[Amps] Guidelines.....toroids for tank ckts

[Carl]

Scotch 27 Jeff.

Carl
KM1H


----- Original Message ----- 
From: "Jeff Blaine" <keepwalking188 at yahoo.com>
To: <jim at audiosystemsgroup.com>; <amps at contesting.com>
Sent: Saturday, March 24, 2012 7:16 PM
Subject: Re: [Amps] Guidelines.....toroids for tank ckts


> Dave,
>
> For the low bands, the #2 red is pretty widely used.  The 3M tape for that
> (forget the number) is pretty expensive but it's strong and won't 
> breakdown
> in moderate heating.  For the higher bands, air core types are small 
> enough
> to fit even into some tiny spaces so there's typically no good reason to 
> put
> up with the compromises (lower Q and heat loss) that a toroid necessary
> involves.
>
> The big mistakes made on these are trying to use a single toroid for 2
> bands - as Carl says below, one toroid - one band.  And not providing any
> consideration for heating if you are into high duty cycle modes like RTTY.
> You can find a lot of comments on both of these issues in the last couple 
> of
> year message history.
>
> 73/jeff/ac0c
> www.ac0c.com
> alpha-charlie-zero-charlie
>
> -----Original Message----- 
> From: Jim Brown
> Sent: Saturday, March 24, 2012 6:08 PM
> To: amps at contesting.com
> Subject: Re: [Amps] Guidelines.....toroids for tank ckts
>
> On 3/24/2012 3:24 PM, Carl wrote:
>> I would not recommend toroids above 40M and even there its iffy at high
>> power. And of course use one per band.
>
> Yes. I don't know anything about powdered iron materials, but all
> ferrites get increasingly lossy with increasing frequency.  A few
> ferrite mixes are designed to handle high power, and are pretty low loss
> at low to medium frequencies, but each of them has a high frequency
> limit, beyond which their loss has increased to the point that they are
> not very useful.  For example, Fair-Rite #61 starts getting lossy above
> about 10 MHz, while their #67 starts above 20-30 MHz.  In general,
> losses will couple from the core to the wires, and will show up in the
> equivalent circuit as resistance.
>
> Another issue is voltage breakdown -- ferrites are semi-conductors, and
> each mix is different there too. Some are pretty good insulators, others
> are fairly conductive.  It's worth studying the Fair-Rite catalog, which
> is really excellent. Fair-Rite data sheets include data for resistivity,
> permeability and permittivity. If you have a solid EE background, it's
> also worth calling Fair-Rite's technical support people. But study their
> catalog and applications notes first so that you know what questions to
> ask and can understand the answers.
>
> 73, Jim K9YC
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