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We present the results of multi-longitude observations of KV Cancri, an RRLyrae star showing an irregular Blazhko effect. With a pulsation period of0.50208 day, the times of light curve maxima are delayed by 6 minutes per day.This daily delay regularly leads to long periods of time without maximum lightcurve observations for a given site. To cope with this observing time windowproblem, we have organized a multi-longitude observation campaign including atelescope of the AAVSONet. From the observed light curves, 92 pulsation maximahave been measured covering about six Blazhko periods. The Fourier analysis ofmagnitudes at maximum light has revealed a main Blazhko period of 77.6 days andalso a secondary period of 40.5 days. A Fourier analysis of (O-C) values didnot show the secondary Blazhko period. The frequency spectrum of the completelight curve, from a Fourier analysis and successive pre-whitening withPERIOD04, has shown triplet structures around the two Blazhko modulationfrequencies but with slightly different periods (77.8 and 42.4 days). Thesecond Blazhko frequency is statistically not a harmonic of the main Blazhkofrequency. Besides the two Blazhko modulations KV Cnc presents otherparticularities like irregularities from Blazhko cycle to cycle and very fastmagnitude variations which can reach a maximum of 2.5 magnitudes per hour overa period of 15 minutes. This campaign shows that regular observations byamateur astronomers remain important. Indeed such a detailed characterizationof the Blazhko effect could not be obtained from large-scale surveys, ascooperative long time-series observations are needed.

Multi-Longitude Observation Campaign of KV Cancri: an RR Lyrae star with irregular Blazhko modulations