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Failed to connect to MySQL: (1203) User howardkn already has more than 'max_user_connections' active connectionsPath: ...!weretis.net!feeder9.news.weretis.net!news.quux.org!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: john larkin Newsgroups: sci.electronics.design Subject: Re: Binocular choke extras Date: Thu, 20 Mar 2025 16:24:26 -0700 Organization: A noiseless patient Spider Lines: 76 Message-ID: References: <1r9gp9h.1k6o87n8sg91cN%liz@poppyrecords.invalid.invalid> <1r9hgjn.1ngpfg1zut24qN%liz@poppyrecords.invalid.invalid> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Injection-Date: Fri, 21 Mar 2025 00:18:48 +0100 (CET) Injection-Info: dont-email.me; posting-host="6dfee8a4b91ce726a49481b76b053813"; logging-data="286609"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+9fE5YLYKwvTKADP3JPZI1" User-Agent: ForteAgent/8.00.32.1272 Cancel-Lock: sha1:r63ZvYr9qYKhcRNqSL8paIQI52M= Bytes: 4503 On Fri, 21 Mar 2025 00:08:53 +0100, Jeroen Belleman wrote: >On 3/20/25 16:43, john larkin wrote: >> On Thu, 20 Mar 2025 10:49:08 -0400, Joe Gwinn >> wrote: >> >>> On Thu, 20 Mar 2025 07:30:58 +0000, liz@poppyrecords.invalid.invalid >>> (Liz Tuddenham) wrote: >>> >>>> Jeroen Belleman wrote: >>>> >>>>> On 3/19/25 22:40, Liz Tuddenham wrote: >>>>>> I've just taken delivery of a couple of ferrite 'binocular' choke cores; >>>>>> each one came with two thinwalled metal tubes and some bits of printed >>>>>> circuit board. The tubes appear to go through the holes in the choke >>>>>> and the holes in the boards fit over the ends of the tubes, with copper >>>>>> areas that could possibly be soldered to them. >>>>>> >>>>>> Does anyone know what purpose these serve? >>>>>> >>>>>> >>>>> >>>>> This sounds very much like the transformers used in wideband RF >>>>> power amplifiers. See for example Helge Granberg's application >>>>> note 762. The tubes with a piece of circuit board form the single- >>>>> turn low impedance winding, and a number of turns of insulated >>>>> copper wire going through the tubes form the high-impedance >>>>> winding. This makes for a good coupling factor and consequently >>>>> good wideband operation. >>>> >>>> That's the sort of thing I suspected. Each square pad surrounding the >>>> end of a tube is individually isolated but they could easily be joined >>>> to make a loop circuit with some wire straps. >>>> >>>> I intend using this as a 1:1 balun and was worried that the conventional >>>> way of twisting the primary and secondary conductors together before >>>> threading them through the core would create a capacitive imbalance. If >>>> I use the tubes as a 1-turn secondary and thread the inner of the feed >>>> co-ax through them, this will give much lower capacitance imbalance. >>> >>> This also sounds like it could be a transmission-line transformer; >>> these are very wideband. The ferrite cores serve as RF chokes, >>> ensuring the shield and center currents are exactly equal and >>> opposite. It is _not_ an ordinary RF transformer, despite the name. >>> >>> "Transmission Line Transformers", Fourth Edition, Jerry Sevick, W2FMI, >>> 2001, 289 pages, ISBN 1-884932-18-5, TK6565.T7 S48 2001, >>> 621.384'11--dc21. >>> >>> Joe >> >> I have the Sevick book but it's not very useful. >> >> We make super wideband tline transformers from micro-coax and pot >> cores. >> >> https://www.dropbox.com/scl/fi/32s2rfcu4q4iq6l6v1eb4/Pot_Core_TXline.JPG?rlkey=6k7xusurck0jf1ky9n6ja2ebz&raw=1 >> >> https://www.dropbox.com/scl/fi/adcocf1rb7lnanj7zo9xp/TX_1.jpg?rlkey=m7prsxj94fa57ynqoep0ydgnl&raw=1 >> >> Or toroids, which are harder to make. >> >> https://www.dropbox.com/scl/fi/xuqjzt3h1oq7uexwiu6c8/T750_1.JPG?rlkey=si165mntuu0h40zgsbi0qzxj7&raw=1 >> >> > >Those are 1:1 baluns. It's not too hard to get stupendous bandwidths >with those. Six decades of frequency should be quite easy. It gets >harder when you want different impedances at the ends. > >Jeroen Belleman I call them transformers. We use them to isolate pulse generator outputs, and sometimes to get a voltage step-up.