1 INTRODUCTION  
2 SAMPLE  
2.1 BAL sample  
2.2 Non-BAL sample  
2.3 Flux variability  
3 OBSERVATIONS AND DATA REDUCTION  
3.1 New 322-MHz observation  
3.2 Archival data  
4 RESULTS  
4.1 Flux measurement and spectral indices  
4.2 Spectral classification  
4.3 Comparison of the spectral class composition between the BAL and non-BAL samples  
4.4 Comparison of the spectral properties between the BAL and non-BAL samples  
5 DISCUSSION  
6 CONCLUSIONS