The best and sound information I've located in a single source can be found
at the following URL. Open the 'balun' presentation. You will come away
with a wealth of good sound engineering knowledge.
Dave - W?LEV
toggle quoted message
Show quoted text
On Thu, Dec 24, 2020 at 5:00 PM John <ve3kkqve3kkq@...> wrote: Hi Kevin,
The choke folks are correct. This choke is used to stop/reduce the amount
of RF on the shield of the coax traveling down the coax into the shack.
Some folks will put a choke at the antenna and the shack end.
Do a Google search on common mode chokes, you'll get plenty to read.
GL.
Stay safe, wear a mask.
John
VE7KKQ
On Thu, Dec 24, 2020 at 5:22 AM AllassoPraise <allassopraise@...>
wrote:
I have seen desktop antenna/coax assemblies (such as for an SDR) that
take the (thin) coax cable and wrap it around a small toroid about 3
or 4 times, close to the antenna. I understand this is to keep the
shield of the coax from radiating.
I have tried to find information on the construction of these, but not
much comes up that is specific, making it seem like this isn't an
exact science, just "wrap a few turns around a toroid." Also, I have
heard them referred to as chokes and baluns, although others say they
do not function as a balun, only a choke.
Can anyone fill me in on this? And are there considerations to be
taken into account regarding the size of the toroid and the number of
wraps?
Also can this principle be used effectively for larger outdoor
antennas with larger coax, such as RG58 size?
Kevin
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
Hi Kevin, The choke folks are correct. This choke is used to stop/reduce the amount of RF on the shield of the coax traveling down the coax into the shack. Some folks will put a choke at the antenna and the shack end. Do a Google search on common mode chokes, you'll get plenty to read. GL. Stay safe, wear a mask. John VE7KKQ On Thu, Dec 24, 2020 at 5:22 AM AllassoPraise <allassopraise@...> wrote: I have seen desktop antenna/coax assemblies (such as for an SDR) that
take the (thin) coax cable and wrap it around a small toroid about 3
or 4 times, close to the antenna. I understand this is to keep the
shield of the coax from radiating.
I have tried to find information on the construction of these, but not
much comes up that is specific, making it seem like this isn't an
exact science, just "wrap a few turns around a toroid." Also, I have
heard them referred to as chokes and baluns, although others say they
do not function as a balun, only a choke.
Can anyone fill me in on this? And are there considerations to be
taken into account regarding the size of the toroid and the number of
wraps?
Also can this principle be used effectively for larger outdoor
antennas with larger coax, such as RG58 size?
Kevin
|
Re: Saving Measurement from antenna
Thanks to all who replied! I will look for the versions with the SD slot & see if the android solution will work with my hardware.
Hope all have a blessed new year!
Joe - W4RYW
|
covers the setup nicely.
--
Doug, K8RFT
|
Re: NanoVNA Function-Oriented Cheat Sheet
There's lots of documentation and guides in the group WIKI. Also, check in the "FILES" section.
There's also
--
Doug, K8RFT
|
On Thu, Dec 24, 2020 at 09:11 AM, DougVL wrote: Oops!
touch "FORMAT" and then touch "R+jX"
However, I'd forgotten, but not all firmware versions have "R+jX". Many have choices such as "REAL" and "IMAGINARY". I liked having the R+jX. -- Doug, K8RFT
|
On 12/24/20 5:21 AM, AllassoPraise wrote: I have seen desktop antenna/coax assemblies (such as for an SDR) that
take the (thin) coax cable and wrap it around a small toroid about 3
or 4 times, close to the antenna. I understand this is to keep the
shield of the coax from radiating.
I have tried to find information on the construction of these, but not
much comes up that is specific, making it seem like this isn't an
exact science, just "wrap a few turns around a toroid." Also, I have
heard them referred to as chokes and baluns, although others say they
do not function as a balun, only a choke.
Can anyone fill me in on this? And are there considerations to be
taken into account regarding the size of the toroid and the number of
wraps?
Also can this principle be used effectively for larger outdoor
antennas with larger coax, such as RG58 size? yes.. See this writeup by Jim K9YC - There are configurations that work better or worse, and core materials that work better or worse at different frequencies. For example the ubiquitous little EMI suppression cores you see on keyboards, cables, etc. are optimized for VHF frequencies.
|
Re: NanoVNA Function-Oriented Cheat Sheet
IMSAI GUY on Youtube is not nearly as smooth as Alan but he breaks things down so that a 3rd grader can understand.
Most of us will us a NanoVNA for an antenna Analyzer here is his short video to measure SWR
SWR:
Measuring filters:
NANOVNA Coax Velocity Factor and Coax Length
Most of his videos are less than 10 minutes
|
I have a NanoVNA-H which I just updated the firmware yesterday from the 0.2.xxx version which came with it to the latest Dislord version, 1.0.45.something.
First thing, before you do anything else, is to refer to the "Upgrade NanoVNA use DFU" at .
The .rar file is a compressed file, similar to a ZIP file. In it there are files for the NanoVNA-H and NanoVNA-H4.
When I followed the directions on that page, everything went great and I successfully upgraded my Firmware.
Good luck.
|
Wind your transformer in whatever configuration you are going with (I chose a 64:1 3T primary and 21T secondary). ======== That is wrong. 21/3 = 7, so the impedance transformation ratio is 7 x 7 = 49, i.e. 49:1 To have a 64:1 impedance transformer you need a 8:1 turns ratio, in other words, e.g., 3T primary and 24T secondary. -- /*73 Alberto I2PHD* <<< >>>/
|
A common mode choke made by wrapping coax feeder through a toroid is directly equivalent to a 1:1 Guanella "balun". The term balun is in quotes because, although coaxial cable is clearly an unbalanced feeder, the output of such an arrangement is not so much balanced to ground/earth, as effectively free to float. With a dipole antenna, and an effective balun/choke, then the dipole will inherently tend to be balanced, and the feeder will tend to be unbalanced.
What makes this possible is the impedance of the inductor formed by the turns through the toroid. What also makes this possible is the impedance of the feeder through the toroid. Since it is the same feeder, and the impedance transformation is 1:1, all is well. This arrangement is Guanella's 1:1 [wideband] transmission line transformer.
Depending on just how deep you wish to go, and where you are starting from in relation to technical knowledge, then putting "transmission line transformer" in your favourite search engine would be a good place to start! *Beware*: especially in Radio Amateur circles, the term "balun" is often used very loosely. Sometimes comments are made that are at variance to a clear understanding of basic electrical theory. YMMV, of course.
HTH, 73, Stay Safe,
Robin, G8DQX
toggle quoted message
Show quoted text
On 24/12/2020 13:30, Dragan Milivojevic wrote: Common mode choke, literally thousands of pages
out there dedicated to the topic. Good start for ham use:
On Thu, 24 Dec 2020 at 14:22, AllassoPraise <allassopraise@...> wrote:
I have seen desktop antenna/coax assemblies (such as for an SDR) that
take the (thin) coax cable and wrap it around a small toroid about 3
or 4 times, close to the antenna. I understand this is to keep the
shield of the coax from radiating.
I have tried to find information on the construction of these, but not
much comes up that is specific, making it seem like this isn't an
exact science, just "wrap a few turns around a toroid." Also, I have
heard them referred to as chokes and baluns, although others say they
do not function as a balun, only a choke.
Can anyone fill me in on this? And are there considerations to be
taken into account regarding the size of the toroid and the number of
wraps?
Also can this principle be used effectively for larger outdoor
antennas with larger coax, such as RG58 size?
Kevin
|
On Fri, Dec 18, 2020 at 07:17 AM, jim pat wrote:
the impedance real and imaginary
You can set the property (type of value) displayed by each of the 4 traces. Touch "MENU" , touch "TRACE", touch whichever color/channel you want to show the ' the impedance real and imaginary 'j on, then "BACK", touch "FORMAT" and then touch "R+jX" This is from the user guide at For more help, try some of the many youtube videos. -- Doug, K8RFT
|
Re: NanoVNA Function-Oriented Cheat Sheet
I endorse this comment fully!
I have worked with VNAs on and off in my working life for the last ten years or so, and I only wish I'd seen this presentation ten years ago!
It is the most succinct explanation of VNAs in general, and the "new" NanoVNA in particular. Worth viewing again and again until as much knowledge as you can handle sinks in!
It's probably working your way through the other G-QRPClub videos if you have time, there's some seriously good stuff in there!
73
Martin - G4FUI
|
Hi everyone new to this group . Happy Xmas everyone.
wonder can someone out there help.
im going to upate firmwear on my device.
version at the moment is 0.2.2-1 looking
here on the group im not sure if 1.0.3.9 rar file is the
correct file i have all softwear ready to go. but i get the scared
feeling if something goes wrong lol ive changed the rar file to dfu file
i know its a matter of clicking and thats it but just wanted some adivce
before i go ahead kind regards steve
|
Re: Saving Measurement from antenna
The Android NanoVNA app also works with my old 2.8 inch "not-H4" early clone that I bought in October, 2018 (if I remember correctly). That was about 6 months after NanoVNAs became available. It would now be called an 'H2', but back then it was 'the only'. I think I've read that Hugen also created that app.
There are now versions of the NanoVNA with a micro-SD card holder for storing measurement data, too. Search the group postings for more information, and for information about adding Bluetooth communication to the Nano. These features are developed by users, not manufacturers, although I think that Hugen has begun incorporating the memory card slot in some versions now being sold. Not the -F, though - that's from BH5NU, not from Hugen, and uses different hardware and different firmware. (I have a -F too. It's great!)
--
Doug, K8RFT
|
Common mode choke, literally thousands of pages
out there dedicated to the topic. Good start for ham use:
toggle quoted message
Show quoted text
On Thu, 24 Dec 2020 at 14:22, AllassoPraise <allassopraise@...> wrote: I have seen desktop antenna/coax assemblies (such as for an SDR) that
take the (thin) coax cable and wrap it around a small toroid about 3
or 4 times, close to the antenna. I understand this is to keep the
shield of the coax from radiating.
I have tried to find information on the construction of these, but not
much comes up that is specific, making it seem like this isn't an
exact science, just "wrap a few turns around a toroid." Also, I have
heard them referred to as chokes and baluns, although others say they
do not function as a balun, only a choke.
Can anyone fill me in on this? And are there considerations to be
taken into account regarding the size of the toroid and the number of
wraps?
Also can this principle be used effectively for larger outdoor
antennas with larger coax, such as RG58 size?
Kevin
|
I have seen desktop antenna/coax assemblies (such as for an SDR) that
take the (thin) coax cable and wrap it around a small toroid about 3
or 4 times, close to the antenna. I understand this is to keep the
shield of the coax from radiating.
I have tried to find information on the construction of these, but not
much comes up that is specific, making it seem like this isn't an
exact science, just "wrap a few turns around a toroid." Also, I have
heard them referred to as chokes and baluns, although others say they
do not function as a balun, only a choke.
Can anyone fill me in on this? And are there considerations to be
taken into account regarding the size of the toroid and the number of
wraps?
Also can this principle be used effectively for larger outdoor
antennas with larger coax, such as RG58 size?
Kevin
|
Hey Pete,
Indeed it is a 1:49 after all... I didn't catch that when I posted. My EFHW started out as 3/24 turns (1:8) or a 1:64... but after measuring with the NanoVNA I ended up removing 3 turns. I never even gave it a second thought it would have turned out as a 1:49.... Ha!
Anyways, Happy Holidays to all!
73, John W5EGA
|
Re: NanoVNA Function-Oriented Cheat Sheet
This video by Alan on the NanoVNA is a great intro. It gets a little technical for the uninitiated but definitely worth the time of watching it several times.
|
Jim,
Do you want to measure the impedance looking into the end fed wire itself?
A 67 ft long wire from 12 inches above ground straight to a tree at about a 70 degree angle comes in about 3700 to 3900 ohms shunted by about 8 pF at 7 MHz. Fed against an 8 ft ground rod.
I use a 1:49 transformer here (2 turn primary / 14 turn secondary). BTW 3 turns to 21 turns is also 1:49 not 1:64. As mentioned below by John, the Nanovna works fine at the low impedances.
To measure the wire directly I had to use a bridge that can measure high impedances. The Nanovna doesn't have the range and accuracy even for amateur radio. I use a General Radio GR-821. I used an other method as well with good agreement.
73, Pete
|
Barry Leonard KN4JRF
Alberto I2PHD
Martin Rigby