Trifilar 1:4 balun for diode ring mixer using binocular cores? - Page 1
Forum section: electronics / projects

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: November 15, 2015, 05:08:22 am
content: So I am trying to build an up converter for an RTL SDR. I have watched w2aews videos and pete julionas stuff on diode ring mixers. They all use toroids and they call confuse me because there is no theory explained when it comes to baluns, they just say cut wires this long wind together and wrap X times around a toroid.Well im broke and I have diodes and all kinds of good stuff but I dont have any toroid rings... I scrapped some binoculars out of an old sony black and white CCTV crt used in the modulator box. I dont know the material nor do I care.... I will buy proper materials when I can for now I just want to experiment.If I want to do this using binocular cores, Im guessing a pretwist 3 wires, 2 are half the length of the first and then I just pass those in a u shape around the binoculars center, and that is one turn. But how do I know how many turns lets just assume its broadband ferrite to 200mhz.... am I going about this all wrong?I also have ferrite bars from AM sticks but I have no idea how to make that work either.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: November 15, 2015, 05:13:45 am
content: Quote from: rwgast_lowlevellogicdesin on November 15, 2015, 05:08:22 amI'm not familiar with the circuit but assuming it's the standard arrangement with a diode balanced mixer, you pretwist all 3 wires and connect the end of one winding to the start of another winding. Another winding is not connected to either of the other two. All three windings are the same length.The number of turns isn't that critical as these are broadband transformers. Although it's bigger you should be able to use a ferrite rod from a transistor radio as the former - after all this is used for 1:1 baluns for 2-30 MHz as used at antenna feedpoints etc.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: November 15, 2015, 06:58:30 pm
content: Ya I could only get three turns of 30ga magnetic trifilar wire through the little binoculars I found. since im doing HF up conversion the transistor radio rods will work perfect. I guess im just not understanding how the number of windings is determined and what the transformers are actualy matching, impeadence between LO, IF, RF? Im just building a standard double balanced diode mixer.Secondly I have some 12c programmable DS1077s on hand can I use those for the LO they are adjustable up to 133mhz?https://www.sparkfun.com/datasheets/Components/SMD/DS1077.pdf]https://www.sparkfun.com/datasheets/Components/SMD/DS1077.pdf, I got them for dynamically clocking micros so there not a sign wave like other DDS's. Ive also added a 28.8mhz TCXO to my SDR dongle what happens if the dongle and the down converter use the same LO?

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: November 15, 2015, 07:55:35 pm
content: 10 turns on a ferrite rod should be OK for HF.

author: AF6LJ
author_rank: Unknown
timestamp: November 15, 2015, 08:20:25 pm
content: I don't think the ferrite rod from an AM radio is going to work.For one thing toroids are chosen for their self shielding properties.Get yourself a copy of any of mid 70s to late 80s ARRL handbooks or Experimental Methods in RF Design. The books can be had cheap enough and have a wealth of information on the subject. The core material Does matter and since you are up-converting HF the material must be usable from HF through your local oscillator frequency.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: November 15, 2015, 10:37:46 pm
content: Ok so if I want to upconvert to 130mhz, the ferrite has to be broadband for 0-200mhz kind? So would toroids from USB cables or ATX psu's do? Im just in a situation where I CANT order toriods ATM so I have to try and make do with what I can find.No one answered my question what is the function of these trifilar transformers, what exactly are they balancing everything I see on the subject just says 10 wraps around a blah blah toroid with no real explanation as to there function... I mean if I diyed and LCR meter that could shoot 130mhz through the trifilar what am I looking for here

author: Fank1
author_rank: Regular Contributor
timestamp: November 15, 2015, 10:38:53 pm
content: In order to achieve proper transformer action the impedance of the "1" winding must be at least 4 times the input impedance.If you are using it for a 50 to 1600 transformation then the "1" side must be 200 ohms at the lowest frequency of use.The binocular cores, like toroids have a preferred frequency range so you really need to know what material you are working with.Sometimes it's just not that easy.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: November 15, 2015, 11:00:18 pm
content: I guess what im asking is is there a way way I can find two random cores wind them up and then test them to see if they will work well or not.Also what makes the best transformer, bulky with large guage magnetic wire or small with thin wire? I would guess large wire with the least wraps possible is better since a DBDM is lossy mixer. Is there maybe a way to send RF through the thing and use the dongle to analyze DB, im guessing my 25mhz siglent scope wont help much....

author: LaserSteve
author_rank: Super Contributor
timestamp: November 15, 2015, 11:40:05 pm
content: PM me with your mailing address and I'll drop you a used Minicircuits level 7 DBM and some VHF 'roids in the mail. I'll toss in a VHF vco so you can learn how to mix things down to your 25 Mhz Scope. I just scrapped an ancient sat-phone so I de-soldered some useful stuff.Since your instrument blind, you might want to start with this, which is something I asked Chuck Wenzel for when I was a poor college student.http://www.techlib.com/electronics/detect.htmIts good up to 250 Mhz, but not much more. You might find a suitable diode in your package, too.You might need a choke to keep RF out of your DVM, back them VOM were more common.Merry RF Christmas,Steve

author: cdev
author_rank: Super Contributor
timestamp: November 15, 2015, 11:47:52 pm
content: Quote from: rwgast_lowlevellogicdesin on November 15, 2015, 05:08:22 amYou can't use a HF RF transformer up to 200 MHz. HF is basically 3-30 MHz. Look at schematics for your application. Lower frequencies require more turns. You learn a lot trying different approaches. Although you could also make an air core RF transformer, for HF you would need a lot more turns. I would figure out what impedance transformation you need (say from 50 or 75 ohms - to the input of the device you are using, if you know it.) But most important, don't worry that much for now, just get it working to start and then figure out the optimal matching transformer. In other words, just do it. If you can get your converter working so you can receive signals, then thats something to work with and the rest will be easier than you think.You should be able to find exactly what you need athttp://kitsandparts.com/toroids.phpfor very little money. Binocular cores work very well in that kind of application. Low loss /more power transfer. A regular toroid would be fine too. The smaller a toroid is, the cheaper the cost. #6 material is a good choice for many HF applications- So is #43 or #31However, # of turns and optimal material will vary a great deal depending on the impedance transformation desired and frequency.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: November 16, 2015, 02:34:30 am
content: @Cdev, ok im very confused at your statement. #6 toroids are what everyone who does diode ring videos use, im trying to upconvert to 125 or 130mhz..... Now that is considered my LO correct? Somone said the AM bars would work fine then someone else said they wont work with the high LO so that is where im super confused... Im thinking about just hooking up an oscillator to a diode ting with an antenna no transformers at all and see what happens lol. Its hard to experiment without a variety of parts.Ive ripped apart so many old 60/70s transistor radios and year 2000 range A/V receivers and have just not found any of the parts im looking for....

author: AF6LJ
author_rank: Unknown
timestamp: November 16, 2015, 02:42:15 am
content: Quote from: rwgast_lowlevellogicdesin on November 15, 2015, 11:00:18 pmIn a word No, that is like asking "I need a 10K resistor can I use any random resistor?"QuoteYour scope would allow you to see the output of the mixer, other than that; it wouldn't be of much help.You wouldn't even be able to see if your mixer was unbalanced, which can lead to other problems...

author: AF6LJ
author_rank: Unknown
timestamp: November 16, 2015, 02:43:58 am
content: Quote from: LaserSteve on November 15, 2015, 11:40:05 pmGood Going Steve

author: AF6LJ
author_rank: Unknown
timestamp: November 16, 2015, 02:46:59 am
content: Quote from: rwgast_lowlevellogicdesin on November 16, 2015, 02:34:30 amYour LO is yourLocal Oscillatorthe RF signal you are going to use to beat against the HF signals to get 6them up to VHF where your tuner will work for you.Sorry for the unexplained jargonj..

author: LaserSteve
author_rank: Super Contributor
timestamp: November 16, 2015, 03:58:49 am
content: What I send you will be a level 7 Doubly Balanced mixer from MiniCircuits Labs, most likely from theSBL or a SRA family in a metal can package.You'll need this chart to set the RF drive to the LO input.http://www.minicircuits.com/app/AN40-012.pdfIf you can find a copy at AbeBooks, Amazon, or get it at a library, you might like W7ZOI's book:Experimental Methods in RF Design.In most areas of the US, you would be hard pressed to find a library that does not have a ARRL handbook, either.Which is a very good starter textbook in RF. Especially older editions.Steve

author: cdev
author_rank: Super Contributor
timestamp: November 16, 2015, 03:27:44 pm
content: Quote from: rwgast_lowlevellogicdesin on November 16, 2015, 02:34:30 amYes. You won't need a toroid on the output. Basically you are building a "single conversion super-heterodyne" receiver.Just search on that term.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: November 16, 2015, 03:52:49 pm
content: Thank you very much laser steve, did u get my pm? I just want to make sure becuase my pm have nothing in the sent items....