Re: Measuring a 1/4 wave balanced line
#cables
Great! Thanks. Any google search I attempted lead me to the RSGB website, which was a dead end for me. I did realize the forums were right here on groups.io, duh.
|
Hello, All...
I recently had a need to measure an unknown matching transformer. As it was
in a sealed enclosure with noth but the wire terminal and coax connector
exposed, and I didn't want to damage the enclosure, I pulled out my trusty
NanoVNA.
All I knew about the "black box" was that it was used with a
10-12-15-17-20m EFHW wire antenna. That made me assume it would be
somewhere in the range of a 49:1 ratio.
I pulled out my decade resistance box and dialed in 2450 ohms (50 ohms x
49) and put that between the output wire terminal and ground. I then
connected the NanoVNA to the coax input.
I then played with the decade box until I got a flat response from the
NanoVNA and the needed resistance to get there was 2501 ohms. Technically,
that makes the matching network about 50:1 ratio.
All of this told me what I wanted to know, but I'm wondering if there would
be an easier, more direct way of getting there with the NanoVNA.
I'm good with the idea that I may have just stumbled onto the right answer
in my madness.
Take Care & 73
--
de KC6UFM
Charles
|
Re: Measuring a 1/4 wave balanced line
#cables
[image: image.png] This should get you started. Dave - WLEV On Sun, Aug 15, 2021 at 7:40 PM Lou W7HV via groups.io <louandzip= [email protected]> wrote: On Sun, Aug 15, 2021 at 12:26 PM, David Eckhardt wrote:
Owen's posts can also be accessed on the RSGB sites. I subscribe to both
the "antennas" and the "antennas research" sites from RSGB.
Did a quick search for RSGB sites as described but didn't have any luck.
Could you provide a link or more info to help find them?
TNX
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Re: Measuring S11 at input of RF power amplifier - could I calibrate "through" an attenuator?
On 8/15/21 12:37 PM, Roger Need via groups.io wrote: On Sat, Aug 14, 2021 at 09:14 AM, David Feldman wrote:
If I insert (example) 6 dB pad between nanovna S11 port and amplifier input
port, and calibrate the nanovna (open-short-load) at the "far" end of the pad,
what impact would this have on S11 measurements?
Here are some S11 measurements I did "calibrating out" a 10 dB and a 20 db attenuator. Measurement errors get worse as you increase the attenuation but 6 dB won't be bad at all.
/g/nanovna-users/message/18145
Roger What's the ripple in the measurement from? A reduced SNR would give a random error, not a periodic one, but maybe it's a manifestation of a phase bias that is contributing more or less depending on the reflected phase?
|
Re: Measuring S11 at input of RF power amplifier - could I calibrate "through" an attenuator?
On 8/15/21 12:06 PM, KENT BRITAIN wrote: How does the output load become part of the S11 measurement?
I agree you need it to keep the amp happy, but when you make your?amplitude and phase measurements on the antenna tuner, the load should?not be part of that.? ? ? Kent G8EMY on real amplifiers, with non zero S12, the load impedance does show up at the input - imagine an amplifier with S12 of -10 dB and a S11 of -100dB.? A total reflection at the output of the amp will make the S11 of the amplifier appear to be -10dB. With solid state stage gains for power amplifiers of 8-10dB, this isn't so unusual. As long as |S12|<|S21| the amplifier will probably be stable. And on a non-amplifier case, if you have two antennas that have any mutual coupling (or for which you hope there's negligible coupling), the impedance connected to the feedpoint of antenna 2 affects the measured impedance of antenna 1. I've been doing some measurements of just that - using only S11 measurements of the AUT.
|
This is what I get using an inductor (7 turns of RG58A through a toroid) and the component is connected to CH0 and calibrated: [image: afbeelding.png] You see the S11 |Z| graph is a straight line (when it is displayed logarithmic and the freqy axis also logarithmic). A mor eor less pure inductance will be a stright line going up (a capacitance a straight lien going down). And Marker1 is at around |Z|=94ohm (and in the Marker 1 info you see an 'Series X': 51.551uH. You can also see the S11 Serial L [H] graph where you can see the inductance is around 52uH. If I would have shown a larger freq. range, S11 Phase would have gone through 0 (aka resonance). So no extra component needed. Hope this helps. All the best, Victor Op zo 15 aug. 2021 om 11:59 schreef Victor Reijs via groups.io <pe1atn.victor.reijs@...>:
I think you need a low frequency to determine the inductance (as say you
know).Say between 10kHz and 200kHz? The log(|Z|) curve in a log(Freq)
should go up in a straight line (NanoVNA Saver can provide this log axis).
All the best,
Victor
Op zo 15 aug. 2021 om 01:29 schreef Bob Albert via groups.io <bob91343=
[email protected]>:
First put an adapter on the SMA connector and set up the calibration. Go
to Smith Chart. Select your frequency range. Short the test leads and see
how much residual inductance there is. Then connect the unknown. Move the
marker to whatever frequency you like and it will read out directly.
Bob
On Saturday, August 14, 2021, 02:58:37 PM PDT, Joe WB9SBD < nss@...>
wrote:
I have a NanoVNA-H4.
Using this, what is the best accurate way to measure the inductance of a
coil?
Joe WB9SBD
|
Re: 340 MHz Dipole - Calibration at Transmitter and Antenna Ends of Transmission Line
Dave - Thanks once again for all the information. I'll test the modification using the 1/8 wavelength frequency in SimSmith and see how it compares. That change also allows the method posted by John Gord to be checked at the same time. In that case the cable impedance can be read directly using the -jX value.
I won't be able to do anything more with the physical coax. As an alternative, I'm studying the various Smith Chart methods that measure coax impedance using SimSmith.
After comparing results with RG-58A/U, RG-213/U and a coax model with zero ohms DC resistance, it looks like DC resistance in coax cable reduces the accuracy of these measurement techniques.
I did notice something interesting yesterday. The capacitance value in the impedance rises to the left of your lower measurement point and it declines to the right. The capacitance value near the 3:00 o'clock position appears to be close to published capacitance per foot values. The frequency declines towards zero as you approach that point.
73, Kent
AA6P
|
Re: Measuring a 1/4 wave balanced line
#cables
On Sun, Aug 15, 2021 at 12:26 PM, David Eckhardt wrote:
Owen's posts can also be accessed on the RSGB sites. I subscribe to both
the "antennas" and the "antennas research" sites from RSGB.
Did a quick search for RSGB sites as described but didn't have any luck. Could you provide a link or more info to help find them? TNX
|
Re: Measuring S11 at input of RF power amplifier - could I calibrate "through" an attenuator?
On Sat, Aug 14, 2021 at 09:14 AM, David Feldman wrote: If I insert (example) 6 dB pad between nanovna S11 port and amplifier input
port, and calibrate the nanovna (open-short-load) at the "far" end of the pad,
what impact would this have on S11 measurements?
Here are some S11 measurements I did "calibrating out" a 10 dB and a 20 db attenuator. Measurement errors get worse as you increase the attenuation but 6 dB won't be bad at all. /g/nanovna-users/message/18145Roger
|
|
|
Joe, When measuring the inductance of a coil with a NanoVNA one needs to keep a few things in mind. The inductor will also have resistance and self capacitance. The self capacitance will affect the measurement so that you are actually measuring "apparent inductance". If the coil is made with ferrite material the permeability will change with frequency and hence so will the inductance. Most of the online turns calculators for ferrites are only a reasonable estimate at low frequencies and the coil will have lower inductance as the frequency increases. The NanoVNA is quite accurate but you need to have a proper test fixture in order to minimize the effect of stray inductance and capacitance as well as errors due to poor calibration. Using alligator clip or test grabber clips will yield poor results. It is easy to make a mistake or draw a false conclusion about a component's characteristics when using a VNA. This can be due to many factors including the following: - limitations of the NanoVNA hardware and software - limitations of the test jig - quality of calibration load and calibration method - excess lead length - misconceptions about the component under test - insufficient technical knowledge There was a lengthy post about this topic in this group a few months ago. I started it off and many knowledgeable users contributed to the discussion. You should find it helpful. /g/nanovna-users/topic/80744049?p=Created,,,20,1,0,0::recentpostdate%2Fsticky,,,20,2,240,80744049 Here is a post I made in that discussion about measuring inductors. A test jig that works well for HF is shown and some actual measurements are made comparing the NanoVNA to a LCR meter. /g/nanovna-users/topic/pitfalls_of_measuring/80744049?p=Created,,,20,1,20,0::recentpostdate%2Fsticky,,,20,2,240,80744049&jump=1 Roger
|
Re: Measuring S11 at input of RF power amplifier - could I calibrate "through" an attenuator?
How does the output load become part of the S11 measurement?
I agree you need it to keep the amp happy, but when you make your?amplitude and phase measurements on the antenna tuner, the load should?not be part of that.? ? ? Kent G8EMY
toggle quoted message
Show quoted text
On Sunday, August 15, 2021, 01:48:51 PM CDT, David Eckhardt <davearea51a@...> wrote: No....n o ....... N? O.....? ? ? I was dealing and referring to the INPUT which is what you requested! Yes, then read the combination looking back into the 50-ohm load and matching network which you have adjusted on the INPUT for minimum SWR. Please carefully read what I originally wrote. On Sun, Aug 15, 2021 at 6:30 PM KENT BRITAIN <WA5VJB@...> wrote: ? "Then use the Nano to read the impedance
of the tuner/dummy load?"
This configuration would be on the output of an amp, not the input.
Measurement of S22 and very often S12 can be very helpful as you know in
amp development and trouble shooting.? ? Oh the fun of finding out your 20
dB gain amp has an S12 of only 19 dB!? ? (On the very edge of becoming an
oscillator)
? ? On Sunday, August 15, 2021, 01:17:42 PM CDT, David Eckhardt <
davearea51a@...> wrote:
? I was addressing the INPUT as the requester!? Why would I feed an RF
source to the output???????????
Dave - W?LEV
On Sun, Aug 15, 2021 at 5:54 PM Jim Lux <jim@...> wrote:
On 8/15/21 10:04 AM, Joe wrote:
What about connecting the amplifier to a dummy load thru an antenna
tuner. Tune for minimum SWR. Then use the Nano to read the impedance
of the tuner/dummy load?
Joe That's more about measuring the amplifier's output impedance, I think
the OP is looking for amplifier input impedance.
Here's what's great about the NanoVNA - There's going to be people who
figure out how to make high power measurements with it, what sort of
"test set" is needed.? Maybe modified versions perhaps.
And someone is going to come up with clever inexpensive ways to do this
with "reasonable" accuracy.
But there's been a lot of discussion over the years about what the
actual output Z of a transmitter is. (often with long threads about
Thevenin matches, arguments about efficiency, the limitations of simple
models, etc.).? Hey, now we're close to being able to *measure* it, at
different output powers and into different loads.? This is way cool.
See, e.g., Maynard Wright's article in QEX a couple months ago.
--
*Dave - W?LEV*
*Just Let Darwin Work*
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Re: Measuring S11 at input of RF power amplifier - could I calibrate "through" an attenuator?
No....n o ....... N O..... I was dealing and referring to the INPUT
which is what you requested!
Yes, then read the combination looking back into the 50-ohm load and
matching network which you have adjusted on the INPUT for minimum SWR.
Please carefully read what I originally wrote.
toggle quoted message
Show quoted text
On Sun, Aug 15, 2021 at 6:30 PM KENT BRITAIN <WA5VJB@...> wrote: "Then use the Nano to read the impedance
of the tuner/dummy load?"
This configuration would be on the output of an amp, not the input.
Measurement of S22 and very often S12 can be very helpful as you know in
amp development and trouble shooting. Oh the fun of finding out your 20
dB gain amp has an S12 of only 19 dB! (On the very edge of becoming an
oscillator)
On Sunday, August 15, 2021, 01:17:42 PM CDT, David Eckhardt <
davearea51a@...> wrote:
I was addressing the INPUT as the requester! Why would I feed an RF
source to the output???????????
Dave - W?LEV
On Sun, Aug 15, 2021 at 5:54 PM Jim Lux <jim@...> wrote:
On 8/15/21 10:04 AM, Joe wrote:
What about connecting the amplifier to a dummy load thru an antenna
tuner. Tune for minimum SWR. Then use the Nano to read the impedance
of the tuner/dummy load?
Joe That's more about measuring the amplifier's output impedance, I think
the OP is looking for amplifier input impedance.
Here's what's great about the NanoVNA - There's going to be people who
figure out how to make high power measurements with it, what sort of
"test set" is needed. Maybe modified versions perhaps.
And someone is going to come up with clever inexpensive ways to do this
with "reasonable" accuracy.
But there's been a lot of discussion over the years about what the
actual output Z of a transmitter is. (often with long threads about
Thevenin matches, arguments about efficiency, the limitations of simple
models, etc.). Hey, now we're close to being able to *measure* it, at
different output powers and into different loads. This is way cool.
See, e.g., Maynard Wright's article in QEX a couple months ago.
--
*Dave - W?LEV*
*Just Let Darwin Work*
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
Re: Measuring S11 at input of RF power amplifier - could I calibrate "through" an attenuator?
On 8/15/21 11:17 AM, David Eckhardt wrote: I was addressing the INPUT as the requester! Why would I feed an RF
source to the output??????????? As noted, the OP was looking at inputs, but someone else suggested a way to measure outputs. My comment was on that. Why would you want to feed an RF source to an output? Because you wanted to measure the S22? (or perhaps the S12 as well). And you want to do that while the amplifier is amplifying another signal. This is a common question in phased arrays where the amplifiers don't have isolators on the output.? A HF over the horizon radar is a good example. Lots of mutual coupling among the antennas, each amplifier is fed with a different waveform for things like beam steering, and the waveform isn't a sinusoid, but is modulated so pulse compression can be used. This isn't easy <grin> Hams have historically not tended not to be interested in this, because the regulatory environment encourages "single amplifier at which we can measure the power output", and it's also complex to implement.? But, particularly in microwave area, it's exceedingly common - MIMO and all that.? For all we know, the clever design of the Starlink transceiver uses it.
|
Re: Measuring S11 at input of RF power amplifier - could I calibrate "through" an attenuator?
"Then use the Nano to read the impedance
of the tuner/dummy load?"
This configuration?would be on the output of an amp, not the input.
Measurement?of S22 and very often S12 can be very helpful as you know in amp?development?and trouble shooting.? ? Oh the fun of finding out your 20 dB gain amp?has an S12 of only 19 dB!? ? (On the very edge of becoming an oscillator)
toggle quoted message
Show quoted text
On Sunday, August 15, 2021, 01:17:42 PM CDT, David Eckhardt <davearea51a@...> wrote: I was addressing the INPUT as the requester!? Why would I feed an RF source to the output??????????? Dave - W?LEV On Sun, Aug 15, 2021 at 5:54 PM Jim Lux <jim@...> wrote: On 8/15/21 10:04 AM, Joe wrote:
What about connecting the amplifier to a dummy load thru an antenna
tuner. Tune for minimum SWR. Then use the Nano to read the impedance
of the tuner/dummy load?
Joe That's more about measuring the amplifier's output impedance, I think
the OP is looking for amplifier input impedance.
Here's what's great about the NanoVNA - There's going to be people who
figure out how to make high power measurements with it, what sort of
"test set" is needed.? Maybe modified versions perhaps.
And someone is going to come up with clever inexpensive ways to do this
with "reasonable" accuracy.
But there's been a lot of discussion over the years about what the
actual output Z of a transmitter is. (often with long threads about
Thevenin matches, arguments about efficiency, the limitations of simple
models, etc.).? Hey, now we're close to being able to *measure* it, at
different output powers and into different loads.? This is way cool.
See, e.g., Maynard Wright's article in QEX a couple months ago.
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Re: Measuring a 1/4 wave balanced line
#cables
Owen's posts can also be accessed on the RSGB sites. I subscribe to both the "antennas" and the "antennas research" sites from RSGB. Owen's posts are excellent and always technically and engineering wise sound. Our friends to the east in the UK and Germany have some sharp hams, far more so than here in the states (I won't go on that rant, again....???) . And, I probably should not post this, but the RSGB sites are far more open to expressing opinions; positive, negative, roasting, or flaming. I steer clear of such practices (mostly - I've been roasted a few times), but I have to occasionally smile at some of the humor from the other side of the small pond. And, I must confess some of the roasting and flaming is deserved. Dave - W?LEV On Sun, Aug 15, 2021 at 6:17 PM Roger Need via groups.io <sailtamarack= [email protected]> wrote: Some of you may be familiar with the blog of an Australia ham Owen Duffy.
He posts on a wide range of topics and is technically quite
knowledgeable. He "lurks" on this group and does not post here but does
comment on topics under discussion on his blog.
A recent post was about this topic. Readers might find it interesting.
Sadly many of his posts (like this one) make pejorative comments about
members of this group who he refers to as "online experts" and there is no
way to comment on his blog or offer any kind of rebuttal. One wonders why
he does not post directly in this group where a technical discussion. can
take place.
Roger
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Re: Measuring S11 at input of RF power amplifier - could I calibrate "through" an attenuator?
I was addressing the INPUT as the requester! Why would I feed an RF
source to the output???????????
Dave - W?LEV
toggle quoted message
Show quoted text
On Sun, Aug 15, 2021 at 5:54 PM Jim Lux <jim@...> wrote: On 8/15/21 10:04 AM, Joe wrote:
What about connecting the amplifier to a dummy load thru an antenna
tuner. Tune for minimum SWR. Then use the Nano to read the impedance
of the tuner/dummy load?
Joe That's more about measuring the amplifier's output impedance, I think
the OP is looking for amplifier input impedance.
Here's what's great about the NanoVNA - There's going to be people who
figure out how to make high power measurements with it, what sort of
"test set" is needed. Maybe modified versions perhaps.
And someone is going to come up with clever inexpensive ways to do this
with "reasonable" accuracy.
But there's been a lot of discussion over the years about what the
actual output Z of a transmitter is. (often with long threads about
Thevenin matches, arguments about efficiency, the limitations of simple
models, etc.). Hey, now we're close to being able to *measure* it, at
different output powers and into different loads. This is way cool.
See, e.g., Maynard Wright's article in QEX a couple months ago.
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
Re: Measuring a 1/4 wave balanced line
#cables
Some of you may be familiar with the blog of an Australia ham Owen Duffy.
He posts on a wide range of topics and is technically quite knowledgeable. He "lurks" on this group and does not post here but does comment on topics under discussion on his blog.
A recent post was about this topic. Readers might find it interesting.
Sadly many of his posts (like this one) make pejorative comments about members of this group who he refers to as "online experts" and there is no way to comment on his blog or offer any kind of rebuttal. One wonders why he does not post directly in this group where a technical discussion. can take place.
Roger
|
Re: Measuring S11 at input of RF power amplifier - could I calibrate "through" an attenuator?
On 8/15/21 10:04 AM, Joe wrote: What about connecting the amplifier to a dummy load thru an antenna tuner. Tune for minimum SWR. Then use the Nano to read the impedance of the tuner/dummy load?
Joe That's more about measuring the amplifier's output impedance, I think the OP is looking for amplifier input impedance. Here's what's great about the NanoVNA - There's going to be people who figure out how to make high power measurements with it, what sort of "test set" is needed.? Maybe modified versions perhaps. And someone is going to come up with clever inexpensive ways to do this with "reasonable" accuracy. But there's been a lot of discussion over the years about what the actual output Z of a transmitter is. (often with long threads about Thevenin matches, arguments about efficiency, the limitations of simple models, etc.).? Hey, now we're close to being able to *measure* it, at different output powers and into different loads.? This is way cool. See, e.g., Maynard Wright's article in QEX a couple months ago.
|
Hi David, but the capacitance of the internal windings of a chip inductor are usually unknown.Of course after you have measured the SRF, you can then calculate it.Kent(I have fought this problem for years with some EW Broadband amps)
toggle quoted message
Show quoted text
On Sunday, August 15, 2021, 12:41:12 PM CDT, David Eckhardt <davearea51a@...> wrote: If you know the capacitor value, calculating the inductance from the resonance formula is trivial for any calculator.? Just like the Grid Dipper! ? ? ? ? ? 2 ? ? ? ? f? ? =? 25330 / (L x C)? ? ? ? ? f in MHz? ? ? ? ? L in ?H? ? ? ? ? ? C in pF This is easily derived by setting up the requirement for resonance:? XL = XC? ? and plugging in the appropriate units. I would propose the inductance measurement would be most meaningful if measured at the required target frequency. Dave - W?LEV On Sun, Aug 15, 2021 at 5:30 PM Joe WB9SBD <nss@...> wrote: Hi Dave,
Ok I'll try both methods and see if it comes up with different answers.
Now is there anywhere a he he he "Video" or a written step by step etc,
on how to do the smith chart way?
Joe WB9SBD
On 8/15/2021 11:41 AM, David Eckhardt wrote:
Is everything these days a YouTube "presentation".? I'm not knocking what
is presented, as the theory is sound and is rather reminiscent of the setup
employed when measuring inductance with a grid dip oscillator, but a bit
more accurate.
Any of the NANOs can measure inductance (and capacitance) directly using
the Smith Chart option and the Cursors.? Once calibrated, the inductor is
connected across the source port directly, yes, both center pin and
backshell of the connector.? It will be in parallel with that port.? Once
configured, the value of the real part and the equivalent reactance of the
complex port (the inductor) can be easily read in the upper left of the
NANO display.? The NANOs can also be configured to simply display the
reactance of the complex part directly instead of the equivalent value of
the lumped inductor.? Again, just an absolutely wonderful instrument which
compares embarrassingly well to the (expensive) HP/Agilent/Keysite VNAs.
Dave - W?LEV
On Sun, Aug 15, 2021 at 1:59 PM Joe WB9SBD <nss@...> wrote:
I found this video,
It seems like maybe a better way?
Thoughts?
Joe WB9SBD
On 8/15/2021 4:59 AM, Victor Reijs wrote:
I think you need a low frequency to determine the inductance (as say you
know).Say between 10kHz and 200kHz? The log(|Z|) curve in a log(Freq)
should go up in a straight line (NanoVNA Saver can provide this log axis).
All the best,
Victor
Op zo 15 aug. 2021 om 01:29 schreef Bob Albert via groups.io
<bob91343=
[email protected]>:
? ? First put an adapter on the SMA connector and set up the calibration.? Go
to Smith Chart.? Select your frequency range.? Short the test leads
and
see
how much residual inductance there is.? Then connect the unknown.
Move
the
marker to whatever frequency you like and it will read out directly.
Bob
? ? ? On Saturday, August 14, 2021, 02:58:37 PM PDT, Joe WB9SBD <
nss@...>
wrote:
? ? I have a NanoVNA-H4.
Using this, what is the best accurate way to measure the inductance
of a
coil?
Joe WB9SBD
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Lou W7HV
Roger Need