According to Radio-Locator.com, neither station uses a directional antenna. They are both at typical Class B power, both on 104.1 MHz. According to Bing.com, the distance between Harrisburg and Allentown is 87 miles.
Nearby is another short-spaced pair of FM stations. WQXA York and WJZ-FM Catonsville-Baltimore. Both are on 105.7 MHz, both have typical Class B power, and are only 53 miles apart. But at least each of these stations uses a directional antenna.