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Moderated Re: Another off-topic about Smith chart

 

Actually, the Smith chart is "normalized" to whatever the impedance that you are working with, usually 50 but could be 75 or 450 if open wire feed line.The operation to compute is as John described, Multiply every number on the chart by the impedance you are normalized to.
Gary
Moderated Re: Another off-topic about Smith chart

 

Hi,

The scale is neither linear nor logarithmic, and I¡¯m not sure what it is.

Luckily it does not matter if you just want to use the smith chart.

Generally for radio work the centre is defined as 50 ohm; that is a resistance of 50 ohms would be plotted at the centre of the chart, a resistance of 100 ohms would be plotted at the 2.0 position.

The rule is divide whatever the impedance is by 50 and plot the new figure on the chart. Conversely to get a value from the chart take the reading from the chart and multiply by 50 to get the actual values.

It seems complicated but a bit of practice will make it easier.

Good luck

73
John
M0JBA

On 25 Mar 2020, at 15:05, vaclav_sal via Groups.Io <vaclav_sal@...> wrote:

An off - topic question to any math wiz knowledgeable about Smith chart.
There are oodles of stuff about Smith chart, but I have not be able to find
WHAT is the actual scale of the coordinates.
For example
real axis ( R +j0) goes from "zero" (left) to center of the chart - MOST of the time
designated as "one" .
Therefore - what is the scale between 0 and 1 - linear or log?
( No need to discuss log(0))
It PROBABLY makes no difference, but IMHO log scale would "loose" some visual
precision.
Please, no sermons / references about what is Smith chart , how to use it etc.
Sorry to post here , but I have limited choice.



Moderated Re: Another off-topic about Smith chart

 

Not a math wiz here but one of the best ways I learned about the chart back in college was to see the mathematical calculations (and thus derivations) for the actual circles. The smith chart has unique scales based on those equations which is why they are different from things you may be used to seeing. Have a look at this simplified (but well written description) of the derivation of the chart and see if that helps you visualize why the scales are so unique and why they look the way they do. I am still in awe at the genius involved almost a century ago for someone to come up with the concept. True brain power & genius.



Gedas, W8BYA EN70

Gallery at
Light travels faster than sound....
This is why some people appear bright until you hear them speak.

On 3/25/2020 11:05 AM, vaclav_sal via Groups.Io wrote:
An off - topic question to any math wiz knowledgeable about Smith chart.
There are oodles of stuff about Smith chart, but I have not be able to find
WHAT is the actual scale of the coordinates.
For example
real axis ( R +j0) goes from "zero" (left) to center of the chart - MOST of the time
designated as "one" .
Therefore - what is the scale between 0 and 1 - linear or log?
( No need to discuss log(0))
It PROBABLY makes no difference, but IMHO log scale would "loose" some visual
precision.
Please, no sermons / references about what is Smith chart , how to use it etc.
Sorry to post here , but I have limited choice.
Moderated Another off-topic about Smith chart

vaclav_sal
 

An off - topic question to any math wiz knowledgeable about Smith chart.
There are oodles of stuff about Smith chart, but I have not be able to find
WHAT is the actual scale of the coordinates.
For example
real axis ( R +j0) goes from "zero" (left) to center of the chart - MOST of the time
designated as "one" .
Therefore - what is the scale between 0 and 1 - linear or log?
( No need to discuss log(0))
It PROBABLY makes no difference, but IMHO log scale would "loose" some visual
precision.
Please, no sermons / references about what is Smith chart , how to use it etc.
Sorry to post here , but I have limited choice.
Re: Check impedance of an unknown coaxial cable

 

Thanks a ton guys! have some 50ohm for dummy loads I planned to build, will use and report.
Re: ? nanovna-saver best fw ? #nanovna-saver

 

Hi Larry,

Thanks.

I have one from the first batch, I am used to upgrade.

And it's so easy to go into dfuse mode...
Re: ? nanovna-saver best fw ? #nanovna-saver

 

Newer FW versions add functionality and/or correct errors.
Any FW version from the beginning of 2020 will do and they are easy to flash into the device.

On Tuesday, March 24, 2020, 2:26:17 p.m. GMT-4, CT2FZI <ct2fzi@...> wrote:

Thanks, but sorry I did not get if you answered my question: best fw for nanovna-saver

Cheers and thanks
Re: ? nanovna-saver best fw ? #nanovna-saver

 

Thanks, but sorry I did not get if you answered my question: best fw for nanovna-saver

Cheers and thanks
Re: V2 Design #nanovna-v2

 

Thank you
it seems I am too late...

Chris

---
'Everything should be made as simple as possible, but not simpler.' -- Albert Einstein

Am 24.03.2020 um 11:23 schrieb CT2FZI:

Tindie out of stock - I have purchased their last unit :)
Re: V2 Design #nanovna-v2

 

On Tindie you can pay with Paypal. In my account I can use it for paying...

Chris

---
'Everything should be made as simple as possible, but not simpler.' -- Albert Einstein

Am 05.03.2020 um 21:27 schrieb Larry Rothman:

Hi Gabriel,
It would be great if you could find out from the seller/manufacturer is they would be willing to accept PayPal payments via email, the same way that Maggie King did for Hugen's devices.
I'd love to get one of these if that method is available.
Thanks,Larry

On Thursday, March 5, 2020, 10:39:22 a.m. GMT-5, Gabriel Tenma White <owowowowo123@...> wrote:
Here's the link to the taobao listing:
Although if you are outside China I would wait for the tindie listing; it's supposed to be awaiting approval now.
Re: ? nanovna-saver best fw ? #nanovna-saver

 

The nanovna saver is not currently being developed
because of the busy programmer.
Latest Version: 0.2.2.1 (Python 0.2.2)


The 2.8-inch core nanovna edy555 version 0.7.1-20200321,

while the Hugen version is 0.4.5-4.
beware, because here you can find the version of -H4 you need -H


Otherwise, check out the Wiki folder.
? nanovna-saver best fw ? #nanovna-saver

 

Hi everyone,

From all the firmware versions for the nanovna-H (original) what firmware do you recomend to take the most from the nanovna-saver?

Or, is the nanovna-saver agnostic to fw version?

Cheers and thanks
Re: Check impedance of an unknown coaxial cable

 

Howdy Pablo! This virus should has thrown the world into turmoil... I hope it turns out to be a minor virus, not as bad as the flu.
As far as coax for antenna for an H/T, I would assume around 145 MHz and/or 445 MHz for ham bands?

I use a good quality RG-6 for my scanners. This is of course adding in a 1.5:1 SWR but due to being used receive only, it's of little consequence.
I have 800 MHz trunking systems I monitor as well as low band VHF (45 MHz) and the coax I swept is pretty wide band and low loss. I have multiple scanners so I use a small CATV distribution amplifier. Each port is 7 db gain so it compensates for coax losses. I have under 20 meters going to a discone antenna. The amp does provide a bias-t function so i could use an LNA at the antenna....the one I have is 17 db gain but I don't need it. My scanners all have BNC antenna connectors so I use a BNC-F adapter and then about .7 meter pigtails of RG-6 from the amp to the receivers. It all appears to work well.
Food for thought or maybe excess information....

73 de Tim, K4SHF
Re: Analysing Input Impedance Matching Circuit for the NE602

 

Hi Roger,

Thanks for this, your results look very similar to mine, there is a slight difference in the frequency of the dips but I assume this is due to differences in the mix of the core material, winding pattern (causing a difference of capacitance between turns) and also stray capacitance and inductance on connecting wires.

The images below show my results of two back to back 1T to 8T impedance transformers using BN73-202 binocular cores with plastic insulated wires compared to yours (mine look just like the ones in the photo you attached, they are wound in exactly the same way). I have added your images next to my results for comparison, mine are the left ones and yours are the right ones.

I am pleased my results match so closely to yours - it is always helpful to be able to compare results.

Thanks for taking the time do do this.

S21 back to back transformer comparison.png
return loss back to back transformer comparison.png
VSWR back to back transformer comparison.png

Re: V2 Design #nanovna-v2

 

Tindie out of stock - I have purchased their last unit :)
Re: Analysing Input Impedance Matching Circuit for the NE602

 

Kerr,

I wound two 1T to 8T impedance transformers using BN73-202 binocular cores and insulated, solid, silver-plated wire-wrap wire. They were connected back to back and the 1T sides soldered to SMA connectors as shown below. NanoVNA Saver was used to make the measurements from 1 MHz. to 30 MHz (plots below). The worst case S21 loss was 5.9 dB at 30 MHz. (back-back) which is about 3 dB for one transformer. In the 40M band the S21 was -2.69 dB (back-back) or -1.35 dB for one transformer which is quite good. Return loss (S11) varied from 12 dB to 3.71 dB across the 30 MHz. test range.

There is enough room in the core holes to wind 2T to 16T but I have not done this yet.

1T to 8T BN73-202.png
S11 Return Loss.png
S11 VSWR.png
S21 Gain.png

Re: Check impedance of an unknown coaxial cable

 

Pablo you can also take a look at this video that is very detailed on how to determine the impedance and velocity factor of any unknow coax cable:
Re: Check impedance of an unknown coaxial cable

 

Saludos Pablo,

You could use the TDR function of the NanoVNA to check the impedance of an unknown coax cable by soldering a non-inductive variable resistor (value within the range of the suspected cable impedance) at the far end of the coax cable. Normally if you leave the end of the cable open circuit you will see a reflection due to the impedance mismatch. Vary the value of the variable resistor and once you see that the reflection is gone you know that the resistance that the variable resistor is set to is equivalent to the cable impedance. Just measure the resistance of the variable resistor with a DMM and you're good to go.

Hope that helps.
Alex
Re: Dang! I Dropped It..

 

Had exactly the same DANG here. Totally loose display and connector broken.

I was able to resolder the display onto the pcb. Took me 5 times of trying but I succeeded :-)

Give it a try.

73,

Arie Pa3a
Re: Check impedance of an unknown coaxial cable

d balfour
 

50 or 75¦¸, it shouldn't make a big difference unless you are wanting to push high power through it.
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