[time-nuts] Fw: HP 5065A performance vs. others

Corby Dawson cdelect at juno.com
Mon Mar 22 17:10:49 UTC 2010


 
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
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