Jim
The Collins equipment used this method in their VFO'S, permeability tuning
also ferrite slug tuned IF transformers have been around for a long time.
There seems to be some confusion about Variometer. A Variometer consists of
two coils in series with one rotated within the other to vary Inductance
whereas a ferrite moveable rod inserted inside a coil is referred to as Slug
Tuning.
mal/g3kev
----- Original Message -----
From: "James Moritz" <[email protected]>
To: <[email protected]>
Sent: Tuesday, August 16, 2011 7:17 PM
Subject: LF: Re: ferrite coil
> Dear Mal, LF Group,
>
> >Instead of winding a tight coil on to a ferrite rod to get 270 uH and
> >tuning with a 250 p variable capacitor...
>
> The required tuning capacitance would be about 5000pF.
>
> >...instead wind an air core coil and move the ferrite rod into/out of
coil
> >for the required inductance necessary for frequency >of interest. This
> >would further reduce losses.
>
> You could tune inductance downwards in this way, but unfortunately any
> reduction would be accompanied by reduced magnetic flux due to the
received
> signal in the antenna winding. So the signal amplitude would be reduced.
> Also, I doubt if losses actually would be lower - certainly, the coil
> without the ferrite rod will have a much lower Q than with the rod in
place,
> so a point must come as the rod is withdrawn where Q decreases rapidly.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>
>
>
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