[Amps] RF Chokes

[Will Matney]

Hal,

See below;

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

On 7/19/06 at 9:31 AM Harold  Mandel wrote:

>Yesterday, W1ITT mentioned his chokes are hollow Teflon, filled
>with a "particular" ferrite filling.
>
>I wonder if the use of the word "particular" refers to the 
>meaning "particle-matter," or " a specific variety?"


Probably the variety or type of powder used. The thing is, ferrite is a magnetic ceramic.

>
>
>In asking this, does anyone have experience with ferrite powders
>filling such devices? Is it possible to formulate a ferrite core
>starting with powder and something like a chemical eutectic?
>
>Can just ferrite powder without a binder work?


In my opinion, not very good at all. The hysteresis loop characteristics would be terrible. The frequency stability 
wouldn't be worth a hoot either. The particles wouldn't be in intimate contact with each other which they are when 
molded into shape. If you remember, steel is even re-rolled and re-anealed to get the crystaline structure of cold 
rolled grain oriented steel like Hipersil. Ferrite is molded from a mixture, heated in a furnace, and cooled. This 
brings the particles into intimate contact and holds them in place. Also, ferrite can be mixed different as to the type.

Below is a link to a patent and a quote from the book, Practical RF Communications Data by Doug DeMaw.

Quote;

"Expansion and contraction of the ferromagnetic material will cause unacceptable changes in inductance when
frequency stability is an important design parameter".

Also see this patent whhich shows what happens with hysteresis loop characteristics when even toroids are stacked
and do not mate intimately. Loose powder would cause the same. You may have to create an account to read the
complete patent. It's free though.

http://www.freepatentsonline.com/4007541.html?s_id=2efa31c42518279271b4aec6cdf3f5f8


>
>Hal
>W4HBM
>
>
>-----Original Message-----
>From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
>Behalf Of Kenneth D. Grimm, K4XL
>Sent: Wednesday, July 19, 2006 9:09 AM
>To: wc6w at juno.com
>Cc: philc at texascellnet.com; amps at contesting.com
>Subject: Re: [Amps] RF Chokes
>
>wc6w at juno.com wrote:
>>> -- "Phil Clements" <philc at texascellnet.com> wrote:
>>>     
>> <snip>
>>
>>   
>>> Harris has been doing this for years in their amps. The RF->110, 
>>> (pair of 4CX1500B's) has a plate choke that is a very small ferrite 
>>> loaded unit that is clean from 1.8-30 mhz. This was the ideal fix 
>>> for adding WARC bands and 160 meters, but the amateur amp 
>>> manufacturers did not pick up on this.
>>>
>>> <snip>
>>>
>>>     
>>> (((73)))
>>> Phil Clements, K5PC
>>>     
>>
>>   
>
>Would it be possible to have a look at the photos that you took of the 
>choke and parasitic suppressor arrangement that you posted on  
>www.pixhost.com/pixp/philk5pc/Platechoke.jpg but which are no longer 
>available?
>
>> Hi Phil,
>>   If I recall correctly, that choke is listed on the schematic at 
>> 115uH.
>>
>>   Employing the ferrite core should place the first (parallel) 
>> resonance suitably above 30 MHz.
>>
>>   This appears to be a valid approach because of the low plate 
>> impedance (circa 1000 ohms).  Though there will still be plenty of 
>> reactive current through that choke on the lowest bands.
>>
>>   Still a compromise, albeit a less objectionable one than 
>> most "amateur" amps.
>>
>>   I'm feeling just a bit of deja vu all over again. :-)
>>   To see why, start at this old link:
>>
>>    http://lists.contesting.com/_amps/2000-03/msg00603.html
>>
>> 73 & Good evening,
>>   Marv WC6W
>>
>> http://wc6w.50webs.com/
>>
>>   
>Actually, it makes pretty good reading...all over again.   ;-) 
>
>
>73,
>-- 
>
>Ken K4XL
>k4xl at arrl.net
>
>*** BoatAnchor Manual Archive ***
>On the web at http://bama.sbc.edu and http://bama.edebris.com
>FTP site info: bama.sbc.edu login: anonymous p/w: youremailadr
>
>_______________________________________________
>Amps mailing list
>Amps at contesting.com
>http://lists.contesting.com/mailman/listinfo/amps

Best,

Will