[Amps] confused reading amidon ferrite specs?

[Will Matney]

Dan,

*********** REPLY SEPARATOR  ***********

On 3/7/06 at 5:55 PM Dan Sawyer wrote:

>Should mix 67 support a 1.8 to 55 MHz 1200 watt transformer?


I'd give Amidon or Fair-Rite a call or an e-mail and ask them their recommendation.


>
>On this topic:
>    1. What physical form should be used?


Just stack two sets of toroids side by side like everyone does. You'll need tow pieces of 1/4" dia. brass tubing and some PC borard to make them up along with some teflon covered hookup wire.


>    2. What is a reasonable turns on the 50 Ohm side (to start design).


Well, it's according to what the base and collector impedance is of the transistor you plan to use. It's generally listed on their spec sheets. Take that impedance and multiply it by two (for two transistors) to get the total impedance. Then divide that by the line impedance which most likely is 50 ohms. The ratio you get from that most likely will either be 16:1 or 9:1. Take either 9 or 16 and get the square root of that, and that is the number of turns for the wire (4 or 3). The other one is only one turn by the tubing. Then you need to multiply the line impedance by at least 4 to get the reactance for the transformer which for 50 ohms is 200 ohms and is what about all uses. Then figure the inductance of the coil by the number of turns and the AL value from the number of toroids you'll have. You have to have the inductance (L) to check the reactance as XL =  2 pi F L. You need enough core together to equal this. A check that you have enough core should be done to see that your below the maximum flux density also by using the standard flux density formula. Ferrite has a rather low flux density, something around 1500 gauss (according to what material). For a 100 watt set, the usual stack lengths are 1/2" long for the input (for about 10-20 watts PEP in), and about 2" long for the output using 1/2" OD by 1/4" ID by 1/4" thick toroids. If I used 43, I'd make that 2" length a little longer, maybe 2-1/2" which will help it not get as hot. One other place to get some info would be CCI here in Ohio (Communications Concepts Inc.). I think they have the old Motorola app notes there they use.

http://www.communication-concepts.com/


>
>Dan
>
>R at contesting.com;Measures wrote:
>
>>On Mar 7, 2006, at 9:03 AM, Jim Brown wrote:
>>
>>  
>>
>>>On Tue, 7 Mar 2006 08:56:08 -0800, R at contesting.com;Measures wrote:
>>>
>>>    
>>>
>>>>On an oscilloscope, using 100w of RF, I observed that mix #61 begins 
>>>>to
>>>>distort the waveform at c. 13MHz.  Those who don't desire to generate
>>>>harmonics should probably follow the manufacturer's specs and not
>>>>operate 61 above 10MHz.
>>>>      
>>>>
>>>The distortion and losses will depend on many variables, including the
>>>power level, the size of the core, and the number of turns.
>>>    
>>>
>>
>>Agreed.  Waveform distortion is the result of of a combination of too 
>>many Webers and too much f.
>>
>>  
>>
>>>What were your
>>>test conditions (core size, turns, etc.)?
>>>    
>>>
>>
>>I don't remember the details, Jim, however, as I recall it was a 2.4" 
>>mix-61, mu=125,  core for a 450-ohm 8170 grid terminator R.  Whereas 
>>everything looked wonderful on  the 'scope at 1W, at 100W, it did not.  
>>After I read Permag Pacific's tech specs on mix-61, it was apparent 
>>that the seller didn't.  As a result of seeing the harmonic distortion 
>>above 13MHz with 100W, I switched to mix-67 (mu=40, rated by mfg at 
>>80MHz max) and observed a clean sinewave at 29MHz.
>>  
>>
>>>Jim Brown K9YC
>>>
>>>
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>>>http://lists.contesting.com/mailman/listinfo/amps
>>>
>>>
>>>    
>>>
>>
>>
>>
>>Rich Measures, 805.386.3734, AG6K, www.somis.org
>>
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>>  
>>
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