This instrument has been designed for production lines and research on wide band amplifiers such as those used in television and frequency modulation receivers. Its outstanding performance is due to the incorporation of original ideas specially adapted to this new technique. In particular the range 5 - 220 Mc/s is covered on a single scale without switching. All I.F. stages can therefore be aligned, whatever may be their working frequencies, and so can R.F. and local oscillator stages up to and including 220 Mc/s. This very wide frequency range is obtained by using the difference in frequency between two oscillators ,one being swept about a fixed frequency and the other being unmodulated but variable. Both frequencies are always higher than 220 Mc/s. A great advantage of this system is that only the wanted frequency can act on the circuit under test, all other frequencies being higher.This result is not possible if the sum of the internal oscillator frequencies is used. Other features are: Frequency sweeping is obtained by a system of variable permeability. Neither mechanical parts nor electronic tubes are used, this leading to stability and linearity. The high attenuable output allows the use of any oscilloscope provided with a horizontal amplifier, even if the oscilloscope is not very sensitive or the receiver out of alignment.