I also had a look at a book I about forgot I had named Ferromagnetic-Core
Design & Application Handbook, also by Doug Demaw. The part about 61 material
came up one time in a conversation with a tech at Palomar Engineers who
recommened it but at the time, we were speaking of something around 28 MHz. In
this book, it says due to low Permeability, 61 can be used at say 28-30 MHz and
should be used on up for frequencies on up to VHF, and UHF. For lower
frequencies below say 28-30 MHz, 43 material should be used because of it's
higher permeability. 63 has a lower permeability than 61 and would work worse
going lower but how much lower I don't know. The operating frequency range in
the chart for 43 material shows 0.01 to 1 MHz, but we know it's used higher in
RF power broadband transformers. Keep in mind I'm only thinking about broadband
RF power transformers, not narrowband transformers.
What he says is that to use the standard transformer equations to find the
maximum flux density or to find the cores area. The maximum flux density should
be kept below the start of the knee in the linear region. One would need a BH
curve of the material to see where the knee starts to bend to obtain the
maximum in gauss. Maximum flux density is generally at the top of the knee on
regular power transformers, but that is out of the linear region. I would think
operating within the linear region is what one would want for an RF transformer.
Best,
Will
*********** REPLY SEPARATOR ***********
On 2/3/06 at 3:25 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. 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. 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@contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>>
>>>>>
>>>>
>>>> Richard L. Measures, AG6K, 805.386.3734. www.somis.org
>>>
>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>
>>Richard L. Measures, AG6K, 805.386.3734. www.somis.org
>
>
>
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