  We describe a fully ultra-high vacuum compatible scanning tunneling
microscope (STM) optimized for radio-frequency signals. It includes in-situ
exchangeable tips adapted to high frequency cabling and a standard sample
holder, which offer access to the whole range of samples typically investigated
by STM. We demonstrate a time resolution of 120 ps using the nonlinear
I(V)-characteristic of the surface of highly oriented pyrolithic graphite. We
provide atomically resolved images in pulse mode related to a spatially varying
nonlinearity of the local density of states of the sample, thus, demonstrating
the possible spatial resolution of the instrument in pulse mode. Analysis of
the noise reveals that changes in the tunneling junction of 50 pA are
dynamically detectable at 120 ps time resolution.
