[time-nuts] HP 8568B

[Hui Zhang]

Hello all:
    Rencently I bought a second-hand HP8568B Spectrum Analyzer, it kind of vintage but works well. Only problem is its time base lost accurate. When I use it measured my HP Z3801A output (locked to GPS), the center frequency read is 9.999912MHz, about 88Hz diffrence. So I decide to use  my Z3801A for its external reference. When I connected the cable and set the reference switch in rear paneal to EXT, the CRT displayed "EXT REF", I believed it worked. But when I use it measure a nother GPSDO (Trimble ThunderBolt locked to GPS), it still have 42Hz diffrence. I am very sure both of my two GPSDO is good, if I use my HP53132A counter to compare them they will has less 1E-10 (1mHz) diffrence. And then I tie a BNC three-way connect from my Z3801A, one way to 8568B's EXT stand input, one way to the signal input in front panel, the  diffrence is still 42Hz - it's 10.000042MHz. I was fully confused, do I need a calibration after I used external 10Mhz stand? I read the manual again but not found any infomation about how to do it. What do I do now? Anyone give me a suggestion? Any infomation will be appreciate.


Hui Zhang