On 21 dic, 17:42, Sébastien MEDARD wrote:
Hello,

On Tue, 21 Dec 2010 08:07:03 -0800, Wimpie wrote:
I think it is a good thing to contact some people locally.

I think I am prepared to do that

I had to use several ferrite cores to reduce the interference from 3.3
MHz to 15 MHz to an acceptable level. * The volume and weight of the
ferrite cores I used exceeds that of the adapter.

About ferrite cores and tapped coils.... I was wondering about
something...

Imagine a tapped coil from a inductance value, let's say "i". what is the
effect of progressively introducing a ferrite core (wand) inside the
tapped coil? Reducing, or increasing "i"?

We were speaking about a Collins receiver. If I read well, it seems to
use this kind of feature. Could be better for experimentation, no?

Sebastien.

p.s. I need to buy something to measure capacitance and inductance (RLC
bridge...).

Hello Sébastien,

When you put in a ferrite bar of suitable material, the total
inductance will increase. The longer and thicker, the more will be the
increase of inductance. The actual increase depends on several factors
(length/diameter ratio of coil, and to a lesser extend, ferrite
magnetic permeability).

When I put 10*150mm^2 ferrite rods (from old vacuum tube AM/FM radios
I believe) into my simple single capacitor preselector, the lowest
frequency goes down from 3.4 MHz to 1.1 MHz. The 5 m wire outside
wire performs equal w.r.t. my small portable indoor loop on AM BC
1476, 1485 kHz (Spanish stations). Of course, loop positioned and
oriented for best reception.


When you look into the technical documentation of ferrite producers/
vendors (Ferroxcube, Fairrite, Amidon, TDK, Epcos, Kitagawa, etc),
they will show you a graph that relates inductance change ratio versus
coil dimensions and ferrite permeability. Wrong choice of ferrite
material will reduce Q-factor significantly.

The effect on a tapped coil in a circuit depends also on where you
start pushing the bar into the coil, as the part of the coil closest
to the ferrite bar changes inductance first.

Regarding LCR meter, There are some very nice kits around that
measures small inductors and capacitors very well:
http://electronics-diy.com/lc_meter.php gives an example.


Best regards,



Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me