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Dave NU8A,

Thanks for taking the time to write your post. Your explanation was concise and well done.

Roger

Hello, can someone send me fm9688 chip? I know it can ordered from china, but there is new year season...Maybe from europe etc..pay via paypal--73 oh2lir

Dave, NU8A, and Jim Lux, thanks for filling in where I am unable. I do
detect a very slight difference connecting both conductors vs. measuring
only a single conductor, but your explanation makes it clear why. BTW:
The impedance of my lines on the toroids is between 80 and 100 ohms.
Fortunately, I have a good supply of carbon resistors to 'experiment' in
that respect. The line impedance is lower with the Teflon coated
conductor than with the DavisRF 'antenna' wire,likely due to closer
conductor spacing.

Again, thank you both for your inputs. Life should be a continuous
learning process! These NANO groups are great in that respect.

Dave - W?LEV

--
*Dave - W?LEV*
*Just Let Darwin Work*

The DM loss is primarily due to mismatch loss between the 50-ohm source impedance and impedance transformation caused by the bifilar pair behaving as a transmission line. The bifilar pair used here probably has a transmission line characteristic impedance of something around 100-120 ohms. If you take the bifilar pair by itself without any ferrite, and connect it between NanoVNA the ports, the DM loss measurement should be nearly the same as measurements made with the ferrite. What you see is impedance mismatch loss.

Here's the reason the ferrite has negligible effect with a differential signal. For all practical purposes, the magnetic fields around each wire in the bifilar pair are equal and opposite because the current in each wire is equal and opposite in differential mode. This makes the magnetic fields cancel and there's nothing left to interact with the ferrite.

So why does the mismatch loss go up with frequency? Because as the frequency goes up, the length of the bifilar pair as a transmission line increases in terms of wavelength. As this happens, the bifilar pair progressively transforms the load impedance seen at the source. As it moves away from 50 ohms, the mismatch loss increases. Maximum impedance transformation (and therefore maximum mismatch loss) happens at the frequency where the bifilar pair is a quarter wavelength long. (Making a few guesses about the length and characteristics of the bifilar pair, I estimate the max mismatch loss happens around 70 MHz with an impedance seen at the source of about 290 ohms.) If the frequency is raised further, the mismatch loss starts going down as the transformed impedance circles back to 50 ohms! Mismatch loss would be lowest at the frequency where the bifilar pair was now a half wavelength and the NanoVNA source port would see 50 ohms. (Of course there's no intention of using these particular chokes at VHF frequencies, this is just a way of explaining what's happening with the measurement.)

Dave NU8A

P.S. Purists may want to discuss parasitic reactances, incomplete field cancellation, and transmission line loss, but those effects will not significantly change the primary cause of the measured DM loss at HF frequencies with these chokes.

Using VSWR or Return loss is a practical idea to avoid the dynamic range
issue. Connect a 50 load to both the antenna port and the opposite input.
Connect the NanoVNA to the input port of the duplexer with the NanoVNA set
to S11 with either both or either VSWR or Return loss.the VSWR or Return
loss will increase at the point of the resonance or notch. I use this
method more than the through method. Of course once tuned you can use the
through method to determine the loss at the pass frequency.

I was also thinking about using a low noise broadband amplifier as stated
by W8LM.


*Clyde K. Spencer*



On Thu, Feb 11, 2021 at 11:13 AM Larry Macionski via groups.io <am_fm_radio=
[email protected]> wrote:

55 years as a ham, and years ago, hams made due with what they had and all
they had to tune duplexers was it's transmitter and receiver, a step
attenuator, another 2way radio, Dummy loads and a good VOM. There is a
procedure to do it like hat in an old ARRL Repeater Handbook Circa 1980.

Last January I tuned a old pair of WACO duplexers. with my NanoVNA. All
fine since. Since you have no experience... CHECK the duplexers 1st before
you start screwing around. READ up on everything on repeaters. Go to this
site and download the white paper on "ANTENNA DUPLEXERS".. Print it and
read it twice.



EMR is one of the oldest, most trusted in the business.. The Founder was a
ham and knew his stuff..

A setup to check --NOTE CHECK--- a duplexer.. #1. carefully calibrate
NanoVNA for 3-4 megs around the frequencies of interest. Rough pictorial
but you should get the drift of how to connect.

------------------ ch0
NanoVNA ch1-------------------------
|
|

------------------CAN-------CAN------CAN--------------- |

CAN CAN CAN | |

CAN CAN CAN | |

+-----------

|

|
50 OHM DUMMY LOAD
------------------CAN-------CAN------CAN---------------

CAN CAN CAN

CAN CAN CAN

Set your marker frequencies for repeater input and output frequencies
set display to make 2-3 passes 101 points X3..... as the plot bottoms out,
at -50- -60 dB, the curve will get ragged there. You want the marker to be
in the middle of the ragged area. I have not tried it yet, but I did buy a
$5-10 20dB 0-2Ghz broad band amplifier, to install in the CH0 line to see
if I can "raise" the plot to more accurately adjust the notch. Think of
CH0 as a transmitter and CH1 as a receiver.
I also used this setup to measure SWR at inputs.
Swapping CH0 with the dummy load, will test both sides of the duplexer...

I used VNA saver as you can increase the number of points on a plot to
X8.. all thought the sweep is slower. You can save your plots to a file or
print them out. more practical than the NanoVNA alone.

Larry W8LM

I found 2 of my plots,,done with a NanoVNA 144.76 -145.27

55 years as a ham, and years ago, hams made due with what they had and all they had to tune duplexers was it's transmitter and receiver, a step attenuator, another 2way radio, Dummy loads and a good VOM. There is a procedure to do it like hat in an old ARRL Repeater Handbook Circa 1980.

Last January I tuned a old pair of WACO duplexers. with my NanoVNA. All fine since. Since you have no experience... CHECK the duplexers 1st before you start screwing around. READ up on everything on repeaters. Go to this site and download the white paper on "ANTENNA DUPLEXERS".. Print it and read it twice.



EMR is one of the oldest, most trusted in the business.. The Founder was a ham and knew his stuff..

A setup to check --NOTE CHECK--- a duplexer.. #1. carefully calibrate NanoVNA for 3-4 megs around the frequencies of interest. Rough pictorial but you should get the drift of how to connect.

------------------ ch0 NanoVNA ch1-------------------------
| |
------------------CAN-------CAN------CAN--------------- |
CAN CAN CAN | |
CAN CAN CAN | |
+-----------
|
|
50 OHM DUMMY LOAD ------------------CAN-------CAN------CAN---------------
CAN CAN CAN
CAN CAN CAN

Set your marker frequencies for repeater input and output frequencies set display to make 2-3 passes 101 points X3..... as the plot bottoms out, at -50- -60 dB, the curve will get ragged there. You want the marker to be in the middle of the ragged area. I have not tried it yet, but I did buy a $5-10 20dB 0-2Ghz broad band amplifier, to install in the CH0 line to see if I can "raise" the plot to more accurately adjust the notch. Think of CH0 as a transmitter and CH1 as a receiver.
I also used this setup to measure SWR at inputs.
Swapping CH0 with the dummy load, will test both sides of the duplexer...

I used VNA saver as you can increase the number of points on a plot to X8.. all thought the sweep is slower. You can save your plots to a file or print them out. more practical than the NanoVNA alone.

Larry W8LM

OK, I got my analyzer few months ago and it is abut time for me to start using it.
My fist victim is going to be my Beverage " (sitting) on the fence setup".

I am NOT looking for accurate measurements , with precision of 5 decimal points , just get some idea how the wire behaves.

So - for starters - it is fed with very short length ( ~ 3 meters ) 450 Ohms "window line " .
How critical is it to "convert " such balanced feed to analyzer coax input?

Since the feed line is so short and ONE end of Beverage is GROUNDED - does it make much difference in measurements?
Cheers

73 Vaclav AA7EJ

John. Great idea.
I will try with my smart phone.
I am also going to try and do a screen p

In July 2020 I measured several chokes for an article in a magazine.

Compared two 240-31-cores. One with RG58, tight windings, and one with RG174, loose windings.
Of course, not one 31 core is equal to the other, but it gives a nice comparison. The core with RG58 is in use in my station for 3.5MHz - 10MHz. The RG174 (loosely wound) core was measured out of curiousity.

Draw your own conclusions.

Measurements were made with a nanoVNA H3.2 and nanoSAVER v0.1.2


To Hugen: thanks for bringing this nice device to market
To Rune Broberg: thank you for this marvellous piece of software.

73,

Arie PA3A


Op 11-2-2021 om 02:28 schreef Jim Lux:

On 2/10/21 5:15 PM, Mel Farrer via groups.io wrote:

YOU missed the fact that the difference in diameter from wire to coax shield will make a difference in the inductance value........................
Mel, K6KBE

bifilar windings are essentially twisted pair. The two conductors are separated by the insulation thickness, which is "small".? So the mutual coupling is "large"

On Wednesday, February 10, 2021, 04:20:20 PM PST, Jim Lux <jim@...> wrote:
On 2/10/21 9:05 AM, David Eckhardt wrote:

? Thank you for the great summary and information about measure CMC CM
attenuation. I have a couple of follow up questions for you and/or the
group, if I may. I notice the process is for bifilar chokes. And, it looks
like you only connect one wire of the bifilar turns to the VNA. You also
said you can connect both wires if you short both ends. I am still trying
to make sense of shorting both wires and why their wouldn't be a difference
in CM impedance compared to only connecting one wire. To me, it would seem
that connecting both ends together would create a parallel path and would
not be a true measurement of impedance (i.e. due to wires in parallel,
similar to two resistors in parallel). But, I know we are dealing RF and
ferrite toroids ... my intuition can't make that jump, yet.


*? I have actually tried one vs. both wires in parallel with the VNA in
measuring CM attenuation..? There is a very minor difference.? The largest
practical effect is to reduce resistance (not so much the ±jX portion). *

*? ? ? ? ? ? Considering? each wire of the bifilar pair contributes equal
inductance by itself, so the total connected in parallel will be half that
of each wire alone.? This ignores mutual coupling.? A 3 dB difference in
30 dB of total *

the mutual L of two parallel conductors is very close to the inductance
of a single conductor. There will be essentially no reduction in the L
from paralleling.

(this is why flat strap has lower AC resistance, but very close to the
same inductance, as a round wire with the same cross section)

It would have been much more fun if you let him find that out for himself ;)

YOU missed the fact that the difference in diameter from wire to coax shield will make a difference in the inductance value........................
Mel, K6KBE

On 2/10/21 9:20 AM, Reinier Gerritsen wrote:

Op 10-2-2021 om 17:15 schreef Jim Lux:

On 2/10/21 7:36 AM, mender5@... wrote:

I made some small changes of my Nanovna-H.
Is there a way to test s11 and s21 dynamic range?

S21 - start putting attenuators in and seeing where it bottoms out (or where the displayed attenuation change doesn't match the actual attenuation change)

S11 - calibrated mismatches - attenuator into an open or short. If you put a 20 dB pad on the Tx port, can you see the difference between short, open, and load?? (20dB pad is -40dB S11, 20 dB going out, 20dB coming back from the reflection).


A couple decent step attenutors (one in 10dB steps, the other in 1 dB steps) makes this easy.? But a handful of fixed attenuators can also do it, just more time consuming as you swap them around.


Watch out for leakage from cables etc as you get to higher isolations. 80 dB is hard. >120dB is really hard.

I would do it in a different way. Calibrate the analyzer. Terminate port 2 in 50 Ohm. The noise floor is the lowest level you can measure. To get the dynamic range you would need to know the maximum signal that can be applied. Therefore you would need an RF amplifier (input to port 1). Do not overload port 2, but to find the maximum usuable signal, you must find the level where it is no longer linear. You can find this level bij adding a know attenuator in series with the amplifier output. S21 should follow the attenuation.
S11 dynamic range: calibrate the VNA and do the 50 Ohm load as the last one. Leave it connected. Apply the calibration. Make sure you tell the analyzer (or the PC software) that the load is a perfect load. Now the displayed value of s11 is the dynamic range since it sees a perfect load, perfect in the sense that it is exactly the same as the reference.
For noise floor, take the peak values and add a few dB for safety margin. For S11 a dynamic range of 30 to 40 dB is enough for all practical applications.
All values are frequency dependent.

Note that a 20 dB attenuator does *not* mean a 40 dB return loss. Most likely it is less in practice if the input is not exactly 50 Ohm (or better, exactly the same as your reference)

True, it depends on the two impedances and the design of the attenuator. But into a short or open, if the VNA is 50 ohms, and the attenuator is 50 ohms, the difference will be "small"

On 2/10/21 9:05 AM, David Eckhardt wrote:

Thank you for the great summary and information about measure CMC CM
attenuation. I have a couple of follow up questions for you and/or the
group, if I may. I notice the process is for bifilar chokes. And, it looks
like you only connect one wire of the bifilar turns to the VNA. You also
said you can connect both wires if you short both ends. I am still trying
to make sense of shorting both wires and why their wouldn't be a difference
in CM impedance compared to only connecting one wire. To me, it would seem
that connecting both ends together would create a parallel path and would
not be a true measurement of impedance (i.e. due to wires in parallel,
similar to two resistors in parallel). But, I know we are dealing RF and
ferrite toroids ... my intuition can't make that jump, yet.


* I have actually tried one vs. both wires in parallel with the VNA in
measuring CM attenuation.. There is a very minor difference. The largest
practical effect is to reduce resistance (not so much the ±jX portion). *

* Considering each wire of the bifilar pair contributes equal
inductance by itself, so the total connected in parallel will be half that
of each wire alone. This ignores mutual coupling. A 3 dB difference in
30 dB of total *

the mutual L of two parallel conductors is very close to the inductance of a single conductor. There will be essentially no reduction in the L from paralleling.

(this is why flat strap has lower AC resistance, but very close to the same inductance, as a round wire with the same cross section)

I did an S21 test on my NanoVNA-H4 using precision SMA attenuators. This is what I got for 70 dB, 80 dB and 86 dB. You can get 80 dB out to about 200 MHz.

Roger

There was a recent thread in the TinySA group in regards to "resistive vs inductive" RF taps, not sure if that's what you are referring to.
/g/tinysa/topic/79601195

On Wed, Feb 10, 2021 at 01:35 AM, Peter Ivanooff wrote:

Halloooo.... miro - Your answers are nagging. Only bla, bla, bla.

You are right! I just assumed that you are genuinely interested in this subjects, but as many others using nanoVNA not formally educated in this "branch of science", so I tried to word it in a way that even a beginner can understand.

Now I see that I have made mistake, you do have "knowledge", even have a diagram that shows correct terminology, but are just sloppy with terminology and plain rude dude.

Should have said "check your question/statement as they make no sense. Once you do it all the rest will get addressed on it's own".

Obviously my bad!

Won't even dignify your other comments that have no place in this group.

Joao CU3AA what is the duplexer model you want to adjust?

This video also helped me to make the separate adjustment of each of the TPRD-1554.