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 fou
nd any infomation about how to do it. What do I do now? Anyone give me a
suggestion? Any infomation will be appreciate.
Hui Zhang
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