Re: LF: RE: Analog oscillators

["Roelof Bakker" <roelof@ndb.demon.nl>]

Hello Stefan,

A FT-37-43 ferrite toroid is not suitable for a VFO as you found.
Powdered iron cores from Amidon are much better in this regard.
From the common available parts -6 material has the lowest temperature  
coefficient,
-7 is slightly better:

T-50-2: 95 ppm/C
T-50-6: 35 ppm/C
T-50-7: 30 ppm/C

The temperature coefficient does not vary with the size of the toroid.

There are tricks to achieve mechanical stable windings on a Toroid.
One is to wind it as tight as you can and than place the coil in boiling  
water for 10 minutes.
This removes the mechanical stress and the winding settles down.

73,
Roelof, pa0rdt