Urban indoor signal and noise measurements in the Medium Wave Band

This paper presents a comparison study between carrier to noise (C/N) values measured outdoors and indoors in five office buildings of a city in Spain, related to radio broadcasted signals. Measurements were carried out in Bilbao at three frequencies in the medium wave band: 639 kHz, 990 kHz and 1305 kHz. Results show that outdoor mean C/N results are 7.5 dB higher than indoors for 639 kHz and 6.5 dB and 5.9 dB for 990 kHz and 1305 kHz, respectively, with a high spatial variability. These results are mainly due to signal losses when penetrating in buildings, with mean values of 7.5 dB, 8.1 dB and 5.2 dB, respectively. It has also been observed that outdoor noise levels are about 1-3 dB higher than indoors. In some cases noisy spots have been detected where the mean field strength levels are 10 dB higher than outdoors. The measurements provide noise mean field strength levels (both indoors and outdoors) in the range of 65-70 dB¿V/m, values higher than the ones suggested in Rec. ITU-R P.372.