Fantastic job.
I have practicly every manual for the NanoVNA H that I could get my hands on to learn the NanoVNA. Not to degrade the other manuals, but yours seem to be the most useful for a old beginner like me.
Thank you and all others who help us to learn and use the NanoVNA to its fullest.
Now, we need one like yours for the NanoSA.
Again thank you.
73's
Clyde Lambert KC7BJE
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Re: nanoVNA as TDR on coiled heliax?
On 11/8/20 12:17 PM, John AE5X wrote: Hello all,
I don't have much experience using TDR's in general and am wondering if they can accurately measure cable length if the cable is coiled rather than deployed in a more typical manner? At my work QTH we have a length of heliax on a big wooden spool and no one knows how much of it there is, nor can we easily count the number of coils on this stuff. It is quite rigid and we'd like to not have to unroll it.
Thanks/73,
that is the perfect use for a TDR.
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Re: nanoVNA as TDR on coiled heliax?
I am no expert, (I have only used TDR with Nanosaver on short lengths with multiple connections -every single connector showed up with a slight blip) but I see no reason for a TDR measurement not to work. It does not matter that the wire is coiled although there might be some uncertainty at the far end ; hopefully it is open circuit at the far cut end, but the last inch might be crushed. What you hope is that there is not a perfect 50 ohm load at the far end! You need to set the vna to the highest possible upper frequency for short lengths (1mm to a metre) but have the lowest start frequency for long lengths.
The biggest difficulty will be to get a decent connection to the heliax. I do not know how you connect Heliax to sma. I suppose very short wires soldered to the sma connection should be ok for the far end measurement. You might even get a clean enough signal to confirm that there is no damage somewhere on the coil.
Steve L
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nanoVNA as TDR on coiled heliax?
Hello all,
I don't have much experience using TDR's in general and am wondering if they can accurately measure cable length if the cable is coiled rather than deployed in a more typical manner? At my work QTH we have a length of heliax on a big wooden spool and no one knows how much of it there is, nor can we easily count the number of coils on this stuff. It is quite rigid and we'd like to not have to unroll it.
Thanks/73,
--
John AE5X
|
Martin can you send me this document
Tnx
--
Sent from my Android phone with GMX Mail. Please excuse my brevity.
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On 11/8/20, 02:44 "Martin J.K." <martin.svaco@...> wrote:
Thank you all for kind words and advice in this group and to email.
On page 8, in the text below the figure 13, should have been written
''on a scale of 20 ohms per VERTICAL division'' - thank you Ed.
The word ''CHANEL'' in figure 13 should be ''CHANNEL'' - thank you Bob.
Larry, thank you for your advice. I will try to expand the next version of
the Guide.
73
Martin 9A2JK
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Re: Touch screen not working right
The exact same case. While calibrating only "Y" axis is working. The horizontal "X" axis was always stuck at the very screen edge. I followed Bob's solution - re-solder the flex cable and now works like a charm. 73 de SV1ONK
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I too send you my thanks for an excellent tutorial document. Very nicely
done.
Two simple notes to consider adding:
- The firmware gives reasonable defaults for the scale and reference line
for many use cases, so you only need to set them if you need them to be
different.
- When you save a calibration, it also saves the display settings, so you
can easily recall the whole setup.
(I note these because the list of setup tasks for each measurement seems
long and maybe intimidating if I have to do them for every measurement -
but it's not nearly as bad as it seems.)
Stan KC7XE
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On Sun, Nov 8, 2020, 4:10 AM John <ve3ips@...> wrote: Martin your a Rockstar!
Now we need one for the TinySA
John VE3IPS
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Re: Help reading Antenna plots
Martin, you peak my interest / curiosity in making even more measurements on my system. In choosing what I have done with my 450-foot (137-meter) doublet is based on two things: 1) Results as measured on the HP 8753C VNA for each choke, and 2) Suppression of CM noise from the (new) home appliances with all their embedded SMPS's. You motivate me to make a few more measurements with everything in place with current probes (which I will have to make). I once had a piece of test equipment I made with a current probe on each of the two conductors of the open wire feeders as they left the shack. I could measure total current on each conductor, and ultimately 'sum' the results to obtain the expected zero with no CM current. Anything indicated with the 'sum' would be CM current. I need to make another just like that as the original was lost in a fire in 2012. Good suggestion! I shall also measure and present the inductive reactance of my chokes. I have actually done this, but not recorded values (bad engineer as I don't keep a rigorous 'engineering notebook'). Dave - W?LEV On Sun, Nov 8, 2020 at 2:36 PM Martin via groups.io <martin_ehrenfried= [email protected]> wrote: On Sat, Nov 7, 2020 at 08:27 PM, David Eckhardt wrote:
Just one I could dig up quickly. Most explanations of a balun simply
state
they are a 'transformer' (which they may or may not be) that bilaterally
transforms CM to DM. They do not dig into how they accomplish that
function.
Hi Dave,
Thanks for the links, unfortunately they only cover the cancellation of
Common Mode currents, and do not address the issue of reactive impedance,
and if it is desirable in a Common Mode Choke Balun.
I think the crux of the discussion is if it is better to have a common
mode choke with a predominantly resistive impedance to act as an absorptive
load for CM signals, or as a predominantly reactive load that is reflective
to CM signals.
Ideally it would be better to have a high enough value of resistive CM
impedance so that CM signals are blocked, are not dissipating significant
amounts of energy as waste heat, and are not creating unpredictable CM
standing waves elsewhere.
However you don't seem to be able to achieve this, as you are running high
power and seem to have a lot of CM to deal with, so you are resorting to
using type 2 'Iron Powder' because the CM impedance is primarily reactive,
and the material is no longer over-dissipating.
But this isn't dealing with what happens to the highly reactive CM
component that is reflected back from the balun. Simply because you are not
observing over-dissipation in the Balun, or RF in the shack, it doesn't
mean that the balun is actually working effectively, it maybe just moving
the problem, and the common mode RF could still be dissipated as heat
somewhere else in the antenna system.
I wonder if you have been able to make any comparative measurements with a
RF current probe along the feed line, in order to determine the
effectiveness of the Balun ?
Regards,
Martin - G8JNJ
-- *Dave - W?LEV* *Just Let Darwin Work*
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Re: Help reading Antenna plots
Indeed Martin, that's why I use a 31-core and not a 2-core for this frequency.
Enclosed is a a graph, measured by nanoVNA H3.2 for a 240-31 core and 15 windings of rg58 coax. (It's a CMC in my 3.5 - 7 - 10 MHz trap-dipole.)
Resonance is visible at 5 MHz but then there is the resistive part of the impedance that saves the day. ;-)
For the record, I did the same measurement with 15? turns of RG174 (the thin coax). Due to less capacitance between windings the resonance point goes up in frequency to just aroud 6 MHz.
73
Arie PA3A
Op 8-11-2020 om 15:46 schreef Martin via groups.io:
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On Sun, Nov 8, 2020 at 08:36 AM, Arie Kleingeld PA3A wrote:
Let's suppose you want a clean 500 ohm inductive impedance. A bit more than 31
windings on a T200-2 core will do that on 7MHz
Hi Arie,
I quickly wound some wire on a T200-2 'Iron powder' core.
Yes it does indeed produce an inductive reactance of around 500 Ohms at 7MHz, but it also has a very low value of resistive component, a self resonance at around 10MHz and has capacitive reactance above the self resonant frequency.
The bandwidth around resonance where the value of reactance exceeds 1,000 Ohms is only 6MHz wide, so it's only got a small frequency range over which it is likely to be effective. The range over which the resistive part exceeds 1,000 Ohms is less than 0.5MHz.
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Re: Help reading Antenna plots
On Sun, Nov 8, 2020 at 08:36 AM, Arie Kleingeld PA3A wrote:
Let's suppose you want a clean 500 ohm inductive impedance. A bit more than 31
windings on a T200-2 core will do that on 7MHz
Hi Arie, I quickly wound some wire on a T200-2 'Iron powder' core. Yes it does indeed produce an inductive reactance of around 500 Ohms at 7MHz, but it also has a very low value of resistive component, a self resonance at around 10MHz and has capacitive reactance above the self resonant frequency. The bandwidth around resonance where the value of reactance exceeds 1,000 Ohms is only 6MHz wide, so it's only got a small frequency range over which it is likely to be effective. The range over which the resistive part exceeds 1,000 Ohms is less than 0.5MHz. -- Regards, Martin - G8JNJ
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Re: Help reading Antenna plots
On Sat, Nov 7, 2020 at 08:27 PM, David Eckhardt wrote:
Just one I could dig up quickly. Most explanations of a balun simply state
they are a 'transformer' (which they may or may not be) that bilaterally
transforms CM to DM. They do not dig into how they accomplish that
function.
Hi Dave, Thanks for the links, unfortunately they only cover the cancellation of Common Mode currents, and do not address the issue of reactive impedance, and if it is desirable in a Common Mode Choke Balun. I think the crux of the discussion is if it is better to have a common mode choke with a predominantly resistive impedance to act as an absorptive load for CM signals, or as a predominantly reactive load that is reflective to CM signals. Ideally it would be better to have a high enough value of resistive CM impedance so that CM signals are blocked, are not dissipating significant amounts of energy as waste heat, and are not creating unpredictable CM standing waves elsewhere. However you don't seem to be able to achieve this, as you are running high power and seem to have a lot of CM to deal with, so you are resorting to using type 2 'Iron Powder' because the CM impedance is primarily reactive, and the material is no longer over-dissipating. But this isn't dealing with what happens to the highly reactive CM component that is reflected back from the balun. Simply because you are not observing over-dissipation in the Balun, or RF in the shack, it doesn't mean that the balun is actually working effectively, it maybe just moving the problem, and the common mode RF could still be dissipated as heat somewhere else in the antenna system. I wonder if you have been able to make any comparative measurements with a RF current probe along the feed line, in order to determine the effectiveness of the Balun ? Regards, Martin - G8JNJ
|
Martin your a Rockstar!
Now we need one for the TinySA
John VE3IPS
|
Re: [nanovna-f] RETURN LOSS TO SWR CHART
Roger I was very fortunate in that my second job out of college (I got a BS in electrical engineering) was with HP. Back when HP was the instrumentation company. In those days (1982) I doubt anyone would disagree that HP was THE premier designer of RF test equipment. VERY active in everything RF.
As part of the training for sales people, so we could intelligently talk with our customers, they spent 9 weeks, in 3, 3 week segments, teaching us the basics of rf and of their instruments.
While much of what I learned has been relegated to the dust bin in my brain, a few things remain. One was that return loss was always positive. If you do the math this will be born out. If you just think about it, its a ratio of incident vs reflected rf (or maybe the other way around. I just don't recall). A ratio of two rf power levels should always be positive. But again, do the math.
Sure many many folks make it negative. Many, in their explanation, first say one thing then later in their article, the other. Of course confusing! And some conflate return loss with insertion loss. But, insertion loss will also always be positive so I've not understood that one.
Anyway, as you said, its an argument that's been around forever. And, one side will always be wrong :)
Ron
N4XD
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Yes very well done Martin !
People always need help and info on how best to use the VNA's, especially when they are new to the VNA area, which we all are (hobby/pro's alike) to start with.
|
Thank you all for kind words and advice in this group and to email.
On page 8, in the text below the figure 13, should have been written
''on a scale of 20 ohms per VERTICAL division'' - thank you Ed.
The word ''CHANEL'' in figure 13 should be ''CHANNEL'' - thank you Bob.
Larry, thank you for your advice. I will try to expand the next version of the Guide.
73
Martin 9A2JK
|
Re: Help reading Antenna plots
Very interesting discussion on the CMC.
Concentrating on the needed Z / X / R for a good reflection of the common mode currents.
Let's suppose you want a clean 500 ohm inductive impedance. A bit more than 31 windings on a T200-2 core will do that on 7MHz. That's a lot of windings, even on a T200 core. You'll need 22 windings on 14 MHz, still a lot.
For 1.8 - 10 MHz I use 31 cores.
73
Arie PA3A
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Martin:
What a great, well-written, and extremely useful document!
Thank you very much for taking the time and effort to create it, and then to share it with all of us.
Take Care & 73
de KC6UFM
Charles
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On 11/6/20 8:41 AM, Martin J.K. wrote: I have uploaded file in files section of this group:
Absolute Beginner's Guide to The NanoVNA.
Comments are welcomed here or to my email: 9a2jk _at_ hamradio.hr
As English is not my native language any advice regarding the language would be appreciated too.
Martin 9A2JK
|
Re: Help reading Antenna plots
I believe so. I pulled that picture off Amazon. As far as I know, it's
still available as a price was given.
Dave - W?LEV
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Show quoted text
On Sun, Nov 8, 2020 at 2:24 AM EB4APL <eb4apl@...> wrote: Do they still sell this kit? I bought one in a trip to USA in 1976!
Ignacio EB4APL
El 07/11/2020 a las 18:25, David Eckhardt escribió:
With a current balun or CM choke, it is the reactance (inductance) that is
mostly responsible for the balun action. In the case of the choke balun,
beads installed along the coax at the feed with 31 or 43 material, they
form a reflective 'filter'. There is some absorption, but most of the
action is due to reflection from the inductive reactance they form
installed on a conductor. As such, they form a high-Z isolation point
between the feeder and the antenna center, assuming they are installed at
the feedpoint of the doublet. In the case of the CM choke, the common mode
currents are reflected by the inductive reactance of the windings as with
the current balun and the balance of current between the two conductors is
forced through induced opposing magnetic currents within the cone. This is
the reason I prefer the CM choke for the purpose. In either case, the
common mode current is reflected to a large extent by the inductive
reactance back where it originated. Installation of a balun at the
feedpoint of a doublet does not make the CM currents go away, it just
establishes a 'fence' for those currents between non-antenna associated
currents (on the outside of the feedline) and the radiating structure.
I can assure you the core Amidon sells with their balun kit is a red core,
Typie 2 material:
[image: image.png]
Ferrites designed to introduce loss or absorption are good EMC/RFI
suppression devices. In the case of these ferrites, current is induced
into the ferrite structure where resistive losses to the induced magnetic
currents turn that energy to heat. These ferrite structures become rather
hot when used in the balun application for transmit energy.
If the balun action of the various cores were absorptive, they why are
'good' baluns specified as having , for example, 1000 ohms series
'resistance' at the lowest frequency of interest (or at least 5X the system
impedance). This should be specified as +j1000 to be correct. It is the
reflection of the CM currents that this high-Z addresses, not the
absorption of CM energy. If absorption were the requirement, then why the
higher +jX for better balun performance?
Dave - W?LEV
--
El software de antivirus Avast ha analizado este correo electrónico en
busca de virus.
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
Re: Help reading Antenna plots
Do they still sell this kit? I bought one in a trip to USA in 1976!
Ignacio EB4APL
toggle quoted message
Show quoted text
El 07/11/2020 a las 18:25, David Eckhardt escribió: With a current balun or CM choke, it is the reactance (inductance) that is
mostly responsible for the balun action. In the case of the choke balun,
beads installed along the coax at the feed with 31 or 43 material, they
form a reflective 'filter'. There is some absorption, but most of the
action is due to reflection from the inductive reactance they form
installed on a conductor. As such, they form a high-Z isolation point
between the feeder and the antenna center, assuming they are installed at
the feedpoint of the doublet. In the case of the CM choke, the common mode
currents are reflected by the inductive reactance of the windings as with
the current balun and the balance of current between the two conductors is
forced through induced opposing magnetic currents within the cone. This is
the reason I prefer the CM choke for the purpose. In either case, the
common mode current is reflected to a large extent by the inductive
reactance back where it originated. Installation of a balun at the
feedpoint of a doublet does not make the CM currents go away, it just
establishes a 'fence' for those currents between non-antenna associated
currents (on the outside of the feedline) and the radiating structure.
I can assure you the core Amidon sells with their balun kit is a red core,
Typie 2 material:
[image: image.png]
Ferrites designed to introduce loss or absorption are good EMC/RFI
suppression devices. In the case of these ferrites, current is induced
into the ferrite structure where resistive losses to the induced magnetic
currents turn that energy to heat. These ferrite structures become rather
hot when used in the balun application for transmit energy.
If the balun action of the various cores were absorptive, they why are
'good' baluns specified as having , for example, 1000 ohms series
'resistance' at the lowest frequency of interest (or at least 5X the system
impedance). This should be specified as +j1000 to be correct. It is the
reflection of the CM currents that this high-Z addresses, not the
absorption of CM energy. If absorption were the requirement, then why the
higher +jX for better balun performance?
Dave - W?LEV
--
El software de antivirus Avast ha analizado este correo electrónico en busca de virus.
|
Re: RETURN LOSS TO SWR CHART
Excellent. Thanks for posting link. And the chart got it right: return loss is always a positive number......unless their is gain in the device being measured.
Ron
N4XD
|
Clyde Lambert
sv1onk
Arie Kleingeld PA3A
John