[time-nuts] HP 8568B
kb8tq at n1k.org
Sat Jun 28 22:54:30 EDT 2014
With some of the HP gear the 10811 is “dead” when you use the external reference. With most of the gear, the 10811 is locked to the external reference. It sounds like your device is in the second category. It locks the 10811, so you need to adjust the 10811 to be close to correct in order for it to lock up.
Even if that’s not the case, adjusting the 10811 to be on / near correct will not hurt anything. It’s worth the effort to get it on frequency.
On Jun 28, 2014, at 10:25 PM, Hui Zhang <ba6it at 163.com> wrote:
> Hello Alex:
> Thanks for you quickly reply, yes I use same source as EXT reference and input signal, it also has 42Hz error. Do you mean even I use EXT reference the intenal 10Mhz time base still need work? If so, I really need calibrate and readjusted it (HP 10811).
> Hui Zhang
> At 2014-06-29 10:17:22, "Alexander Pummer" <alexpcs at ieee.org> wrote:
>> On 6/28/2014 6:48 PM, Hui Zhang wrote:
>>> 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
>>> 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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>> it could happen that thes ystem reports the external reference but the
>> time base reference oscillator doe not lock to it. To check that use
>> the same source fo the reference and also for he input and set the span
>> small few kHz the resolution 1/10 of the span and if you still see the
>> freq error than the spectrum analyzer internal time base 10MHz need to
>> readjusted since it cannot lock to the external reference, that is
>> normal aging that instrument may be 25 years old
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