The 11-day old blackout of CBS on Time Warner Cable systems seems to be having a minimal effect on the network’s ratings.

Last week, the first full week of blocked service for more than three million Time Warner customers, the network topped its competitors in total viewers and in all the ratings categories important to advertisers.

One reason perhaps: RadioShack reported Monday a “double-digit” increase in sales of high-definition antennas in the three big cities being blacked out — New York, Los Angeles and Dallas. (The company provided no specific numbers.)

Time Warner Cable has been suggesting that customers try watching CBS the old-fashioned way – on a broadcast signal to an antenna — since it removed the network from its cable systems on Aug. 2 in a dispute over what are known as retransmission fees.