18:59, Dr. David Kirkby (Kirkby Microwave Ltd) 
>  wrote:
> 
> I am not convinced that this is time-nuts related,  although I am sure many
> time-nuts either have a VNA or would like one. Such a project needs its own
> forum.
> 

v...@yahoogroups.com would be the place. 

The intersection of HP equipment && Time-Nuts && VNWA mailing lists is >> 1 :)

> 
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Re: [time-nuts] DIY VNA design

[Bob kb8tq]

Hi

One option in the "1 GHz and down" range is to team up a surplus HP S-Parameter 
test set with your own electronics. That way you let HP do all of the fancy 
directional coupler stuff and relays. They don't sell well on the auction 
sites. The result is that a bit of time making lowball offers can generally get 
you one or more of them for not a whole lot of money. 

Bob

> On Aug 21, 2016, at 12:46 AM, Bob Albert via time-nuts  
> wrote:
> 
> I was interested in this, but my needs are mostly below 100 MHz.  I wonder 
> what could be done similarly for this lower range...
> Bob
> 
> 
>On Saturday, August 20, 2016 8:54 PM, Richard (Rick) Karlquist 
>  wrote:
> 
> 
> Another great posting, Attila.
> 
> When I was with Agilent, we looked at all kinds of
> simplified network analyzer architectures, and I
> would have to say the author is really well informed.
> One issue he doesn't seem to be aware of is that the
> ADL5801, when driven single ended, has some quirks
> below 100 MHz that I discovered experimentally.
> (The data sheet is silent on this).  IMHO, it
> would be worth 7 Euro's to use a balun, however,
> I would like to know the part number of this
> supposed component.  I am not so sure about MCL
> actually covering 30 MHz to 6 GHz in the same
> balun.  Sometimes their advertising is confusing,
> and when they say .03-6 GHz baluns, they mean
> that the range can be covered in several bands
> by several model numbers.
> 
> Still, quite impressive work by an individual
> practitioner.
> 
> Rick
> 
>> On 8/20/2016 7:19 PM, Attila Kinali wrote:
>> Moin,
>> 
>> I stumbled over a new open hardware/source VNA design:
>> http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html
>> 
>> Unlike other designs out there, this one is very well done and has very
>> little room for improvement, without increasing the price considerably.
>> 
>> About the only things i would do different is to use two receiver
>> channels, one fix connected at the TX source to be able to do a
>> difference measurement between TX and the RX channels and thus
>> improving precision. And the other would be to use a dual ADC
>> with an FPGA for the data processing, again in order to increase
>> performance.
>> 
>> But as I wrote, both changes would increase complexity and price.
>> 
>> Other than being a well thought through design, the website also
>> explains all the big design choices and why this or that has been
>> done instead of one of the many alternatives. That alone makes it
>> worth reading, IMHO.
>> 
>> Attila Kinali
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> 
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Re: [time-nuts] DIY VNA design

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 21 Aug 2016 03:19, "Attila Kinali"  wrote:
>
> Moin,
>
> I stumbled over a new open hardware/source VNA design:
>
http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html
>
> Unlike other designs out there, this one is very well done and has very
> little room for improvement, without increasing the price considerably.

I am not convinced that this is time-nuts related,  although I am sure many
time-nuts either have a VNA or would like one. Such a project needs its own
forum.

That said, I don't know why the author is using directional couplers.  A
bridge is much wider bandwidth.  It is more lossy though.

The software is I believe the tricky part. The VNWA software is very
sophisticated, with a lot of useful features like it can design matching
networks,   The software in the PNA-X is very sophisticated too, but in
different ways.

I don't know what the author uses, but Qt seems like best choice to me,
which can be be built on OSX, Linux and Windows.

For many measurements power levelling is not required, so that bit could be
dispensed with.

The author seems of the opinion that a lot of the hardware imperfections
can be corrected in software. Thak is true, but the the residual errors
that remain are a function of the quality of the hardware.

Anyway,  it is an interesting project,  but personally if I were going to
go to the effort of building a 2-port VNA, I would build one with 4
receivers.

Dave
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Re: [time-nuts] DIY VNA design, directional coupler

[Alexander Pummer]

there is a current mode feedback device [which does not follows the gain 
bandwidth product role ] and has 1000V/usec rise time 92dB THD at 30MHz  
3nV/rtHz noise, see here http://www.ti.com/lit/ds/symlink/ths4271.pdf, I 
used it as a medical color Doppler application


Guanella's choke and Guanellas balun are two different animals, the 
balun has a cross DC path, the choke does not have, it's other name is 
1:1 transmission line transformer,  in conjunction with an A/D converter 
the choke has the function to prevent a current path to the ground via 
one of the the differential inputs, also used in high dynamic range 
medical ultrasound application


73

Alex


On 8/21/2016 1:29 PM, Attila Kinali wrote:

On Sun, 21 Aug 2016 10:04:10 -0700
Alex Pummer  wrote:


directional coupler/circulator could be made with high bandwidth [ up to
1GHz ] operational amplifiers, that circulator will work from DC..

While this is a valid option, it would then become the element in the
system that limits dynamic range. It's better to use a "noiseless"
passive circuit that has very little distortion.

Also keep in mind that even if the opamp has an GBW of 1GHz or more,
the slewrate kicks in quite early and in this case would limit the
maximum signal strength severely. There is a reason why GHz amplifiers
use so much power.


driving A/D converter input asymmetrically; drive trough a
Guanella-choke, but match the output of the choke

The Guanella balun, like all other transformer based baluns,
has the same upper and lower frequency limits: The inductance
sets the lower limit (more inductance -> lower frequency) and
the loss in the ferrite sets the upper limit (non-linear and thus
can be quite abrupt). Another issue here is symmetry of output
over frequency (c.f. [1]). I don't know how good the Guanella
baluns are in reality, but this is definitly something that should
be looked at.


Attila Kinali

[1] 
http://www.markimicrowave.com/blog/2013/07/why-buy-a-high-quality-baluntransformer-for-an-analog-to-digital-converter-adc/


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Re: [time-nuts] DIY VNA design, directional coupler

[Attila Kinali]

On Sun, 21 Aug 2016 10:04:10 -0700
Alex Pummer  wrote:

> directional coupler/circulator could be made with high bandwidth [ up to 
> 1GHz ] operational amplifiers, that circulator will work from DC..

While this is a valid option, it would then become the element in the
system that limits dynamic range. It's better to use a "noiseless"
passive circuit that has very little distortion.

Also keep in mind that even if the opamp has an GBW of 1GHz or more,
the slewrate kicks in quite early and in this case would limit the
maximum signal strength severely. There is a reason why GHz amplifiers
use so much power.

> driving A/D converter input asymmetrically; drive trough a 
> Guanella-choke, but match the output of the choke

The Guanella balun, like all other transformer based baluns,
has the same upper and lower frequency limits: The inductance
sets the lower limit (more inductance -> lower frequency) and
the loss in the ferrite sets the upper limit (non-linear and thus
can be quite abrupt). Another issue here is symmetry of output
over frequency (c.f. [1]). I don't know how good the Guanella
baluns are in reality, but this is definitly something that should
be looked at.


Attila Kinali

[1] 
http://www.markimicrowave.com/blog/2013/07/why-buy-a-high-quality-baluntransformer-for-an-analog-to-digital-converter-adc/
-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] DIY VNA design

[Wes]

I built an original N2PK, that interfaced via a parallel port.  I did a minor 
upgrade that changed to an improved DAC.  I still have a Win XP laptop with a 
parallel port so can still use it.  Later it was refined to USB but I never 
upgraded, although I still have the unpopulated circuit boards for the later 
configuration.


The reason for not finishing the project, other than time, is the fact that I 
bought the other ANA under discussion, the VNWA-3.


As someone who started using a grease pencil on the CRT for "calibration" of a 
waveguide reflectometer, graduated to an HP8410 then an HP8510, I never cease to 
be amazed that I can hold something with similar accuracy (albeit less frequency 
range) in the palm of my hand.


Wes

On 8/20/2016 11:37 PM, Bob Albert via time-nuts wrote:

Well that's a start.  Thanks for the link!  I would need more information, as 
this project goes into areas that are new to me.  And there is no clue as to 
the cost of construction.
But I'll study what's there and if nothing else, learn something.
Bob
  


 On Saturday, August 20, 2016 10:46 PM, Orin Eman  
wrote:
  


  To 60MHz: http://n2pk.com; PCBs available here: http://www.makarov.ca/vna.htm
To 500MHz, lower dynamic range to 1.3GHz: 
http://sdr-kits.net/VNWA3_Description.html
OK, so the latter isn't build it yourself anymore.
I have version 2.6 of the latter and it works really well to about 575MHz.  
Traces can get noisy after about 575MHz.
Remember these VNAs are only as good as the calibration kit you use with them!
Orin.

On Sat, Aug 20, 2016 at 9:46 PM, Bob Albert via time-nuts  
wrote:

I was interested in this, but my needs are mostly below 100 MHz.  I wonder what 
could be done similarly for this lower range...
Bob


 On Saturday, August 20, 2016 8:54 PM, Richard (Rick) Karlquist 
 wrote:


  Another great posting, Attila.

When I was with Agilent, we looked at all kinds of
simplified network analyzer architectures, and I
would have to say the author is really well informed.
One issue he doesn't seem to be aware of is that the
ADL5801, when driven single ended, has some quirks
below 100 MHz that I discovered experimentally.
(The data sheet is silent on this).  IMHO, it
would be worth 7 Euro's to use a balun, however,
I would like to know the part number of this
supposed component.  I am not so sure about MCL
actually covering 30 MHz to 6 GHz in the same
balun.  Sometimes their advertising is confusing,
and when they say .03-6 GHz baluns, they mean
that the range can be covered in several bands
by several model numbers.

Still, quite impressive work by an individual
practitioner.

Rick

On 8/20/2016 7:19 PM, Attila Kinali wrote:

Moin,

I stumbled over a new open hardware/source VNA design:
http://hforsten.com/cheap- homemade-30-mhz-6-ghz-vector- network-analyzer.html

Unlike other designs out there, this one is very well done and has very
little room for improvement, without increasing the price considerably.

About the only things i would do different is to use two receiver
channels, one fix connected at the TX source to be able to do a
difference measurement between TX and the RX channels and thus
improving precision. And the other would be to use a dual ADC
with an FPGA for the data processing, again in order to increase
performance.

But as I wrote, both changes would increase complexity and price.

Other than being a well thought through design, the website also
explains all the big design choices and why this or that has been
done instead of one of the many alternatives. That alone makes it
worth reading, IMHO.

 Attila Kinali




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Re: [time-nuts] DIY VNA design, directional coupler

[Alex Pummer]

directional coupler/circulator could be made with high bandwidth [ up to 
1GHz ] operational amplifiers, that circulator will work from DC..


driving A/D converter input asymmetrically; drive trough a 
Guanella-choke, but match the output of the choke


73

Alex


On 8/21/2016 3:21 AM, Attila Kinali wrote:

On Sun, 21 Aug 2016 04:46:10 + (UTC)
Bob Albert via time-nuts  wrote:


I was interested in this, but my needs are mostly below 100 MHz.
I wonder what could be done similarly for this lower range...

As Orin mentioned, there are some designs for that range out there,
best known are probably the two Orin listed (N2PK and the VNAW by DG8SAQ).
Although these are good designs, they are not as good as the one by
Henrik Forstén. Henrik addresses many issues that the other leave out
for simplicity.

What I would do instead is use Henrik's design and do some adaptions.
There are four parts that limit the frequency at the lower end:
the signal sources, the filters for the sources, the mixer and
the directional couplers.

For the signal source there are two choices: DDS and down-mixing.
The DDS is probably the obvious choice and delivers good results,
but limits the maximum frequency if you have price limit.
The down-mixing approach uses one of the PLL's with VCO as the
original design uses, but only within a limited range, eg around
200MHz. This signal can then be down-mixed using a crystal oscillator
(or another PLL+VCO) and a suitable mixer (eg LTC5512 or a DIY diode mixer).
Advantage of this is, that the spurs of the PLL+VCO can be surpressed
to a large extend, as the frequency range is quite narrow relative to
the output frequency of the PLL+VCO.

For the directional couplers, the approach used with Henriks design
will not work for low frequencies, as this type of coupler needs a length
of approximately lambda/4 to work optimally. I.e. they would become
unweildingly large. The two choices I am aware of for the lower frequency
ranges are transformer based directional couplers or resistive bridges.
Transformer based couplers have the disadvantage of a non-flat frequency
response and an upper and lower frequency limit, given by the characteristics
of the transformer (number of windings/inductance and the used ferrite).
Their advantage is that they have very little loss. Resistive bridges on
the other hand have a loss of 3db (respectively a -6dB signal at each output),
but are totally flat down to DC and up to several hundred MHz or even GHz if
RF resistors are used.


Most of the above mentioned methods have a lower frequency limit somewhere in
the range of 20kHz and ~100kHz. If you want to go below that limit, you will
need to adapt the circuit further:
For the signal source the DDS approach is the only one that will result
in a good SNR at a reasonable price. Easiest way to go is to use a 16bit
DAC at >1MHz and an uC or FPGA to feed it (but use some low jitter oscillator
as clock source for the DAC). The other components in the signal path
that are limiting are the baluns and mixers. I would get rid of those two
all-together and digitize the signal from the directional couplers directly
using an ADC with >1Msps and 16-18bit. If you limit yourself to the range
of 10Hz-20kHz, you can do all this using audio ADC/DACs and get a very
high performing system.

Attila Kinali



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Re: [time-nuts] DIY VNA design

[Attila Kinali]

On Sun, 21 Aug 2016 04:46:10 + (UTC)
Bob Albert via time-nuts  wrote:

> I was interested in this, but my needs are mostly below 100 MHz.
> I wonder what could be done similarly for this lower range...

As Orin mentioned, there are some designs for that range out there,
best known are probably the two Orin listed (N2PK and the VNAW by DG8SAQ).
Although these are good designs, they are not as good as the one by
Henrik Forstén. Henrik addresses many issues that the other leave out
for simplicity. 

What I would do instead is use Henrik's design and do some adaptions.
There are four parts that limit the frequency at the lower end:
the signal sources, the filters for the sources, the mixer and
the directional couplers.

For the signal source there are two choices: DDS and down-mixing.
The DDS is probably the obvious choice and delivers good results,
but limits the maximum frequency if you have price limit. 
The down-mixing approach uses one of the PLL's with VCO as the
original design uses, but only within a limited range, eg around
200MHz. This signal can then be down-mixed using a crystal oscillator
(or another PLL+VCO) and a suitable mixer (eg LTC5512 or a DIY diode mixer).
Advantage of this is, that the spurs of the PLL+VCO can be surpressed
to a large extend, as the frequency range is quite narrow relative to
the output frequency of the PLL+VCO.

For the directional couplers, the approach used with Henriks design
will not work for low frequencies, as this type of coupler needs a length
of approximately lambda/4 to work optimally. I.e. they would become
unweildingly large. The two choices I am aware of for the lower frequency
ranges are transformer based directional couplers or resistive bridges.
Transformer based couplers have the disadvantage of a non-flat frequency
response and an upper and lower frequency limit, given by the characteristics
of the transformer (number of windings/inductance and the used ferrite). 
Their advantage is that they have very little loss. Resistive bridges on
the other hand have a loss of 3db (respectively a -6dB signal at each output),
but are totally flat down to DC and up to several hundred MHz or even GHz if
RF resistors are used.


Most of the above mentioned methods have a lower frequency limit somewhere in
the range of 20kHz and ~100kHz. If you want to go below that limit, you will
need to adapt the circuit further:
For the signal source the DDS approach is the only one that will result
in a good SNR at a reasonable price. Easiest way to go is to use a 16bit
DAC at >1MHz and an uC or FPGA to feed it (but use some low jitter oscillator
as clock source for the DAC). The other components in the signal path
that are limiting are the baluns and mixers. I would get rid of those two
all-together and digitize the signal from the directional couplers directly
using an ADC with >1Msps and 16-18bit. If you limit yourself to the range
of 10Hz-20kHz, you can do all this using audio ADC/DACs and get a very
high performing system.

Attila Kinali

-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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Re: [time-nuts] DIY VNA design

[David J Taylor]

[]
To 500MHz, lower dynamic range to 1.3GHz:
http://sdr-kits.net/VNWA3_Description.html

OK, so the latter isn't build it yourself anymore.

I have version 2.6 of the latter and it works really well to about 575MHz.
Traces can get noisy after about 575MHz.

Remember these VNAs are only as good as the calibration kit you use with
them!

Orin.
==

Folks,

I have one of these and it works really well, even up to 1.3 GHz.  I know 
that some have used it for characterising 32 kHz crystals so it works down 
at LF as well.


I can strongly recommend the support group as the source of much expertise, 
and it's regularly visited by the designer as well:


 http://groups.yahoo.com/group/VNWA/

Some of my own very simple plots:

 http://www.satsignal.eu/Radio/ddamtek-filters.html
 http://www.satsignal.eu/Radio/RX-filters.html#response

73,
David GM8ARV
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


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Re: [time-nuts] DIY VNA design

[Bob Albert via time-nuts]

Well that's a start.  Thanks for the link!  I would need more information, as 
this project goes into areas that are new to me.  And there is no clue as to 
the cost of construction.
But I'll study what's there and if nothing else, learn something.
Bob
 

On Saturday, August 20, 2016 10:46 PM, Orin Eman  
wrote:
 

 To 60MHz: http://n2pk.com; PCBs available here: http://www.makarov.ca/vna.htm
To 500MHz, lower dynamic range to 1.3GHz: 
http://sdr-kits.net/VNWA3_Description.html
OK, so the latter isn't build it yourself anymore.
I have version 2.6 of the latter and it works really well to about 575MHz.  
Traces can get noisy after about 575MHz.  
Remember these VNAs are only as good as the calibration kit you use with them!
Orin.

On Sat, Aug 20, 2016 at 9:46 PM, Bob Albert via time-nuts  
wrote:

I was interested in this, but my needs are mostly below 100 MHz.  I wonder what 
could be done similarly for this lower range...
Bob


    On Saturday, August 20, 2016 8:54 PM, Richard (Rick) Karlquist 
 wrote:


 Another great posting, Attila.

When I was with Agilent, we looked at all kinds of
simplified network analyzer architectures, and I
would have to say the author is really well informed.
One issue he doesn't seem to be aware of is that the
ADL5801, when driven single ended, has some quirks
below 100 MHz that I discovered experimentally.
(The data sheet is silent on this).  IMHO, it
would be worth 7 Euro's to use a balun, however,
I would like to know the part number of this
supposed component.  I am not so sure about MCL
actually covering 30 MHz to 6 GHz in the same
balun.  Sometimes their advertising is confusing,
and when they say .03-6 GHz baluns, they mean
that the range can be covered in several bands
by several model numbers.

Still, quite impressive work by an individual
practitioner.

Rick

On 8/20/2016 7:19 PM, Attila Kinali wrote:
> Moin,
>
> I stumbled over a new open hardware/source VNA design:
> http://hforsten.com/cheap- homemade-30-mhz-6-ghz-vector- network-analyzer.html
>
> Unlike other designs out there, this one is very well done and has very
> little room for improvement, without increasing the price considerably.
>
> About the only things i would do different is to use two receiver
> channels, one fix connected at the TX source to be able to do a
> difference measurement between TX and the RX channels and thus
> improving precision. And the other would be to use a dual ADC
> with an FPGA for the data processing, again in order to increase
> performance.
>
> But as I wrote, both changes would increase complexity and price.
>
> Other than being a well thought through design, the website also
> explains all the big design choices and why this or that has been
> done instead of one of the many alternatives. That alone makes it
> worth reading, IMHO.
>
>             Attila Kinali
>
>
>
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Re: [time-nuts] DIY VNA design

[Orin Eman]

To 60MHz: http://n2pk.com; PCBs available here:
http://www.makarov.ca/vna.htm

To 500MHz, lower dynamic range to 1.3GHz:
http://sdr-kits.net/VNWA3_Description.html

OK, so the latter isn't build it yourself anymore.

I have version 2.6 of the latter and it works really well to about 575MHz.
Traces can get noisy after about 575MHz.

Remember these VNAs are only as good as the calibration kit you use with
them!

Orin.


On Sat, Aug 20, 2016 at 9:46 PM, Bob Albert via time-nuts <
time-nuts@febo.com> wrote:

> I was interested in this, but my needs are mostly below 100 MHz.  I wonder
> what could be done similarly for this lower range...
> Bob
>
>
> On Saturday, August 20, 2016 8:54 PM, Richard (Rick) Karlquist <
> rich...@karlquist.com> wrote:
>
>
>  Another great posting, Attila.
>
> When I was with Agilent, we looked at all kinds of
> simplified network analyzer architectures, and I
> would have to say the author is really well informed.
> One issue he doesn't seem to be aware of is that the
> ADL5801, when driven single ended, has some quirks
> below 100 MHz that I discovered experimentally.
> (The data sheet is silent on this).  IMHO, it
> would be worth 7 Euro's to use a balun, however,
> I would like to know the part number of this
> supposed component.  I am not so sure about MCL
> actually covering 30 MHz to 6 GHz in the same
> balun.  Sometimes their advertising is confusing,
> and when they say .03-6 GHz baluns, they mean
> that the range can be covered in several bands
> by several model numbers.
>
> Still, quite impressive work by an individual
> practitioner.
>
> Rick
>
> On 8/20/2016 7:19 PM, Attila Kinali wrote:
> > Moin,
> >
> > I stumbled over a new open hardware/source VNA design:
> > http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-
> network-analyzer.html
> >
> > Unlike other designs out there, this one is very well done and has very
> > little room for improvement, without increasing the price considerably.
> >
> > About the only things i would do different is to use two receiver
> > channels, one fix connected at the TX source to be able to do a
> > difference measurement between TX and the RX channels and thus
> > improving precision. And the other would be to use a dual ADC
> > with an FPGA for the data processing, again in order to increase
> > performance.
> >
> > But as I wrote, both changes would increase complexity and price.
> >
> > Other than being a well thought through design, the website also
> > explains all the big design choices and why this or that has been
> > done instead of one of the many alternatives. That alone makes it
> > worth reading, IMHO.
> >
> > Attila Kinali
> >
> >
> >
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>
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Re: [time-nuts] DIY VNA design

[Bob Albert via time-nuts]

I was interested in this, but my needs are mostly below 100 MHz.  I wonder what 
could be done similarly for this lower range...
Bob
 

On Saturday, August 20, 2016 8:54 PM, Richard (Rick) Karlquist 
 wrote:
 

 Another great posting, Attila.

When I was with Agilent, we looked at all kinds of
simplified network analyzer architectures, and I
would have to say the author is really well informed.
One issue he doesn't seem to be aware of is that the
ADL5801, when driven single ended, has some quirks
below 100 MHz that I discovered experimentally.
(The data sheet is silent on this).  IMHO, it
would be worth 7 Euro's to use a balun, however,
I would like to know the part number of this
supposed component.  I am not so sure about MCL
actually covering 30 MHz to 6 GHz in the same
balun.  Sometimes their advertising is confusing,
and when they say .03-6 GHz baluns, they mean
that the range can be covered in several bands
by several model numbers.

Still, quite impressive work by an individual
practitioner.

Rick

On 8/20/2016 7:19 PM, Attila Kinali wrote:
> Moin,
>
> I stumbled over a new open hardware/source VNA design:
> http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html
>
> Unlike other designs out there, this one is very well done and has very
> little room for improvement, without increasing the price considerably.
>
> About the only things i would do different is to use two receiver
> channels, one fix connected at the TX source to be able to do a
> difference measurement between TX and the RX channels and thus
> improving precision. And the other would be to use a dual ADC
> with an FPGA for the data processing, again in order to increase
> performance.
>
> But as I wrote, both changes would increase complexity and price.
>
> Other than being a well thought through design, the website also
> explains all the big design choices and why this or that has been
> done instead of one of the many alternatives. That alone makes it
> worth reading, IMHO.
>
>             Attila Kinali
>
>
>
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Re: [time-nuts] DIY VNA design

[Richard (Rick) Karlquist]

Another great posting, Attila.

When I was with Agilent, we looked at all kinds of
simplified network analyzer architectures, and I
would have to say the author is really well informed.
One issue he doesn't seem to be aware of is that the
ADL5801, when driven single ended, has some quirks
below 100 MHz that I discovered experimentally.
(The data sheet is silent on this).  IMHO, it
would be worth 7 Euro's to use a balun, however,
I would like to know the part number of this
supposed component.  I am not so sure about MCL
actually covering 30 MHz to 6 GHz in the same
balun.  Sometimes their advertising is confusing,
and when they say .03-6 GHz baluns, they mean
that the range can be covered in several bands
by several model numbers.

Still, quite impressive work by an individual
practitioner.

Rick

On 8/20/2016 7:19 PM, Attila Kinali wrote:

Moin,

I stumbled over a new open hardware/source VNA design:
http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html

Unlike other designs out there, this one is very well done and has very
little room for improvement, without increasing the price considerably.

About the only things i would do different is to use two receiver
channels, one fix connected at the TX source to be able to do a
difference measurement between TX and the RX channels and thus
improving precision. And the other would be to use a dual ADC
with an FPGA for the data processing, again in order to increase
performance.

But as I wrote, both changes would increase complexity and price.

Other than being a well thought through design, the website also
explains all the big design choices and why this or that has been
done instead of one of the many alternatives. That alone makes it
worth reading, IMHO.

Attila Kinali




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[time-nuts] DIY VNA design

[Attila Kinali]

Moin,

I stumbled over a new open hardware/source VNA design:
http://hforsten.com/cheap-homemade-30-mhz-6-ghz-vector-network-analyzer.html

Unlike other designs out there, this one is very well done and has very
little room for improvement, without increasing the price considerably.

About the only things i would do different is to use two receiver
channels, one fix connected at the TX source to be able to do a
difference measurement between TX and the RX channels and thus
improving precision. And the other would be to use a dual ADC
with an FPGA for the data processing, again in order to increase
performance.

But as I wrote, both changes would increase complexity and price.

Other than being a well thought through design, the website also
explains all the big design choices and why this or that has been
done instead of one of the many alternatives. That alone makes it
worth reading, IMHO.

Attila Kinali



-- 
Malek's Law:
Any simple idea will be worded in the most complicated way.
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