Finding out usable frequency of 9:1 balun with NanoVNA? - Page 1
Forum section: electronics / rf-microwave

author: vinlove
author_rank: Frequent Contributor
timestamp: February 07, 2023, 10:27:57 pm
content: 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?

author: vk6zgo
author_rank: Super Contributor
timestamp: February 08, 2023, 12:29:48 am
content: Quote from: vinlove on February 07, 2023, 10:27:57 pmRemember 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.

author: fourfathom
author_rank: Super Contributor
timestamp: February 08, 2023, 12:40:48 am
content: 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.

author: vinlove
author_rank: Frequent Contributor
timestamp: February 08, 2023, 06:22:49 pm
content: Also found this video very helpful.

author: Axk
author_rank: Regular Contributor
timestamp: March 26, 2023, 04:15:03 pm
content: 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.

author: iMo
author_rank: Super Contributor
timestamp: March 26, 2023, 04:50:46 pm
content: 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?

author: Axk
author_rank: Regular Contributor
timestamp: March 26, 2023, 05:17:41 pm
content: 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.

author: A.Z.
author_rank: Super Contributor
timestamp: March 27, 2023, 06:02:50 am
content: the nooelec 9:1 v1 shown in the image uses this transformerhttps://www.coilcraft.com/en-us/products/transformers/wideband-rf-transformers/smt/wbc/wbc9-1l/for schematic and infos see the downloads section herehttps://www.nooelec.com/store/balun-one-nine.htmlby the way the above is true if the balun is from nooelec, if it's a chinese clone, then all bets are off