The 501-25558a from Quantic Wenzel (Wenzel Associates, Inc.) is a OCXO with Frequency 20 MHz, Supply Voltage 15 V, Phase Noise -153 dBm/Hz@100 Hz to -128 dBm/Hz@10 Hz, Phase Noise 1 kHz -165 dBm/Hz, Phase Noise 10 kHz -168 dBm/Hz. Tags: Module with Connectors, Low G-Sensitivity. More details for 501-25558a can be seen below.