Hi Gary,
A second winding in series that cancels the DC would also cancel the AC
rendering the part... useless. A second winding with only DC is indicated, and
with minimal coupling to the main winding therefore, the single turn idea.
By making the choke sufficiently high value the RF current will be very
small, on the order of 1% of the total in the plate circuit, so that the core
distortion is not a significant factor.
73 & Good morning,
Marv WC6W
http://wc6w.50webs.com/
--- On Thu, 1/14/10, Gary Schafer <garyschafer@comcast.net> wrote:
> From: Gary Schafer <garyschafer@comcast.net>
> Subject: RE: [Amps] (Perhaps) A plate choke too far ...
> To: "'Radio WC6W'" <wc6w_amps@yahoo.com>, amps@contesting.com
> Date: Thursday, January 14, 2010, 6:51 PM
> 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/
> >
> >
> >
> >
> >
> >
> >
> > *
> >
> >
> >
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
>
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