Resistance Comparison at 3 300 Mc/s by a Novel Method

The u.h.f. resistance of specimens of wire form is deduced from changes in Q of ¿-¿ concentric-line resonator in which the specimen forms a ¿-¿ section of the inner conductor. The apparatus is calibrated with copper and molybdenum specimens of calculated u.h.f. resistance ratio. Q measurements are made by a novel method in which the resonator is compared with a standard one. Both resonators are coupled to a frequency-modulated oscillator and the difference in output of crystal detectors in the two resonators is displayed on a cathode-ray tube against the frequency-modulating voltage. A null indication is obtained when a triple balance is secured, (a) of resonant frequencies (b) of Q´s and (c) of peak heights of the resonance curves. The load added to one of the resonators to effect the Q balance is removed and the increase in peak output from its detector gives the (square of) the ratio of the unloaded Q´s. Results are given for the effect of different surface treatments on solid copper, for different thicknesses of copper plating on steel, and for similar plated layers fused on the steel in hydrogen. These results are discussed and shown to agree with theory and expectation.