Your NMR experiment need high quality components.
•Passive, narrowband, high insulated duplexer.
•Narrow operating bandwidth, less than 20% of center frequency.
•High quality and robustness.
•Short delivery time.
•Frequency range 1 to 500 MHz.
•Maximum signal power: 250 W.
•50ohms Input / Output Impedance.
•Isolation between Tx and Rx greater than 50 dB.
•SMA, BNC or N connectors.