[Amps] Queation on toroid core materials

Sat Feb 4 11:11:12 EST 2006

On Feb 3, 2006, at 12:25 PM, Will Matney wrote:

> Rich,
>
> I went and read some of the book "Practical RF Communications Data" by 
> Doug Demaw on this. Below is a quote;
>
> "The type of core material used will depend to a great extent on the 
> required bandwidth of the transformer. For commercial frequencies 
> vetween 2 and 35 MHz, a permeability of 950 is satisfactory.

hogwash.  The mfg rates it at c. 1MHz.

> Because of the poor high frequency characteristics of this kind of 
> core material, the core disappears electrically (and gradually) as the 
> operating frequency is increased.

On a 'o-scope, the distortion is obvious.  Demaw should have looked.

> The benefit is realized toward the low-frequency portion of the chosen 
> bandwidth where the high permeability permits a minimum number of 
> transformer turns: The smaller the number of turns, the lower the I^2R 
> losses. It can be seen from the foregoing that low-frequency, 
> high-permeability core material is quite ideal for use in broad-band 
> transformers.
>
> Permeability factors of 40 and 125 also are popular for broadband 
> transformers operating in the HF spectrum at VHF and at UHF. The 
> frequency ratings of these cores, respective to efficiency, are most 
> suitable for for narrow-band transformers operating from 6 to 30 MHz 
> in tuned circuits."
>
> Now, those two permeability factors are 40 for 63 mix, 125 for 61 mix, 
> and 950 is for 43 mix.
>
> For all interested I found this. A general rule of tumb on designing 
> wide-band transformers is that they need to have a reactance of 
> approximately 4 times the load impedance. so for 50 ohms, that would 
> be 200 ohms.
>
> Best,
>
> Will
>
> *********** REPLY SEPARATOR  ***********
>
> On 2/2/06 at 11:17 PM R. Measures wrote:
>
>> On Feb 2, 2006, at 8:15 AM, Will Matney wrote:
>>
>>> Rich,
>>>
>>> *********** REPLY SEPARATOR  ***********
>>>
>>> On 2/2/06 at 2:14 AM R. Measures wrote:
>>>
>>>> On Feb 1, 2006, at 12:24 PM, Will Matney wrote:
>>>>
>>>>> All,
>>>>>
>>>>> What has been your experience in the wide-band transformer core
>>>>> material types available for use on 160-10 meters in both Ferrite,
>>>>> and
>>>>> Iron Powder, or the types recommended to use? Available materials
>>>>> that
>>>>> have been used in Ferrite is 43 and 61 material with 43 material
>>>>> having the highest permeability of about 850u. 43 was recommended 
>>>>> by
>>>>> Motorola in their HF amp designs for wide band transformers. 
>>>>> However,
>>>>> 61 was recommended to me once because of the 43 material heating
>>>>> quicker, or saturating, and the heat ruining the core. 61 was
>>>>> supposed
>>>>> to cure this but with a loss of permability.
>>>>
>>>> 61 begins to saturate at c. 13MHz, so the 10MHz max rating is
>>>> realistic.  63 is rated for up to 50MHz.
>>>>
>>>
>>> That;s what I thought too until the Guys at Palomar Engineers
>>> mentioned using 61. Below is from Amidon;
>>>
>>> Material 61 (µi = 125):
>>> Offers moderate temperature stability and high 'Q' for frequencies 
>>> 0.2
>>> MHz to 15. MHz.
>>
>> I've swept it, and at 15MHz the sinewave is badly distorted. This 
>> means
>> it generates harmonics.
>>
>>> Useful for wideband transformers to 200 MHz and frequency attenuation
>>> above 200 MHz. Available in toroids, rods, bobbins and multi-aperture
>>> cores.
>>>
>>> Material 63 (µi = 40):
>>> For high 'Q' inductors in the 15 MHz to 25 MHz frequency range.
>>> Available in toroidal form only.
>>>
>>> Material 43 (µi = 850):
>>> High volume resistivity. For medium frequency inductors and wideband
>>> transformers up to 50 MHz. Optimum frequency attenuation from 40 MHz
>>> to 400 MHz. Available in toroidal cores, shield beads, multi-aperture
>>> cores and special shapes for RFI suppression.
>>>
>>> So 43 wouldn't be any good for 6 meters at all, they'd have to use
>>> looks to me like 61.
>>
>> Not to me
>>
>>> However, if 61 saturates at 10-13 MHz, what do you use? Would you use
>>> a larger stack than normal to keep it from saturating or is 10-13 MHz
>>> it's maximum limit regardless of the literature?
>>
>> 61 is bad news above its 10MHz mfg rating.
>>
>>> That's my problem, what to spec as I may have to leave out ferrite
>>> transformers all together from the app if I cant resolve this. One
>>> place I hear one thing, and one another. Seems like I have never seen
>>> a source for ferrite or iron powder yet on the net, or in literature
>>> that I can trust.
>>>
>>>
>>>>> Also, in wide band transformers, the upper frequency limit is said 
>>>>> to
>>>>> be 10X higher, is this the same for iron powder the same as 
>>>>> ferrite?
>>>>> In iron powder, the recommended types in color are Red (mix 2), 
>>>>> White
>>>>> (mix 7), and Yellow (mix 6). Mix 2 is .25 to 10 MHz, Mix 7 is 1 to 
>>>>> 20
>>>>> MHz, and Mix 6 is 2 to 30 MHz. The permeability between the three 
>>>>> is
>>>>> not much different so I would think using mix 6 (Ye
>>>>>  llow) would be the way to go but loose a small amount of
>>>>> permeability. If the X10 freq rule holds true for iron powder, then
>>>>> one could use Mix 2 (red) easily enough and gain it back. 
>>>>> Generally,
>>>>> in any transformer, the upper freq. is not the problem, it's trying
>>>>> to
>>>>> use a core below its maximum lower frequency. That would hold true
>>>>> for
>>>>> either iron powder or ferrite I would think. What would any here
>>>>> recommend? This is for the RF transformer part of the software I'm
>>>>> writing.
>>>>>
>>>>> Best,
>>>>>
>>>>> Will
>>>>>
>>>>> _______________________________________________
>>>>> Amps mailing list
>>>>> Amps at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>
>>>>>
>>>>
>>>> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>>>
>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
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>>>
>>
>> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
>
>
>
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>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org