RadioShack shares fell 21% in premarket trading after the electronics retailer reported larger than expected quarterly losses. RadioShack posted a net loss of $98.3 million, or $.097 a share, compared to the $0.52 loss per share analysts were expecting. Revenue was down 13% from a year ago to $736.7 million and on a same store basis, sales fell 14%. The company blames the poor sales on a decline in traffic and poor sales in its mobile business.