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-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Gert Gremmen
Sent: Monday, January 13, 2020 7:04 AM
To: [email protected]
Subject: Re: [nanovna-users] How to find the right ferrite toroid for a receiving antenna balun?

What you are looking for is a minimum loss situation.

All ferrites are the same but for Al value (always freq dependent) and
hysteresis losses. Any low loss ferrite will do for your balun once the
optimum wire thickness and winding number is achieved.

Low loss characterization would be easiest when doing a simple 1:1
transformer as all impedances remain (the same) 50 Ohm.

Than just characterize at your frequency of interest, the transfer value
as a skalar (no need here for complex measurements)

Then make a 9:1 balun (arbitrary N windings) and use a 400 ohm serial
resistor (to make sure it is loaded by 450 Ohm) to the input of the
nanoVNA (400 +50(input nano) = 450) to verify you were looking for.
Alternately you can reverse the measurement by inputting into the "9"
side + 400 and loading the "1" side. (Losses shall essentially be the
same, if not, set up problem)

Then connect the "1"side of the balun to your receiver (without 400 Ohm)
and characterize the "9" side for SWR and having a 450 Ohm real input.

(you might characterize the 400 ohm resistor first (to be
non-inductive) so as to make sure it does not spoil the measurement, and
allowing you to measure the transfer losses created by the resistor)

Once you found best ferrite you may experiment with winding numbers (to
cope for the specific Al value of your ferrite) and optimize the
transfer to your receiver. Experiments may be bifilar winding, other
geometries of the ferrite, (though you will find a correlation between
ferrite volume and losses,so keep it small) and winding variations and
interconnections. The last parts are the fun in this hobby.

If you do a good job, your balun may function from 300-30000 kHz. It is
difficult to have more than 1:100 in frequency range for a non tuneable
balun, due to non-symmetries in windings and interconnects.

My 1 cents.....

Gert

On 13-1-2020 12:06, ptapon@... wrote:

Hello everyone,

A newbie set of questions.

On the net, you have as many opinion, way of measuring etc. as you have pages with the word ferrite in it.
Moreover, they are too few discussion to how to characterize a ferrite with a VNA. Bunch of stuff for common mode chokes and the like, but not a lot for baluns
Given we have now a wonderful set of tools, NanoVNA and nanoVNA Saver, I'd like to understand how to make the right choice.

I'm only interested in receiving antennas, therefore no power will go through, no heating concerns etc.
I'm, for now, interested in HF bands with, for now, a long wire.
I'm therefore aiming for a 9:1 balun.
I have a bunch of "no names" ferrites in my junk drawer, some from power supply, therefore likely good for KHz ranges and others from various sources.
As many of us, amateurs, I tend to use what I have handy, and not building, from a web page, the, say, Fair-rite type 43 with 9 turns of 26 AWG, without "fully" understanding what I am doing.

My main question:
What will be the characteristics to look for when comparing ferrites - and choosing the best one- for a 0-30Mhz 9:1 balun?

I have built an enclosure with dual sided PCB and SMB connectors (from another junk drawer :-) ) with a 50R resistor at the input SMB.
Calibration is done with the enclosure. I'm using the same wire I will likely use for the balun, between the input and either the ground or another SMB connected to S2.

I have already zillions of NanoVNA saver screen shots with various ferrites but I'm unable to find the right info to make a decision.
Will it be from the smith chart, SWR, Z, return loss, ??

Is there a way to find the right ferrite without winding a 9:1 balun each time.

When testing a 9:1 balun:
Do I need to load the "output" of the balun with a 450R resistor?
Do I need to connect the output (loaded or not) to the S2 ?
If yes, what will be the right info to look for?

Any help or pointer to the right docs will be helpful.
Thanks in advance

Jean

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