Attenuation measurement system in the frequency range of 10 to 100 MHz

An attenuation measurement system, which employs a traceable inductive voltage divider (IVD) at 1 kHz as a reference standard and dual-channel intermediate frequency (IF) substitution method, is developed as an attenuation standard in the frequency range of 10 to 100 MHz. High isolation between the channels is achieved by introducing an assembly of light emitting diode, optical fiber, and photodetector into the system. Sources of uncertainties of the system, such as leakage, are discussed and the expanded uncertainties are expected to be 0.001 dB for an attenuation range up to 20 dB and 0.04 dB for 80 dB.

I. Introduction

In RF and microwave attenuation measurements and standards, the intermediate frequency (IF) substitution method has been widely used. Usually, the frequency at or near 30 MHz is selected as an IF and the waveguide below-cutoff (WBCO) attenuator is employed as a reference standard [1]– [3]. However, for measurements in the frequency range below 100 MHz, it is difficult to use this method directly, since the frequencies of the RF signal and the IF signal are very close. An alternative technique is to use an inductive voltage divider (IVD) as a reference standard, which is operated at audio frequencies such as 1 kHz, 10 kHz [4], [5], and 50 kHz [6].