Comcast Corp. shares /zigman2/quotes/209472081/lastsale CMCSA -5.91% are up 1.7% in premarket trading Tuesday after MoffettNathanson analyst Craig Moffett upgraded the stock to buy from neutral and raised his price target to $52 from $49. He wrote that Comcast's stock has dramatically outperformed Charter Communications Inc.'s stock /zigman2/quotes/201656355/lastsale CHTR -3.19% over the past year, with Charter shares up more than 50% while Comcast shares have only added 25%. This partly makes sense to Moffett because there have been concerns about Comcast's legacy media businesses, while Charter is a pure play on cable. "But at Comcast's current valuation, either NBCU, or Sky, is arguably being priced at less than zero," he wrote. "Even with a conglomerate discount, Comcast is too cheap on any reasonable sum-of-the-parts valuation." Moffett continues to have doubts about the prospects for Comcast's cable networks and the Sky business, but he said "the suggestion that NBCU and Sky are worth more than zero seems unlikely to draw much argument." Comcast's stock has lost 4.7% over the past three months, as the S&P 500 /zigman2/quotes/210599714/realtime SPX -3.37% has added 5.9%.