Cut meat into strips a little less than 1/4-inch thick. Place strips in a shallow bowl. Combine salt, pepper, garlic powder, and onion powder in a small bowl. Rub spice mixture into strips. Cover loosely with plastic wrap, and marinate for 48 hours in the refrigerator. Remove a rack from the oven. Preheat the oven to 115 degrees. Remove the strips from the marinade and lay them directly on the oven rack so that air can circulate around them. Line the bottom of the oven with aluminum foil to catch the drippings. Place the rack in the oven, leaving it partially open to maintain a constant temperature of 110 to 115 degrees. Leave the jerky in the oven until well dried, 6 to 8 hours.
Note: The USDA recommends cooking the beef jerky at 160 degrees for the first 4 hours and then reducing the temperature to 130 degrees during the dehydrating process.