Income investors often set a minimum dividend yield as a requirement for their buy decisions. That eliminates a number of stocks from consideration. This requirement could also increase market risk since it tends to limit investments to just a few sectors.

A diversified portfolio should hold more than large drug companies and big-name tech stocks that are no longer growing rapidly but are paying large dividends. Covered calls can increase the number of stocks that income investors can select from and help them diversify their portfolio without sacrificing income.

A covered-call strategy involves selling call options on a stock you own. Selling calls generates instant income known as a premium.

A covered call allows you to participate in the upside of the stock, while the income will help offset any downside. This is an excellent strategy for income investors to consider, and I want to use an example of a trade I like right now to illustrate the amount of income that is possible.

Arkansas Best (Nasdaq: ABFS) is a trucking company that has been around since 1935. It operates about 3,700 tractors and 20,000 trailers in long-haul and local pickup delivery operations. Arkansas Best also provides logistics support to its customers, using its IT systems to help companies manage inventory and schedule deliveries and pickups. Additionally, it leverages its internal processes and infrastructure to provide emergency roadside assistance to other trucking companies.

Revenue grew 25% last year and 45% in the first quarter of 2013. For the full year, analysts expect 9.4% revenue growth.

The company is stable but has been unprofitable for several years. Analysts expect a return to profitability this year with earnings per share (EPS) of $0.21 and a significant jump in profits to $1.70 a share in 2014. If they are right, now would be an ideal time to invest in ABFS.

Income investors, however, might not like the low dividend of $0.12 a year, a yield of just 0.4%. But the company has demonstrated its commitment to rewarding shareholders