Charly wrote:
In fact wiring is totaly different, but the question remains anyway :
what will be the best desing between
http://www.m0ukd.com/Magnetic_Long_Wire_UnUn/index.php
and
http://www.hard-core-dx.com/nordicdx.../9_1balun.html


There a lots of designs for 9:1 transformers, some work better than others,
and in practice none works better than all of the others all of the time.

You don't need a toroid, although they have become popular these days, a
ferrite rod will do too. You can buy them on eBay from various Warsaw pact
countries, where they were obtained from Russia. The price depends more on
the quantity and postage method than anything else.

If you look at the transformer, the simplest method of connecting it is to
connect the antenna to the primary and the recevier to the secondary.

9:1 transformers are usually used for random wires with the other end of the
antenna being a ground rod. This is good for electricaly safety because the
transformer appears as close to zero resistance to static and lightening,
making it a long wire connected to ground.

At RF frequencies the transformer is not a direct short and the signals
go across it to the receiver.

The other end is connected to the receiver and eventually connected to ground.
Many places (e.g. the US) require the coax to be grounded (and that ground
bonded to the electrical system ground) where it enters the house.

Whether or not grounding the antenna end of the receiver coax will improve
things or not is questionable. In some cases it does, in others it does
nothing and in even different cases it makes things worse.

In any case, the best way to mount a transformer in a plastic box is so that
the bottom is empty and a small hole is drilled in it to allow moisture to
exit. Eventually humidity or even water gets in and the drain will help.

Note that there is no recent research on the use of these devices. There is
an article that has been referenced here several times. It was written 14
years ago, and commented that the need for a 9:1 transformer was lessend
(and maybe eliminated) by a modern receiver.

The author did mention that it was needed for a "Sky Buddy", but I'm not
sure there were many of them in use then or now.

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.