A radio spectroscopic driftscan survey in the 21cm line with the Nançay Radio Telescope of 0.08 steradians of sky in the direction of the constellation Canes Venatici covering a heliocentric velocity range of -350 < V _ { hel } < 2350 km s ^ { -1 } produced 53 spectral features , which was further reduced to a sample of 33 reliably detected galaxies by extensive follow-up observations .
With a typical noise level of rms = 10 mJy after Hanning smoothing , the survey is – depending on where the detections are located with regard to the center of the beam – sensitive to M _ { HI } = 1 - 2 { \times } 10 ^ { 8 } h ^ { -2 } { M } _ { \odot } at 23 h ^ { -1 } Mpc and to M _ { HI } = 4 - 8 { \times } 10 ^ { 7 } h ^ { -2 } { M } _ { \odot } throughout the CVn Groups .

The survey region had been previously examined on deep optical plates by Binggeli et al .
( 1990 ) and contains loose groups with many gas-rich galaxies as well as voids .
No galaxies that had not been previously identified in these deep optical surveys were uncovered in our H i survey , neither in the groups nor the voids .
The implication is that no substantial quantity of neutral hydrogen contained in gas-rich galaxies has been missed in these well-studied groups .
All late-type members of our sample are listed in the Fisher and Tully ( 1981b ) optically selected sample of nearby late-type galaxies ; the only system not contained in Fisher and Tullys ’ Catalog is the S0 galaxy NGC 4203 .
Within the well–sampled CVn group volume with distances corrected for flow motions , the H i mass function is best fitted with the Zwaan et al .
( 1997 ) H i mass function ( \alpha = -1.2 ) scaled by a factor of f=4.5 in account of the locally overdense region .