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