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" <alex...@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
> 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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>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
>73
>KJ6UHN
>Alex
>
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