what balun to use - Page 1
Forum section: electronics / rf-microwave

author: p.larner
author_rank: Frequent Contributor
timestamp: December 09, 2023, 10:02:56 am
content: my feeder is 450 ohm windowline,what sort of balun do i need to go to a 50 ohm atu input.9-1?.

author: A.Z.
author_rank: Super Contributor
timestamp: December 09, 2023, 10:13:02 am
content: 1:1 those 450 Ohm are the CHARACTERISTIC impedance of the feeder, NOT the impedance seen at its end, and "50 Ohm ATU" is total nonsense, go on refusing to LEARN

author: Andy Chee
author_rank: Super Contributor
timestamp: December 09, 2023, 10:25:36 am
content: use a 1:1 balunhttps://www.dj0ip.de/balun-stuff/tuner-baluns/As commented above, do not confuse transmission line characteristic impedance with antenna impedance, they are two separate concepts.

author: A.Z.
author_rank: Super Contributor
timestamp: December 09, 2023, 10:44:49 am
content: https://en.m.wikipedia.org/wiki/Characteristic_impedanceyou want THIS onehttps://www.dj0ip.de/rf-cmc-chokes/different-kinds-of-chokes/d2-guanella-choke/

author: A.Z.
author_rank: Super Contributor
timestamp: December 09, 2023, 11:40:31 am
content: Quote from: A.Z. on December 09, 2023, 10:44:49 amand then, considering your limitations, you may also have a look herehttps://owenduffy.net/transmissionline/stcm/index.htmhttps://www.m0mcx.co.uk/how-to-use-dual-coax-feeders-as-ladder-line/https://www.southslope.net/~kb0sk/antenna.htmlhttps://archive.org/details/spencerpdfbut then, I suspect I wasted my time once more

author: A.Z.
author_rank: Super Contributor
timestamp: December 09, 2023, 01:29:52 pm
content: the thing you MUST understand is HOW a BalUn (a current one, not a voltage one... we may fathom it later on) works, and WHAT and HOW/WHY it does it, let ASIDE impedance transformation, start FLAT, and if you'll get a grip on that IF you use your brain ...

author: vk4ffab
author_rank: Frequent Contributor
timestamp: December 09, 2023, 09:47:29 pm
content: Quote from: p.larner on December 09, 2023, 10:02:56 amAs per your other thread, you need a 1:1 at the dipole feed point and a 4:1 at the tuner. The 1:1 keeps the legs of the antenna balanced and isolates the window line, the 4:1 just changes the impedance extremes into something the atu-100 can handle and transforms the balanced line into an unbalanced tuner.Antenna system wise, this is then no prune and the losses will be acceptable. You do not need to measure 50 ohms at the tuner, in such a situation.

author: p.larner
author_rank: Frequent Contributor
timestamp: December 13, 2023, 04:58:30 am
content: can i put an ugly choke/balun at the feedpoint then connect that to windowline,then a 4-1 balun at the tuner end then?,heres the polar plot of my antenna windowline connected to my vna,no balun or coke etc,i already have an ugly balun made from rg-213 on an 6 inch pipe with 20 turns on it,thats why i ask.

author: p.larner
author_rank: Frequent Contributor
timestamp: December 13, 2023, 06:02:16 am
content: i am told a 1-1 balun should be bifilliar but have found this,whats best 3 wire type or 2?,just seems confusing to me one lot of folks saying it needs to be 2 wire.

author: Andy Chee
author_rank: Super Contributor
timestamp: December 13, 2023, 09:57:39 am
content: I’m inclined to believe two wire. Can you post a link to the person saying three wire?This balun is constructed with bifilar windings:https://owenduffy.net/blog/?p=687

author: p.larner
author_rank: Frequent Contributor
timestamp: December 13, 2023, 10:59:05 am
content: was this in the pic,just not sure what number of turns on a ft-240 43 core to wind

author: Andy Chee
author_rank: Super Contributor
timestamp: December 13, 2023, 11:55:09 am
content: Ok, that three wire 1:1 balun in your image is a voltage balun, which is incorrect for your purpose.For your purpose, you need a 1:1 current balun.https://vk6ysf.com/balun_guanella_current_1-1.htmFor 80m, you will probably need about 16-17 turns, just fit as many as you can in one layer without overlapping layers.

author: A.Z.
author_rank: Super Contributor
timestamp: December 13, 2023, 04:28:08 pm
content: Quote from: Andy Chee on December 13, 2023, 11:55:09 amthe guanella above isn't bad, but I'd rather suggest this onehttps://www.dj0ip.de/rf-cmc-chokes/different-kinds-of-chokes/d2-guanella-choke/and then, for the 4:1, I'd suggest this other onehttps://www.m0pzt.com/blog/4to1-current-balun/both are easy to wind/build and they can all use the same FT240-43 toroids, three of them will suffice for the task, then it remains to see if he really needs a 4:1, see, if the impedance goes too low, the ATU he's using won't be able to match it

author: A.Z.
author_rank: Super Contributor
timestamp: December 13, 2023, 04:43:50 pm
content: Quote from: p.larner on December 13, 2023, 04:58:30 amA so called "ugly balun" will ONLY be effective on a limited frequency range, it may be ok for well balanced SINGLE BAND antennas, but if used on multiband antennas or unbalanced antennas, not only it will have little effect, but it may even make things WORSE !

author: p.larner
author_rank: Frequent Contributor
timestamp: December 13, 2023, 06:18:51 pm
content: well ive made this(see pic),i am told i need 2 cores for the 4-1 transfo,guess i may as well try it,am i best fitting it at the rig side of the atu?

author: A.Z.
author_rank: Super Contributor
timestamp: December 13, 2023, 08:04:58 pm
content: GFYBOH

author: Andy Chee
author_rank: Super Contributor
timestamp: December 13, 2023, 08:14:14 pm
content: Quote from: p.larner on December 13, 2023, 06:18:51 pmConnect your balun(s) between ATU and antenna feedline. NOT rig side!

author: p.larner
author_rank: Frequent Contributor
timestamp: December 13, 2023, 10:42:38 pm
content: Paul M3VUV10:40pm #364well i am trying this,firstly the windowline goes into the choke as in the first pic,then goes to a 4-1 balun made with 2x 240-43 torroids then to the tuning elements in the tuner,pic 2,should that be ok?,all 3 cores are 43 material.

author: p.larner
author_rank: Frequent Contributor
timestamp: December 18, 2023, 09:47:50 am
content: ive wound the ballun linked by andy chee,but used thin coax,is that ok,i think its rg-174.

author: A.Z.
author_rank: Super Contributor
timestamp: December 18, 2023, 03:05:52 pm
content: Quote from: p.larner on December 18, 2023, 09:47:50 amand, the question is ?A suggestion, considered the sub-optimal setup of your "so-called" doublet antenna and the problems you keep facing, consider the idea of setting up a terminated antenna, like for example a T2FD or a terminated horizontal loop antenna, feeding it directly with coaxial cable through a 16:1 BalUn followed by a good Guanella choke, I know you'll keep ignoring the suggestion as you kept ignoring the requests to sweep your antenna using the VNA, but given that you're still wandering in the dark I thought it was the case to refrain the suggestion, and in case you don't understand what a terminated loop is, just start herehttp://hflink.com/antenna/#BBTDROOFand scroll down, such an antenna will probably give you better results than your poor "doublet" and will still be "stealth" (note: scrolling further down the page you'll also find the design for the 16:1 BalUn to use with those terminated antennas)btw, you remain the same, you are not pushing yourself "up"; the idea remains the same, up to you changing if you can and want, otherwise...maybe someone will notice the way you behave, and good luck then.

author: p.larner
author_rank: Frequent Contributor
timestamp: December 19, 2023, 09:00:34 am
content: i removed the 4-1 balun but kept the 1-1,also made the feeder about 3ft longer,it seems ok now 73.

author: A.Z.
author_rank: Super Contributor
timestamp: December 19, 2023, 01:00:50 pm
content: Quote from: p.larner on December 19, 2023, 09:00:34 amwell, finally you took a good step, now... plug the vna after the 1:1 and sweep the antenna to obtain the impedance curve, at that point, having such infos it will be possible to find out if an impedance transformer may help, in such a case the connection will be antenna (balanced line), N:1 (voltage) transformer, 1:1 (current) balun/choke, coax to shack, ATU, TRXThe idea is to reduce the impedance mismatch using the transformer and balance currents with the balun/choke so that there will be less losses along the coax and little CMC, at that point the ATU will correct the mismatch and make the RTX happy; if you want you may add two further chokes, one at the ATU antenna input and a second one between the ATU and the RTX