> -----Original Message-----
> From: Tom Rauch [mailto:w8ji@contesting.com]
> Sent: Wednesday, November 10, 2004 11:24 AM
> To: jmaass@columbus.rr.com; Jim Brown; TopBand List
> Subject: Re: Topband: 160m noise
>
>
> > I'll defer to your experience. Given the availability
> > of #43, #61, #73, or #77 toroids (all of which are
> > commonly available), which would be your first
> > choice? (Fair-Rite also recommends #31, but it
> > does not appear to be available in toroid form).
>
> Jeff,
>
> First remember the number order is sometimes random, a
> higher number does not always reflect higher permeability.
>
> When soft iron materials are made larger than a certain
> physical thickness and diameter, they exhibit internal
> effects that render them useless as suppression devices.
> It's similar to the velocity factor in dielectrics. make
> them big enough and impedance drops.
>
> That's why you only find higher permeability cores in
> smaller sizes.
>
> 31 43 and 44 material are about the limit for larger cores
> like common snap on cores.
>
> The optimum core to use "randomly" would be one that appears
> as a pure resistance and the highest possible resistance for
> the size you need. That's why you have to, as Jim often
> suggests, look at the manufacturer's catalog.
>
> Permeability and resistance also change with frequency. It
> is possible to have too much permeability (case in point,
> the cores suggested by Misek for Beverages) and actually
> wind up requiring more turns than a lower ui core.
>
> BTW, Amidon is a retailer and distributor. NEVER rely on
> second hand information. Go right to Fair-Rite's data.
>
> I've found multi-turn cores to peak at the mid HF range with
> 43 material, but again it depends on how many turns.
>
> 73 Tom
>
I appreciate the education from you and from Jim (and I'm
eagerly awaiting his promised article!)
I'd missed the shifting of the impedance peak downward
in multi-turn suppression apps. I'd looked at the Fair-Rite
Technical Information document at:
http://www.fair-rite.com/CUP%20Paper.pdf
On page 8 is Figure 22, which shows the Impedance vs
Frequency curves for one, two and three turns on a #43
core. I'd like to see similar graphs of other core materials
to compare.
It looks like several more turns than three are required
for use on 1.8 MHz to get >800 ohms with #43 material cores.
What number of turns have you used and measured?
73,
Jeff Maass K8ND
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