[Lowfer] Ferrite Toroid vs. Binocular Ferrite

[jrusgrove at comcast.net]

Stan

I don't typically use bifilar windings where primary to secondary isolation is important ... such as 
a noise mitigation requirement. For that application I prefer separate windings. Before binocular 
cores I would wind separate windings on each side of the core to keep primary to secondary 
capacitance at a minimum. This works fine in terms of isolation but adds to the transformer loss and 
severely restricts the usable bandwidth of the transformer. Since my requirements are usually for a 
limited frequency range at LF or MF, where gathering enough signal is seldom a problem,  it's 
possible to build a transformer that's 'okay'. The separate primary / secondary winding on a 
binocular core makes for a much lower loss and wider bandwidth transformer (than on the toroid) 
while keeping the C between windings at 10 pF or less.

As far as bifilar, the greater the number the number of twists per inch the lower the impedance ... 
although the change isn't that dramatic. There 's a chart in older Handbooks (1980 page 3-13 for 
example) that shows the impedance for a few different wire sizes and different number of twists per 
inch. More complete information might be available on the web - the ARRL measurements were made back 
in the mid 70's. For low impedance applications it's often necessary to parallel multiple pieces of 
bifilar to get the desired line impedance.

Jay

----- Original Message ----- 
From: "Stan, W1LE" <stanw1le at verizon.net>
To: "Discussion of the Lowfer (US, European, &amp; UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Wednesday, December 22, 2010 8:19 AM
Subject: Re: [Lowfer] Ferrite Toroid vs. Binocular Ferrite


> Hello Jay,
>
> Thanks for the details.
> I noticed that you had migrated to the binocular cores, on your K9AY
> array for lower freqs.
>
>
> Next question:
> I see some bifilar windings are made from twisting a pair of wires
> together before winding onto the core.
> Some bifilar windings are just parallel wires bonded together.
> Are there any performance advantages or disadvantages ?
>
>
> I hope every one on the Net is having the very best of this holiday season.
>
> Stan, W1LE     Cape Cod    FN41sr
>
>
>
> On 12/22/2010 6:17 AM, jrusgrove at comcast.net wrote:
>> It's been my experience that binocular cores make better broadband transformers ... lower loss 
>> and
>> wider bandwidth compared to toroidal cores. This is especially true when using conventional 
>> winding
>> instead of bifilar on toroids. The binocular primary to secondary capacitance usually comes in
>> around 10 pF ... which provides very good isolation at LF and VLF. If high primary to secondary
>> isolation is important line the binocular tubes with some sort of tubing - I use 'unshrunk' heat
>> shrink tubing. Some ferrite materials are rather conductive.
>>
>> Jay W1VD  WD2XNS  WE2XGR/2
>>
>> . ----- Original Message -----
>> From: "Stan, W1LE"<stanw1le at verizon.net>
>> To:<Lowfer at mailman.qth.net>
>> Sent: Tuesday, December 21, 2010 9:31 PM
>> Subject: [Lowfer] Ferrite Toroid vs. Binocular Ferrite
>>
>>
>>> Hello The Net:
>>>
>>> For the same ferrite material, what is the difference in the performance
>>> between
>>> a binocular and a toroid form factor ?
>>>
>>> My preliminary thinking is that the same pri and sec turns will yield
>>> the same bandwidth and performance  on either.
>>>
>>> What is the wisdom and experience ?
>>>
>>> Stan, W1LE      Cape Cod     FN41sr
>
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