Finding out usable frequency of 9:1 balun with NanoVNA?

[vinlove]

I am getting used to using NanoVNA which arrived a few days ago.  I made many stupid mistakes in using it, and also asking many stupid questions, I feel I am getting to know it more day by day.   The RF Demo Kit for NanoVNA was great help too.

Anyhow, now I am thinking of ways of using NonoVNA to analyse a 9:1 HF balun that I bought a few year ago. It is found in the drawer, but it doesn't say anything on the freq. range it covers.  I recall it was definitely for HF bands.  But would it cover MW and LW too? And upto what frequency does it cover?
So to simple put, would it be possible to find out the lower and upper limit of the frequency the balun covers with NanoVNA?  If yes, then how would you do it?

[vk6zgo]

I am getting used to using NanoVNA which arrived a few days ago.  I made many stupid mistakes in using it, and also asking many stupid questions, I feel I am getting to know it more day by day.   The RF Demo Kit for NanoVNA was great help too.

Anyhow, now I am thinking of ways of using NonoVNA to analyse a 9:1 HF balun that I bought a few year ago. It is found in the drawer, but it doesn't say anything on the freq. range it covers.  I recall it was definitely for HF bands.  But would it cover MW and LW too? And upto what frequency does it cover?
So to simple put, would it be possible to find out the lower and upper limit of the frequency the balun covers with NanoVNA?  If yes, then how would you do it?

Remember that the impedance of the antenna on the High Z side of the balun does not remain the same at all frequencies, so if you, say, loaded that side with a high value resistor & tested it, you could end up with false expectations of the frequency range it would be useful for.

[fourfathom]

Put a 450 Ohm resistor (9 x 50) on the hi-Z side of the balun, and connect the other end to the VNA input port.  Measure the impedance (or SWR if you like) over the frequency range of concern.  This tells you most of what you need, except loss.  For loss, build a resistive 50 Ohm to 900 Ohm matching pad and put that on the Hi-Z side of the balun.  You can then to a two-port loss measurement over the range of interest.  Subtract the loss of the matching pad and you have your loss numbers.

[vinlove]

Also found this video very helpful.

[Axk]

Hello everyone!
I'm doing the same thing as the OP.
Measuring S11 at the balun (9:1 Noo Elec nockoff) with a 460R resistor across the high impedance side of the balun.

If the balun is good should I expect more or less resistive S11 from 1MHz to 25MHz?

Seeing (1+j5)R at 50KHz, 35R at 3.7Mhz and (20-j16)R at 25Mhz. The lowest SWR is about 1.5 at 4 MHz, 2.8 at 25Mhz.
S11 IS mostly resistive and in the 9:1 ratio with a 47R resistor on the high impedance side though.

[iMo]

A good 1:9 unun should show swr<1.5 from 3 to 30MHz when loaded with 450ohm none-inductive resistor. Doublecheck your winding's wiring and your nanovna calibration as well.. What is your toroid material like, btw?

[Axk]

It's not a DIY balun. I don't know what material is used.
The core is tiny.

I've measured the resistor separately and it doesn't show any noticeable inductance in the frequency range.

[A.Z.]

the nooelec 9:1 v1 shown in the image uses this transformer

https://www.coilcraft.com/en-us/products/transformers/wideband-rf-transformers/smt/wbc/wbc9-1l/

for schematic and infos see the downloads section here

https://www.nooelec.com/store/balun-one-nine.html

by the way the above is true if the balun is from nooelec, if it's a chinese clone, then all bets are off

[firewalker]

This is the results fro 3 to 30 MHz for one from Aliexpress. Is it acceptable?

Alexander.

[RFDx]

This is the results fro 3 to 30 MHz for one from Aliexpress. Is it acceptable?

With 450 Ohm termination? The flat return loss does rather suggest you have a (pretty good) 16:1 transformer. A Smith diagram would clear things up.

[firewalker]

Yes, with 450 Ohm non inductive load.

[joe8031]

Because there are unknown cores I will post specs (leaving out the brand name) for a known core used 9:1 to impedance match antenna.
The nanoVNA being very helpful, it is covered by members above. Some known details to compare to your no details China mystery core.
Something to compare to:

FT140-43, ID=.9", OD=1.4", RFI Range 25-300 MHz
the A(L)=1060 it is rated for 250 W PEP noting that temperature will change this.

Generally an end fed antenna Ferrite Toroid Core T140-43 for 1.0MHz to 60MHz.
Most of the lower band antennas are not spectacularly efficient. Some magnetic loops do well.

One website having useful material on baluns: https://vk6ysf.com/unun_9-1_v3.htm




 

[rf-fil]

Another way to test RF transformers is to connect two of them back-to-back, with the 50-ohm sides facing out, and then measuring them in "through" mode with a VNA. That tells you the loss and the frequency range. Actual loss and attenuation is half of what you're seeing with the VNA, obviously.

[RFDx]

Yes, with 450 Ohm non inductive load.

Transformer is fine, has a negligible reactive component but a rather odd transfer ratio.

[A.Z.]

Yes, with 450 Ohm non inductive load.

Transformer is fine, has a negligible reactive component but a rather odd transfer ratio.

if by "transfer ratio" you refer to the transformation ratio, then throw it away, a 9:1 must be a 9:1 not a something else: 1 get serious