[time-nuts] HP 8568B

Alex Pummer alex at pcscons.com
Sun Jun 29 13:29:00 EDT 2014



On 6/29/2014 8:33 AM, Hui Zhang wrote:
> 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
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> 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
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-
>>> nuts
>>> and follow the instructions there.
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I have to deeply disappoint you; you are not the first one who did not 
follow the manual,!
73
Alex


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