[TowerTalk] ferrites for Beverage transformers
jim at audiosystemsgroup.com
Mon Apr 10 12:53:08 EDT 2017
I don't consider myself an expert on this topic, but I just wound four
transformers for VE3DO loops using #43 cores that I had in my parts
stash. Winding guidelines were for binocular cores and a ferrite
material with greater mu, so I increased the number of turns by about
50%. They all work just fine. If all that I had were #31 cores I would
have used those instead. The key to this is knowing u' and u'' (u' is
mu, u'' accounts for the loss component) for the material. Fair-Rite
publishes this data for all of their materials as a graph of the values
as a function of frequency in a dozen or so pages near the front of
their excellent catalog.
One VERY important point that everyone seems to have missed in winding
these transformers is that stray capacitance between windings couples
common mode noise from the coax shield to the antenna, then back down
the coax to the RX as a differential signal.
A ferrite toroid has such a high mu that it contains virtually all of
the magnetic flux, so there is no need for one winding to lay on top of
the other, and doing so greatly increases the interwinding capacitance.
The transformers I wound are on opposite sides of the toroid core. I
used small gauge wire (#28?) from a hunk of multi-pair in my junk box.
73, Jim K9YC
On Mon,4/10/2017 9:08 AM, David Robbins wrote:
> I want to get some cores to be able to repair two wire Beverage transformers
> and reflection transformers. I have been reading this:
> http://www.qsl.net/n1eu/topband/BeverageXfmrs.htm and some other articles
> and trying to find the referenced parts, in particular the 412-5250
> binocular core sounds good for the impedance transformers, but google is
> failing me when trying to find a source. who stocks them?? I haven't seem
> much about reflection transformers either, would that same core be good for
> reflection transformers or what else is recommended??
> David Robbins K1TTT
> e-mail: <mailto:k1ttt at arrl.net> mailto:k1ttt at arrl.net
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