SoftBank Group increased its stake in Sprint Corp. a second time this month, acquiring ¥7.51 billion($73 million) of stock in the unprofitable U.S. wireless operator.

The Japanese carrier paid for 16.8 million shares, according to Bloomberg calculations based on a SoftBank filing with the U.S. Securities & Exchange Commission. The latest purchase follows an earlier ¥10.86 billion ($87 million) investment in Sprint that the Tokyo-based company announced Aug. 13.

SoftBank's billionaire founder Masayoshi Son has reiterated his commitment to Sprint as it shows signs of recovery after recording its third consecutive gain in subscribers. Son has said he already sees "light at the end of the tunnel" for the carrier, which booked losses in six out of the past seven quarters, but the turnaround may take two years.