[Amps] 160M PI network Toroidal Coil

[Carl]

Ive used 7 mix cores for SS VFO's that are rock solid. Dont use the smallest 
core you can squeeze the smallest wire on and use a Hi-C circuit.
They sure put out a clean signal on the SA compared to DDS.

OTOH trying to get stability with a slug tuned coil is damn near impossible 
without wasting a lot of time with TC caps.

Carl
KM1H


----- Original Message ----- 
From: "peter chadwick" <g8on at fsmail.net>
To: "Manfred Mornhinweg" <manfred at ludens.cl>
Cc: <amps at contesting.com>
Sent: Tuesday, October 08, 2013 3:36 PM
Subject: Re: [Amps] 160M PI network Toroidal Coil


> Manfred,
>
> it is interesting to look at the WW2 German radio equipment - obviously 
> designed pre-1939. The use of ceramics, especially in capacitors, and iron 
> cores is interesting, to say the least.
>
>>Nowadays of course I use DDS chips instead of VFOs, so that problem has
> been solved<
>
> Has it? unless all the spur and noise  powers summed in a 1 MHz bandwidth 
> are at least - IN THAT 1MHZ- average -110dBc/Hz - from
> 100Hz away from the frequency. You don't meet the requirements ot the 
> Radio Regulations.
>
> 73
>
> Peter G3RZP
>
> =======================================
> Message Received: Oct 08 2013, 07:26 PM
> From: "Manfred Mornhinweg" <manfred at ludens.cl>
> To: g8on at fsmail.net
> Cc: amps at contesting.com
> Subject: Re: 160M PI network Toroidal Coil
>
> Peter,
>
> > The numbers I've seen for flux density suggest that at 160m, you
> > should be at no more than 100 gauss or 10 mT for reasonable losses
> > and linearity.......and preferably a bit less.
>
> Yes, that's about correct. The exact value varies a bit with core
> material, size, and so on, but will be close to 10mT.
>
> This tends to require long, relatively slender cores, or very low
> permability ones.
>
> > So even if you cool the toroid, I'm still a bit doubtful about
> > linearity.
>
> So am I. But the emphasis is on "doubtful". I would have to try it, as I
> don't have good data about that material's linearity. Real saturation
> anyway only starts at much higher flux density levels. But hysteresis
> effects have a good chance to cause significant nonlinearity.
>
> > Plus there's the temperature coefficient to consider, too.
>
> As long as the loaded Q is low enough, that shouldn't become a real
> problem in a tank circuit. It's much worse when you are trying to make a
> VFO coil on an powdered iron core, as is often suggested in ARRL
> literature! In my youth I built several radios with "automatic built-in
> scanner" that way, until I figured out that nice big air core coils are
> far more stable!
>
> Nowadays of course I use DDS chips instead of VFOs, so that problem has
> been solved!
>
> > Fortunately, dust iron has a fairly high Curie temperature, but that
> > needs to be given some consideration - I suspect Amidon don't have a
> > figure for it.
>
> I think that the Curie temperature is probably high enough, so that
> insulation failure of the wire, or binder degradation of the core, are
> the limiting factors.
>
> > For some reason, I've never been a big fan of toroidal dust iron
> > inductors....
>
> They have their uses, where they provide some worthwhile advantage over
> other solutions. But they are certainly not an essential type of
> component. If all iron dust cores disappeared from this world, I could
> still design all my circuits, with only minor limitations, using either
> air core coils or ferrite cores, depending on the case. Instead if
> ferrite was taken away from this world, life would be much harder! Some
> kinds of circuits we are used to just couldn't be built.
>
> Manfred
>
> ========================
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> http://ludens.cl
> ========================
>
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