The Model 2002A covers the 1 to 2500 MHz range in three bands. Band 1 is covered by a 1 to 500 MHz heterodyne sweep oscillator. Band 2 is covered by two fundamental oscillators which sweep from 500 to 1000 MHz and 1000 to 1500 MHz, respectively. Band 3 is covered by a single fundamental oscillator sweeping from 1500 to 2500 MHz. Additionally, ail four oscillators may be stacked {sequentially swept) to cover the entire 1 to 2500 MHz instrument range {band 4). Each of the four frequency bands {1-500 MHz, 500-1500 MHz, 1500-2500 MHz, and 1-2500 MHz) may be used in three modes of operation: start/stop, Af, or CW. It can be swept over any portion of a given band, in either direction, at any rate from 50 sweeps per second to 1 sweep every 100 seconds. Manual, triggered, or recurring sweeps are provided. The sweep frequency, sweep width, and output attenuation may be controlled by external voltages. Other features of the Model 2002A include a SLOPE control which compensates for frequency dependent variations in the external circuitry, and a 1 kHz square-wave modulator for low-level recovery applications. This instrument also includes an elaborate frequency marker system. Up to five crystal-controlled birdy marker modules {single frequency or harmonic type) may be plugged into the Mode! 2002A. Each module has its own front-panel on/off switch. Additionally, a single module producing harmonic markers at 1, 10, 50, and 100 MHz intervals may be installed. Front-panel SIZE and WIDTH controls enable optimum adjustment of the marker display. The marker system features dual-amplitude markers for easy identification. In application, the markers may be tilted up to 90° for easy viewing when displayed with steep transition signals, or they may be rectified by a front-panel switch for X-Y plotter applications. Other optional features include a rear-panel Auxilliary RF Output and a Pen Lift circuit for use with X-Y plotters. Most optional features, as well as the functional circuits for the basic sweep generator, have modular plug-in construction. This allows optional features to be factory installed at the time of purchase, or customer installed at a later date. This concept offers protection against obsolesence, since updated and additional features can be simply and economically added as new test procedures dictate. In addition, maintenance problems can be greatly simplified by stocking several modules instead of hundreds of discrete components.