A supplemental device for mounting on a rod-type antenna, particularly the antenna of a mobile C-B installation, for reducing the overall noise level in connection with the operation of the squelch control, utilizing a pair of assemblies each having at least one ring member and a plurality of cooperable radially extending rod members symmetrically arranged and intersecting the axis of the associated ring member, with such ring and rod members secured in rigid relation and lying substantially in a common plane, such assemblies being disposed in spaced parallel planes and rigidly connected substantially on their common axis by a cross member having means cooperable therewith for adjustably securing the device to an antenna, whereby it may be secured thereto at an optimum location therealong, with such antenna extending thereat in a plane parallel to said first mentioned planes.