DIY VNA design
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.
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
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 <richard@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
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.
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 <
richard@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
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.
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.
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 <orin.eman@gmail.com> 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 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 richard@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
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.
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.
[]
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-taylor@blueyonder.co.uk
Twitter: @gm8arv
On Sun, 21 Aug 2016 04:46:10 +0000 (UTC)
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...
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.
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 <orin.eman@gmail.com> 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 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 <richard@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
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 +0000 (UTC)
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...
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
On Sun, 21 Aug 2016 10:04:10 -0700
Alex Pummer alex@pcscons.com 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