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@fsmail.net>
To: "Manfred Mornhinweg" <manfred@ludens.cl>
Cc: <amps@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@ludens.cl>
To: g8on@fsmail.net
Cc: amps@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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