Better use prefetch or fastq-dump download, instead of wget !
Many .sra files are compressed against a reference which is not included in the .sra file.
The SRA-tools prefetch or fastq-dump automatically download both the .sra files and the reference sequences required for decompressing. Additionally it gives download success control.
Download using wget
# get SRA file location on NCBI server (alternatively, search at NCBI website)
# download using wget
# converting SRA file into fastq
many samples will not work using wget, as the compression related reference genome is missing
Solution: use prefetch or fastq-dump, instead of wget
fastq-dump --split-3 SRR649944 (only access number without path Data/SRR649944 or ./SRR649944) will force fastq-dump to download the sample directly from NCBI instead of using the local copy.