Some design features exclusive to the HP 5065A might help explain the extra performance. 1- The 5065A is the only one I know of that actively regulates the C-field current. The others just have a precision voltage source that feeds the C-field thru a resistance array. 2- The reference cell in the 5065A is the only one that has a TED (thermoelectric device) to control the density of the vapor in the cell. (to high or low a level and the S/N ratio starts to suffer.) 3- The 5065A cell is fairly long, especially compared to the most modern cells. The S/N ratio of the RX signal is directly related to the cell length. The RX S/N spec. of the 5065A is >250. The best I have tested so far and probably the all time record holder was >4000! You can see a variety of cells @ http://www.leapsecond.com/pages/rb-cells/ 4- The RX cavity is triple shielded by cylindrical shields. Some of the older units, V4700, 304D, etc., also were triple shielded. 5- The multiplier (A3) and synthesizer (A1) as per the excellent HP design philosophy of the time probably also have a marked contribution to the performance. I have in the past driven an HP 5065A RX with a gutted FRSC electronics system ( I called it the 5065Jr.). Needless to say the performance suffered. Corby Dawson ____________________________________________________________ Diet Help Cheap Diet Help Tips. Click here. http://thirdpartyoffers.juno.com/TGL2141/c?cp=PQJBUaYcIp0Mym_67CB48QAAJ1ABLZFyqoH-WnHH1GJ345whAAYAAAAAAAAAAAAAAAAAAADNAAAAAAAAAAAAAAAAAAAYQAAAAAA=
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