A method for sealing a semirigid solid dielectric radio frequency quality coaxial cable against ultrahigh vacuum is described. It was developed for the output cable of a hydrogen maser frequency standard that operates at the single spot frequency of 1420.4 MHz. The cable is squeezed in two places a quarter of a wavelength apart so that the two impedance mismatches introduced cancel to the first order at the spot working frequency. The length of solid dielectric trapped between the two ‘‘tourniquets’’ forms an excellent and enduring vacuum seal.