Jim:
Thank you for the reference.
Indeed, the self-resonant frequency of the typical small (FT50 size)
chokes I've wound are in the 5-10 MHz range, but at 100 MHz some
(depending upon the core material) still show enough Z to be useful.
For truly wideband 10 KHz - 100 MHz choke action, it's necessary to
series two wound with different core material and turns, e.g., 35 turns
on Steward 40 material for the 2.5 mH, followed by, e.g., 10 turns on
FairRite 43 material for > 50 MHz.
You have to pay particular attention to the u' and u'' values of the
ferrite material and how they change with frequency as this is a case
where core loss at high frequencies can be good.
Jack K8ZOA
Jim Brown wrote:
On Wed, 30 Jul 2008 20:33:53 -0400, Jack Smith wrote:
Yes, I have several ferrite core 2.5 mH chokes here, including the
Hammond one you mention. There's a significant difference in high
frequency performance of the pi wound on ceramic form versus the smaller
pi-wound over ferrite and that's one of the things I'm hoping to
illustrate in the article.
The RFI and Ferrite tutorial on my website includes clear explanations of
the nature of ferrite materials from a circuit point of view. You may find
it helpful in explaining why your very correct in your analysis. You are
welcome to cite it as a reference.
http://audiosystemsgroup.com/RFI-Ham.pdf
However -- ANY 2.5 mH choke has a good chance of looking capacitive at 50
MHz.
73,
Jim Brown K9YC
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
_______________________________________________
Elecraft mailing list
Post to: [email protected]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
