The 501-27555-81 from Wenzel Associates is a OCXO with Frequency 100 MHz, Supply Voltage 15 V, Phase Noise -130 dBm/Hz@100 Hz to -100 dBm/Hz@10 Hz, Phase Noise 1 kHz -158 dBm/Hz, Phase Noise 10 kHz -176 dBm/Hz. Tags: Module with Connectors, OCXO. More details for 501-27555-81 can be seen below.