TRABEM wrote:
"I didn`t price it yet, but I need more technical information!"

There`s a better approach than high "Q" capacitors for a VLF loop. It`s
been available since the year 1912 and much used soon after its
invention.

Edwin H. Armstrong, 1890 - 1964 was radio`s most productive inventor. He
invented regenerative control in 1912. I think he awakened his sister in
the middle of the middle of the night screaming : "Eureka, I`ve found
it!" or something to that effect. It wasn`t ubique for Howard Armstrong
to discover things. Following controlled regeneration, he discovered the
principle of the superhet in 1918, superregeneration in 1922, and the
complete system of frequency modulation in 1933. He would battle RCA and
Sarnoff for his entire life over control of his discoveries. I recall
seeing a photo of the battery portable radio Howard built and gave his
bride as a wedding present on an IEEE magazine cover.

Ever since 1912 there have been regenerative circuits introducing a
fraction of a receiver`s output back into its input to enhance its
amplification and sharpen its selectivity. Some of these are called "Q"
multipliers.

A "Q" multiplier is an oscillator circuit which has its regenerative
feedback adjusted just below the point of oscillation. It amplifies the
signal many times and shrinks the apparent bandwidth the tuned circuit
accepts. I`ve seen them used for reception of WWV at Boulder on 60 kHz
and for other low frequencies. This seems easier than using super parts.
Use some positive controlled feedback in the loop circuit. Adjust it for
convenience.

Best regards, Richard Harrison, KB5WZI