Toni wrote:
"Yes, but my main objective for all this is feeding the receiver with a
signal coming from the antenna well above te roof and (try to) avoid
feeding the noise picked by the feedline on its way down."

OK. Coax is almost impenetrable at HF. But a directly connected antenna
can accept signal from the coax ecterior unless a balun is used at the
antenna end of the coax.

I recall using a General Electric "V-Doublet" receiving antenna kit in
1938 that used twisted pair for the transmission line. Broadband
transformers were used at each end of the transmission line. They were
interchangeable. The high impedance of the antenna and receiver were
matched to about 100-ohms, the approximate impedance of the twisted
pair.

It worked well on all bands for the multiband GE receiver. The
"V-Doublet" antenna system ignored interference to its transmission
line.

Coax could be used to replace the twisted pair as the primary and
secondary of the transformers are separate and isolated.

Best regards, Richard Harrison, KB5WZI