Most of the OTA TV stations in OKC broadcast on UHF frequencies, but channels 5 (KOCO) and 13 (OETA) broadcast on VHF frequencies instead. Most modern TV antennas perform best with UHF frequencies and don't work well (or at all) with VHF signals. To reliably receive channels 5 and 13, you must have an antenna capable of receiving both VHF and UHF signals.