EMRFD Message Archive 289
Message Date From Subject 289 2007-01-02 03:01:49 neomag_magneo Transformers for H-mode mixers: a question 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
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 withsince,
> trifilar windings, one winding for the primary and the two others
> connected in series to make the secondary with center tap. Ever
> all the published schematics and articles on H-mode seem to applyby
> binocular balun formers only. I wonder if there is something wrong
> with the toroid approach, at least the many diode DBMs constructed
> W7ZOI and others use this kind of transforme73 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.
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.