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Hi all,
what measurements could be improved, or what additional measurements can be
done if using an external RF bridge, like this one:
[image: image.png]
I've read a lot of messages from the group and some wiki files, I've seen
the bridge mentioned but I still can't figure out if it would be an useful
addition to NanoVNA.
I suspect using the bridge would improve measurement of high impedance if
using a reference higher than 50 ohm.
Any info or examples are welcomed.
Thank you,
73 YO2NAA
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Hi YO2NAA - what measurements could be improved, or what additional measurements can be
done if using an external RF bridge, like this one: Funny that you show a blue one; if not directly from transverters-store.com, then probably a bad clone. Specifically, mine from eBay had paired 100 Ohm resistors to obtain 50 Ohms, but one of each was not connected. I've read a lot of messages from the group and some wiki files, I've seen
the bridge mentioned but I still can't figure out if it would be an useful
addition to NanoVNA.
I suspect using the bridge would improve measurement of high impedance
if using a reference higher than 50 ohm. Those unconnected 100 Ohm resistors make this work better for higher impedances, provided that a higher reference value is also employed and coax wiring is corrected. /g/nanovna-users/message/7205Any info or examples are welcomed. One challenge for use with nanoVNA is that I don't know any software that directly supports calibrated S11 measurement by CH1, which is wanted when using an external bridge.
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Its a way to permit using attenuation where you need it
and allow for gain as needed.
I can be used with a different reference such as 75 ohms (any actually)
for systems that are not 50 ohms to make measurements.
An example using that bridge is measuring a radios input impedance
where a very small signal may over load the radio.
If you put a attenuator on port 0 (s11) the return is also attenuated
and the results are hard to discern.
With the bridge you can attenuate the output and see the returned
signal from the radio input using port2 (s21) and if the signal is
weak one can add an amplifier (suitable type) at the input to PORT2.
There are other measurements that may require that as well
for example at higher powers.
The basic instrument is very flexible but the basis of it is a
RF source that has a matching detector that can present
phase and amplitude information.
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Thank you Oristo and KB1GMX for the info, much clearer now.
The picture of the bridge is indeed the original from transverters-store
<>, mine is on the way and will be a green
one, from ebay (60dbmco from Ukraine).
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Show quoted text
On Sun, Dec 1, 2019 at 9:10 PM aparent1/kb1gmx <kb1gmx@...> wrote: Its a way to permit using attenuation where you need it
and allow for gain as needed.
I can be used with a different reference such as 75 ohms (any actually)
for systems that are not 50 ohms to make measurements.
An example using that bridge is measuring a radios input impedance
where a very small signal may over load the radio.
If you put a attenuator on port 0 (s11) the return is also attenuated
and the results are hard to discern.
With the bridge you can attenuate the output and see the returned
signal from the radio input using port2 (s21) and if the signal is
weak one can add an amplifier (suitable type) at the input to PORT2.
There are other measurements that may require that as well
for example at higher powers.
The basic instrument is very flexible but the basis of it is a
RF source that has a matching detector that can present
phase and amplitude information.
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I do not accept private email due to forum scraping groups.io
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Good morning, and thank you for the add.
I understand the original designer is here, and the nanoVNA is available from him?
Thank you again,
Dave AB5S
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This is a self contained measurement device, A Bridge. The vna is not required although it could be used to replace the voltmeter or SA.
The bridge output provides a null in output voltage and the bridge Zo set by the loaded Tline is 50 ohms.
The bridge ports are source input, could be ch0 of the vna or any other source, term port 50 ohm, a DUT port and Detector port. Thats it. So the vna is not required or necessary. So not sure what was the intent on using this bridge?
Alan
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For those brave enough to try octave I have here an implementation in octave of the same calibration routine that is inside nanoVNA-saver. You only have to import the three measurements from CH1 (port 2) of Short, Open and Load using the external bridge and the calib.m routine will calculate the calibration. You can then use CH1 (port 2) to do S11 measurements by applying this formula y = ((m) .- ed) ./ ((es .* (m)) .- et); where y = corrected data m = measured data -- NanoVNA Wiki: /g/nanovna-users/wiki/homeNanoVNA Files: /g/nanovna-users/filesErik, PD0EK
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On Mon, Dec 2, 2019 at 08:21 AM, <erik@...> wrote:
"... using the external bridge and the calib.m routine will calculate the calibration.
You can then use CH1 (port 2) to do S11 measurements by applying this formula
y = ((m) .- ed) ./ ((es .* (m)) .- et);
where
y = corrected data
m = measured data"
=========================================================
Eric I have some questions if you don't mind answering:
1. Did you also use Octave to directly import the CH1 data?
2. Was the test set-up identical to the photo Oristo posted in his reply?
3. How accurate did you find this test method using references other than 50 ohms (75, 1000, etc) ?
I haven't purchased one of these bridges yet, but it would be an interesting project to translate your Octave code to Python to directly collect the calibration and port 1 data, apply the corrections in code, and plot/save the corrected results. It would be another way of increasing the utility of the NanoVNA.
- Herb
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Hi alan what was the intent on using this bridge I got mine to use with SDR and RF noise generator, but guessed that it might be better than nanoVNA internal bridge, which turns out to be good enough (and much easier) for my measurements, so far.. It is easier and less risky to hack this external bridge for greater than 50 Ohms. FWIW, even though nanoVNA may be poor for resistance > 1k Ohms, it works credibly by itself for e.g. capacitance down to 5 pF or so at fairly low frequencies (.e.g 10MHz). Also, FWIW, nanoVNA direct CH0 output is low enough for checking e.g. capacitive loading of moving magnet phono preamp inputs and cabling. Many MM cartridges want < 200pF load, and many MM preamp inputs have already 100pF, and too few 1m audio cables are < 100pF, not including tonearm wiring. RG-6 with F to RCA adapters is an easy/cheap way to reduce capacitance..
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On Mon, Dec 2, 2019 at 09:47 AM, hwalker wrote:
Eric I have some questions if you don't mind answering:
1. Did you also use Octave to directly import the CH1 data?
I use a small octave scrip to import a touchstone files in rectangular format. You do have to replace the '!' in the input file with '#' but than all you need is But you could also use octave to load the output of a 'data' command p = "nanoVNA" #set the load path f=load("-ascii",[p "\\" "Load.s2p.data"]); #this will load the s2p file into the matrix f skipping all comment lines global fr=f(:,1); # read the frequency table from the matrix global L=complex(f(:,2),f(:,3)); # read the real/imag data point from the S11 from the matrix 2. Was the test set-up identical to the photo Oristo posted in his reply? Yes CH0 as RF source, and CH1 connected to the bridge output 50ohm to the ref en SOL to the load 3. How accurate did you find this test method using references other than 50 ohms (75, 1000, etc) ? Did not test other references -- NanoVNA Wiki: /g/nanovna-users/wiki/homeNanoVNA Files: /g/nanovna-users/filesErik, PD0EK
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On Mon, Dec 2, 2019 at 09:47 AM, hwalker wrote:
but it would be an interesting project to translate your Octave code to Python
The octave code is a direct translation of the python code in nanoVNA-saver. If you need python than go look at nanoVNA-saver or ask Rune to enable the measurement of calibration input from CH1 instead of CH0, should be rather simple to implement. -- NanoVNA Wiki: /g/nanovna-users/wiki/homeNanoVNA Files: /g/nanovna-users/filesErik, PD0EK
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On Mon, Dec 2, 2019 at 09:56 AM, <erik@...> wrote:
"How accurate did you find this test method using references other than 50 ohms (75, 1000, etc) ?
Did not test other references"
===============================================================================
Got that Erik. For 50 ohms did you get more accurate measurement results with the external bridge, or just a more accurate results over a wider range?
- Herb
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Very good Oristo. Makes sense. I built a tandem coupler prior to getting the vna. Same idea as you outlined. This coupler is very interesting unit as it shows a directivity at HF of nearly 60 dB. Using a signal generator and a portable Oscope it was quite good at capturing mag and phase of the reflection coefficient. Its design is flexible and hence may be a good candidate for a Zo other than 50 ohm.
Alan
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I've found for higher load resistance greater than 1000 ohms
the bridge with a reference leg closer to the target made for far
better accuracy. Ran into that measuring loops at 10mhz
and up.
50 ohms is standard as most of the world is 50 ohms, or maybe 75.
However I have a set of references built up over the years of suitable
high stability resistors and capacitors for years back when a VNA
was a nice idea, for the rich.
I'd have to dig but HP/Agilent had a seris of notes for making
measurements that would be at the limits for the big box VNA/PNAs.
Allison
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I've found for higher load resistance greater than 1000 ohms
the bridge with a reference leg closer to the target made for far
better accuracy. These US$10 bridges can be fairly easily hacked to increase R of all 3 fixed legs.
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I want to purshase a bridge. Are there any differences between the green and blue versions?
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On December 2, 2019 at 4:02 PM Oristo < ormpoa@... > wrote:
I've found for higher load resistance greater than 1000 ohms
the bridge with a reference leg closer to the target made for far
better accuracy.
These US$10 bridges can be fairly easily hacked to increase R of all 3
fixed legs.
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On Tue, Dec 3, 2019 at 07:37 AM, n2msqrp wrote:
I want to purshase a bridge. Are there any differences between the green and blue versions?
================================================================================
You can follow the rest of the discussion under this topic by pressing the <View All 16 Messages In Topic> button. Basically it was reported in early messages that the blue version is a poorly assembled clone. The green one maybe a clone also but at least it is assembled correctly. The real unit can be ordered directly from .
- Herb
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Thanks for the information.
Mike N2MS
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On December 3, 2019 at 11:14 AM hwalker <herbwalker2476@...> wrote:
On Tue, Dec 3, 2019 at 07:37 AM, n2msqrp wrote:
I want to purshase a bridge. Are there any differences between the green and blue versions?
================================================================================
You can follow the rest of the discussion under this topic by pressing the <View All 16 Messages In Topic> button. Basically it was reported in early messages that the blue version is a poorly assembled clone. The green one maybe a clone also but at least it is assembled correctly. The real unit can be ordered directly from .
- Herb
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I got a '403 forbidden message' at the site you listed.
Doug
"The difference between stupidity and genius is that genius has its limits."
Albert Einstein
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Show quoted text
-----Original Message-----
You can follow the rest of the discussion under this topic by pressing the
<View All 16 Messages In Topic> button. Basically it was reported in early
messages that the blue version is a poorly assembled clone. The green one
maybe a clone also but at least it is assembled correctly. The real unit
can be ordered directly from .
- Herb
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On Mon, Dec 2, 2019 at 10:44 AM, hwalker wrote:
For 50 ohms did you get more accurate measurement results with the external
bridge
I did use the octave code for nanoVNA experiments. It just happens you can use the same calibration routines for an external bridge. As a consequence I did not perform any tests on an external bridge with the nanoVNA However I use the green eBay bridge in my 3GHz VNA and it works very well. up to 3GHz -- NanoVNA Wiki: /g/nanovna-users/wiki/homeNanoVNA Files: /g/nanovna-users/filesErik, PD0EK
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Oristo
David Stinson