On 09 Dec 2010 17:11:54 GMT, Sébastien MEDARD wrote:

http://www.n0ss.net/qrp_1-1_w2du_coaxial_balun.pdf

That's the first thing I will do. Ferrite ordered

Hi Sébastien,

Good first step.

http://www.mfjenterprises.com/man/pdf/MFJ-902.pdf

Seems not so simple for me.

I see two things on the schematic :

- 2 variable capcitor and an inductance on the center

Good.

- A balun for balanced line (ie dipole????)

Yes.

As I already get a balun for dipole could you confirm that I just need the
center part of the schematic?

Confirmed, yes.

If the answer is yes, if I understand the schematic well, both of
variable capacitors are put one after the other inserted into the line.
The big question is how to make the variable inductance? Some wire wired
on a ferrite rod? (L ----------- A????) with a selector? Are the number
of half-loops means the number of turns?

Making the coil is easy. It is just bare wire. You connect leads
between various turns in the coil and a switch. A three to five
position switch will work. You can even wind separate coils and put
them on the switch so they add up in series as you turn the switch.

Even there, with a good
switching design you could use the same components to build them too.
(I am thinking of PI configuration, L, and so on).

What is the influence of these different configurations?

Some antennas (I am speaking of their wavelength, not style like
horizontal, vertical, end-fed, or other) are easier to tune with these
other styles, but the style offered in the link is fairly general
purpose.

Old AM (tube) radio parts are perfect for building your own tuner.

It seems I need to find some

It may not be easy, but if you can find the right shop, you will find
many. Tell the shop owner you want this for experimentation and you
might get something that isn't in the shop display. The only thing
you really need is the variable capacitor from two radios. This
technology was very common and found in nearly every home in the 1950s
and 60s, but now would be rare unless you find that shop.

Thank you for your patience,

Feel free to ask more questions when it comes time to put this
together.

73's
Richard Clark, KB7QHC