A probe head for nuclear magnetic resonance measurements is disclosed in
which at least a first kind of nuclei with a first, higher resonance
frequency and a second kind of nuclei with a second, lower resonance
frequency are excited within a magnetic field. The probe head comprises a
first input/output terminal for the higher resonance frequency and a
second input/output terminal for the lower resonance frequency. A
measuring coil cooperates with a sample. The measuring coil has a first
terminal end and a second terminal end. The first terminal end is coupled
to the first input/output terminal and the second terminal end is coupled
to the second input/output terminal. A stop circuit tuned to signals of
the higher resonance frequency is arranged between the second terminal
end and the second input/output terminal. The stop circuit, further,
comprises a line having a length equalling a quarter wave length of the
higher resonance frequency. The first line is arranged in series with the
measuring coil.
