Marv,
You need a push pull choke. :>)
Maybe a second winding that loops back on the core and is in series with the
choke winding.
But I don't think that the DC current is the whole problem with ferrite.
There is the non linearity issue with RF current that will generate IM
products as well.
73
Gary K4FMX
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Radio WC6W
> Sent: Thursday, January 14, 2010 8:34 PM
> To: amps@contesting.com
> Subject: Re: [Amps] (Perhaps) A plate choke too far ...
>
> No one appears to have addressed my original query re: servo
> cancelling the DC in a toroid core. Rather wandering back to the
> general plate choke topic... So, I'll wander a bit too!
>
> While experimenting with all those chokes, one of the curious things I
> noticed was that if I took a large ferrite washer (4.4 cm dia. x .4 cm
> thick of unknown material) and placed the flat side adjacent to a 70uH
> solenoid wound coil (3" of B&W 3016), it almost completely dampened the
> series resonances (first one circa 25 MHz)!!
>
> I went looking around the 'net for an explanation and found US patent
> #3,835,370 that states that this effect is well known!
>
> The magic washer exhibits rather high resistivity (circa 10^7 ohms per
> cube) and is only weakly attracted by a magnet. Otherwise, it looks
> like plain ol' ferrite though, it is unlike any other core material in
> my inventory. It is also very low mu -- 32 turns of wire produced only
> 3uH! Anyone know what material this might be??
>
> I'd wager that this scheme could be usefully employed with almost any
> stock solenoid plate choke to eliminate those pesky resonances.
>
> Further searching found #3,982,814 & #2,692,372 both of which use a
> secondary Nichrome winding to similar effect!
>
> A final point of interest: #3,980,975 employing concentric coils. I
> tried this with a pair of B&W coils and it kinda of worked. A bit of
> judicious turns counting and positioning may be in order.
>
> Note: Patents may be easily downloaded via: free.patentfetcher.com
>
> 73 & Good evening,
> Marv WC6W
>
> http://wc6w.50webs.com/
>
>
>
>
>
>
>
> *
>
>
>
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