Measurement Techniques
Volume 3, Number 11, 976-979, DOI: 10.1007/BF00977527

High and Ultrahigh Frequency Measurements

Nonlinearity of cutoff attenuators due to the effect of loading

L. A. Birger

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Abstract

1.  The nonlinearity of a cutoff attenuator due to the loading effect is determined by the initial attenuator loss and depends to a great extent on the relation between the reactive and resistive components of the load and source impedances.
2.  In wide-band cutoff attenuators the value of the load impedance reactive component is bound to be substantial. For such attenuators nonlinearity decreases proportionately to a decreasing field strength when the initial loss is increased. In order to attain a nonlinearity of |Delta|le0.1 db it is necessary to have an initial loss of A0ge40 db, and for |Delta|le0.01 db the loss should be A0ge60 db.
3.  For attenuators working at a fixed frequency (for instance, intermediate frequency attenuators used in superheterodyne circuits for measuring attenuation), it is possible to reduce nonlinearity by a very precise tuning to resonance of the circuits connected to the exciting and receiving electrodes. In such attenuators nonlinearity decreases proportionately to the square of the output voltage when the initial loss is increased. In order to attain a nonlinearity of |Deltale0.01 db it is necessary to have an initial loss of A0ge26 db.
4.  The nonlinearity due to loading is considerable, and in many cases may predominate over the nonlinearity due to spurious types of waves.

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