[time-nuts] HP 8568B

[Hui Zhang]

Hello:
    I am afraid I made a dumb mistake, I ignored a calibration procedure in the page 3 of manual, it's too front in the book so I missed it, I am very sorry. 
    The procedure is:
    1, Connect CAL OUTPUT to SIGNAL INPUT 2.
    2,Press [INSTR PRESET], [RECALL], [9] on the analyzer.
    3,Adjust FREQ ZERO for a maximum amplitude trace.
    4,Press [INSTR PRESET].
    By follow these step, I adjust the curve peak in the center of horizontal axis, and then I use my 10MHz REF and test other 10MHz source, the normal marker read is 10.000001Mhz - only 1Hz error. It's very good result.
I think it a basic calibration procedure, but I never did it before, it's my dumb mistake. Before I do these adjustment, I almost ready to pull down the 10811 OCXO to make some separate calibration and test work. But it seems unnecessary if I only use EXT REF. But I still decide do some calibration work of that 18011 OCXO at late times.
    At last I'd say many thanks for this group, and every kindly people who trying to help me, thank you!


Hui Zhang
     








At 2014-06-29 10:30:20, "John Miles" <john at miles.io> wrote:
>Are you using the normal marker or the frequency counter marker?  The
>counter marker should be accurate, while the frequency displayed for the
>normal marker position will not be.  You may be able to improve the normal
>marker's accuracy in narrow spans if you run the shift-W self-calibration
>routine but it will never be as good as the counter.
>
>-- john, KE5FX
>
>> -----Original Message-----
>> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
>> Behalf Of Hui Zhang
>> Sent: Saturday, June 28, 2014 6:49 PM
>> To: Discussion of precise time and frequency measurement
>> Subject: [time-nuts] HP 8568B
>> 
>> 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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