On 17 dic, 16:28, Sébastien MEDARD wrote:
Hello,

On Thu, 16 Dec 2010 09:40:15 -0800, Wimpie wrote:
Hello Sébastien,

This: *http://www.tetech.nl/divers/Simple_H...ctor1.png*will help
you. It shows the basic idea of a simple single variable capacitor
preselector.

Many thanks. I will try it as soon as possible.

You can use one coil and put two selectors on it, but with two seperate
coils the attenuation for out-of-band signals is much better. This is
because the individual turns of each coil have low mutual coupling (they
don't act as a transformer). * As I have sufficient antenna noise, the
selectors (in my case clips) are mostly on the lowest position (I don't
need matching to get more signal and noise).

OK.

For AM BC operation you need more turns (w.r.t. the coils on the photo)..

As I want to use it from 0.5 to 30MHz, what would be size of both coils?
How many turns? What diameter? What would be the value of the C1
capacitor? A lot of questions....

Thanks again.

Sebastien.

Hello,

Do you have some background in electronics and/or AC circuits (concept
of reactance, impedance, resonance, etc)?


Wim
PA3DJS

Hello,

On Sat, 18 Dec 2010 08:09:52 -0800, Wimpie wrote:

Do you have some background in electronics and/or AC circuits (concept
of reactance, impedance, resonance, etc)?

I should.... But I was better in chemistry I should have studied RLC
circuits but at this time it was boring... If I had some interest in
shortwave listening, I would have been a better student in physics

But I should be able to understand I think I am going to see if there
is any radio club near the place I live. Because I have a lot of
questions and English is, as you understood it, not my main spoken
language

Seb.

On 19 dic, 23:10, Sébastien MEDARD wrote:
Hello,

On Sat, 18 Dec 2010 08:09:52 -0800, Wimpie wrote:
Do you have some background in electronics and/or AC circuits (concept
of reactance, impedance, resonance, etc)?

I should.... But I was better in chemistry I should have studied RLC
circuits but at this time it was boring... If I had some interest in
shortwave listening, I would have been a better student in physics

But I should be able to understand I think I am going to see if there
is any radio club near the place I live. Because I have a lot of
questions and English is, as you understood it, not my main spoken
language

Seb.

Hello Sébastien,

I think it is a good thing to contact some people locally.

Besides support with the calculation for the inductors and capacitors,
small "construction errors" can degrade performance of a basically
good design significantly.

Be prepared to get many different answers to the same question!

Yesterday evening I experienced strong increase in mains supply
synchronized interference. After some elimination tests, the
"offender" was a new tiny switching plug-in adapter.

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.

Best regards,


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

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...).

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

Hello,

On Fri, 17 Dec 2010 09:20:48 -0800, Richard Clark wrote:

Reg Edward's software, that you already have access to, will answer that
far faster than asking here. Reason for that is because of all the
variables that come into play. You can judge for yourself when you
enter them into the program and observe what results are returned.

Tonight and yesterday night I played with my experimentation board
(loop...s on my shelves).

I have a 4 loops (square) web :
1 - 8 turns - 1.5 m /side
2 - 3 turns - 1.0m /side
3 - 1 turn - 0.8m /side
4 - 1 turn- 0.65m /side

Each one is inside the other one.

I used the second to be the matching one from the previous, the firts.
The third, to be the mathcing one of the second, etc.

The resonant one gets a variable air capacitor (I change it every time I
need to go higher....).

Very interesting, indeed.

If I understand well, the loop gets the role of inductance and the
capacitor the role of the capacitance... (Lapalisse...). Matching both
gets the best result for a given frequency. I succeed in making apparent
signals that I was not aware of... With this antenna I can tune in the
frequency from 300 KHz to near 7300 KHz... Completely amazing. That's the
first time I can exactly see (thanks to the waterfall information
display) how it does increase, not only the signal, but what's more
important, the signal/noise ratio. I understand now how this is very
important...

What I can see, is that depending on the size of the loop and the
frequency I am monitoring, the variable capacitor may or may not be very
difficult to use, and the bandwidth lack of noise, narrow or wide...
Interesting to see that it is possible to increase the signal without
increasing a lot the signal/noise ratio (better than nothing . But you
can't play when the signal is too weak....

I am quite happy. It does not tell anything about the antenna efficiency,
but it helps me understand how it works. I get somebody in my family who
is a physics teacher... I need to ask her information about "RLC
oscillators for newbies" to be able to put some rational things upon my
experimentations

To do next :
- Try to carry out the tiny preselector from Wim (need to find some coper
wire... And need to try to recover some old radio parts to play with....
(get some ferrite rods, low value variable capacitors, etc.)
- Try to get some time, and some place, to play with long wires, dipoles
and their related matching systems...

Sebastien.