Responses of radio interference measuring apparatus employing an envelope quasi‐peak detector

Abstract In conventional radio interference measuring apparatus, the direct‐QP detection method is used. In this method, intermediate frequency output is added directly to a quasi‐peak detector to obtain an output corresponding to the quasi‐peak level of the interference. However, a new type of QP detection method has recently been used in the radio interference measuring apparatus as demonstrated in the spectrum analyzer with the quasi‐peak detection capability. In this method, the intermediate frequency output is first added to an envelope detector and then to quasi‐peak detector. But it is not yet known if this measuring apparatus with its combination of detector, the envelope‐QP detector, satisfies all standards, including present CISPR specifications. The latter is determined based on the response characteristics of the direct‐QP detector system. In this paper, theoretical computer comparison has been made between the direct‐QP detector system and the envelope‐QP detector system to study responses to Gaussian noise and the repeated pulse input. It is found that the measuring apparatus with an envelope QP detector does not easily satisfy the present CISPR specifications. To improve the response characteristics of this new apparatus having the envelope‐QP detector, guidelines, have been indicated for the bandwidth and the charge and discharge time constants.