289	2007-01-02 03:01:49	neomag_magneo	Transformers for H-mode mixers: a question
Message	Date	From	Subject
Dear group, Just received my copy of EMRFD, which has (among some other things !) a chapter of the H-mode mixer. Although this topic has been discussed in the group previously, a particular question has been bothering me... I started my experimentation with H-mode mixer some years ago, using the FST3125 chip available at that time and with three transformers. I constructed mine using Ferroxcube 9-mm toroids (pink) with mu = 800 , in my opinion it is equivalent to FT37-43. I did each one with trifilar windings, one winding for the primary and the two others connected in series to make the secondary with center tap. Ever since, all the published schematics and articles on H-mode seem to apply binocular balun formers only. I wonder if there is something wrong with the toroid approach, at least the many diode DBMs constructed by W7ZOI and others use this kind of transformers. About the book, after one week of studying I have found the material excellent. Having spent more than 25 years with its predecessor (SSD), I would expect at least a similar period with the current one ! Another question yet: I think there was a number of errors at least in the very first printing of the EMRFD. Is there a list of errata somewhere, or, has the most recent copy been corrected yet ? 73 de Heikki (OH2LZI)
290	2007-01-02 05:29:07	Mike Czuhajewski	Re: Transformers for H-mode mixers: a question
You can find EMRFD errata on the W7ZOI web page; here's the direct entry point-- http://users.easystreet.com/w7zoi/em0.html And, needless to say, you should also look around the rest of the site since there's a lot of good info there!
291	2007-01-02 05:54:42	w4zcb77	Re: Transformers for H-mode mixers: a question
I > constructed mine using Ferroxcube 9-mm toroids (pink) with mu = 800 , > in my opinion it is equivalent to FT37-43. I did each one with > trifilar windings, one winding for the primary and the two others > connected in series to make the secondary with center tap. Ever since, > all the published schematics and articles on H-mode seem to apply > binocular balun formers only. I wonder if there is something wrong > with the toroid approach, at least the many diode DBMs constructed by > W7ZOI and others use this kind of transforme 73 de Heikki (OH2LZI) > The FT37 cores will work in the "H" mode with the FST 3125 mixers, although there might be some reduction in IP3 levels tolerated by the circuit due to the ferrite. Typical IMD levels attained with the binocular cores has been in the +40, +45 dBm range and the smaller cores may not be immune to nonlinearities at these levels. I don't know of any measurements made with other cores except for the ones in the MCL transformers, those are definitely toroidal NOT binocular, and work well. The TT4-1A's are somewhat better in the IMD department, and are slightly lower loss than the conventional T4- 1's as well. But MCL has always poured some magic in their transformer ferrites and they're not talking. Absolute balance is helpful in extracting the best performance with the 3125 mixer, careful symmetry in your transformer construction as well as construction layout will pay off. W4ZCB
292	2007-01-02 09:10:54	Graham Haddock	Re: Transformers for H-mode mixers: a question
Heikki: Either toroids or binocular cores can be made to work for most broadband transformer circuits. Some people find that for a small number of turns, the binocular cores are easier to handle and wind consistently, and the transformer can be made smaller.