The SW 503 is a TM 500-Series plug-in that provides a swept frequency of 1 MHz to 400 MHz with variable sweep rate, width, and output level. Crystal-controlled harmonic oscillators provide comb markers with 1 MHz, 10 MHz, or 50 MHz separation. When used with a DC 502 Option 7 Digital Counter, a frequency markerdot can be positioned anywhere within the frequency range of the SW 503 generator, and the frequency of the marker can be read directly on the counter. In the Manual sweep and CW modes, the continuous wave output of the generator can be read to the counter accuracy. Access jacks on the front panel permit external signals to control or modulate the output amplitude and frequency, and to initiate a sweep. The SW 503 has a 50 Ω output impedance; the SW 503 Option 1 has a 75 Ω output impedance.