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" <thol...@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" <ba...@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 f
o
> 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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