using rg-58 for a balun - Page 1
Forum section: electronics / rf-microwave

author: p.larner
author_rank: Frequent Contributor
timestamp: November 21, 2023, 02:50:17 am
content: can i make a 1-1 balun like this using rg-58?and an ft-240-43 torroid?.

author: VK2AZT
author_rank: Newbie
timestamp: November 21, 2023, 06:44:47 am
content: If you wanted to make an UNUN, go for it. You would be running the risk of the RG-58 crushing in on itself as the bending radius of the coax would be too small. Eventually the centre conductor would short to the braid but this would take quite a long time so don't worry about it. By using the coax you would make a nice common mode choke (CMC). This may work with your new antenna. Try it and see. It doesn't take long to wind one of these things.Cheers.

author: A.Z.
author_rank: Super Contributor
timestamp: November 21, 2023, 06:44:54 am
content: yes

author: Andy Chee
author_rank: Super Contributor
timestamp: November 21, 2023, 08:42:01 am
content: Yes.The picture you posted is commonly known as Reisert winding, designed to keep the input and output separated in order to minimise capacitance.I use 12 windings of RG-58 (6 turns one side, 6 turns on the other) on a FT240-31 but #43 mix should be ok as well.

author: A.Z.
author_rank: Super Contributor
timestamp: November 21, 2023, 11:45:27 am
content: Quote from: Andy Chee on November 21, 2023, 08:42:01 amI found that 17 turns (8+1+8) on a #43 result in a pretty good choke/balun over the 3.5...30 MHz range, willing to use higher power, the RG58 may be replaced by RG142, otherwise. using the RG58 and an FT240-43 core, the balun will be good for about 200W

author: p.larner
author_rank: Frequent Contributor
timestamp: November 23, 2023, 06:24:15 am
content: i know it will work as a common mode choke but will it transfer/match 300 ohm windowline to 50 ohm coax,ie work as a balun?.

author: A.Z.
author_rank: Super Contributor
timestamp: November 23, 2023, 06:59:54 am
content: Quote from: p.larner on November 23, 2023, 06:24:15 amit will work as a BalUn, that is, it will BALANCE the currents so it will also avoid the insurgence of common mode currents; that said, 300 Ohm is the CHARACTERISTIC impedance of that window line, do you know what it means ?

author: Andy Chee
author_rank: Super Contributor
timestamp: November 23, 2023, 07:09:46 am
content: Quote from: p.larner on November 23, 2023, 06:24:15 amYes. Here's more info:https://www.dj0ip.de/balun-stuff/tuner-baluns/d-i-y-tuner-balun/

author: A.Z.
author_rank: Super Contributor
timestamp: November 23, 2023, 03:26:01 pm
content: Quote from: Andy Chee on November 23, 2023, 07:09:46 amAnd then... given that the OP seems to be quite confused about baluns, or probably doesn't understand what a BalUn does, I'd suggest him to read the followinghttps://www.dj0ip.de/balun-stuff/balun-overview/http://www.arrl.org/files/file/History/History%20of%20QST%20Volume%201%20-%20Technology/AntComp1-Lewallen(1).pdfand then, stop for a split second and think; common mode currents are raised due to current imbalance, a BalUn purpose is to balance currents, so asking if a current BalUn like the one posted will act as a choke, means that one will need to stop and document a bit better about BalUns, and the above links may be of some help imVHo; then... there would also be to talk about BalUns and impedance transformers, the two aren't necessarily the same, and to add a bit more, the characteristic impedance of a given transmission line (say a 450 Ohm ladder line) has nothing to do with the impedance seen at one end of some length of such a line, when the other end is connected to a load presenting a composite impedance, and this sounds like the OP needs to further document about such topics