The effects of broadening of frequency spectra of quasi‐monochromatic very low frequency (VLF) signals were observed in the polar ionosphere when VLF transmitter signals were registered on the satellite "Intercosmos‐19". Broadening of the spectrum was mainly registered on the electric antenna to the extent of Δf ≤ ± 1 kHz. Broadening of the VLF signal and intensive extra low frequency (ELF) noise with f < 1 kHz were observed simultaneously. Such effects can be explained by a transformation of the initial whistler‐wave, into whistler‐mode waves with wave‐normals very near the resonant cone, by small‐scale ionospheric irregularities. These irregularities can be caused by ion‐acoustic or ion‐cyclotron waves. The effect of the broadening of the VLF signal spectrum can be used as a diagnostic of ionospheric turbulence and field‐aligned electric currents in the upper ionosphere.

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