Drug Fair Inc. earned $268,880 (16 cents a share) during its second quarter ended July 26 compared with a loss of $413,043 a year earlier, acccording to unaudited data released by the company yesterday. Sales increased 10.8 percent to $72.2 million from $65.1 million during the same three months in 1979.

In general, Drug Fair's quarterly earnings appeared blostered by the discontinuance earlier this year of the company's Wrangler Ranches and most of its Soup'r Scoops sandwich and ice cream stores.

Pretex income from continuing operations of $526,118 compared with a loss of $449,668 for the same quarter in 1979.

Sales and net income for the six months ended July 26 also improved, with net income of $568,130 (34 cents) compared with a loss of $40,952 a year earlier. Sales increased from $127.8 million to $139.6 million. Radiation Systems Inc. of Sterling, which manufactures communications antenna products, reported record sales for the fiscal year ended June 30 of $7.6 million, up 35 percent from $5.6 million the previous year. Earnings were $836,000 ($1.06 a share) compared with $666,000 (88 cents) a year earlier. w

Fourth-quarter net income was $262,000 (33 cents) on $3.1 million in sales compared with net income in the previous fourth quarter of $157,000 (19 cents) on $1.9 million in sales.s.