[time-nuts] HP 8568B

Hui Zhang ba6it at 163.com
Sun Jun 29 02:34:25 UTC 2014


Hi Tommy:
     I used each span to do my test, they are also have frequency diffrence, the 42Hz is result of 1kHz span.  I also use marker counter function, sometime I use 'peak serach' function, it will gave me a peak value, very helpful. I am thinking about the reason you and Alex talked about 'internal LO's are locked to the 10 MHz reference', I thought the internal OCXO will not join work if a EXT REF in, am I wrong?
Thanks you!


Hui Zhang








At 2014-06-29 10:24:22, "Tommy phone" <tholmes at woh.rr.com> wrote:
>Hi Hui...
>The first thought is that you are tied to the resolution of the span divided by the number of displayed points -1. Try a narrower span. If you look at the absolute accuracy spec that error may be within the '66's capability.
>
>Also, I believe there is a marker counter function that will give you a more accurate reading.
>Another consideration is that not all of the internal LO's are locked to the 10 MHz reference.
>Don't panic yet :)
>
>
>From Tom Holmes
>
>
>> On Jun 28, 2014, at 9:48 PM, "Hui Zhang" <ba6it at 163.com> 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 fo
> u
>> 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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