[time-nuts] HP 8568B

John Miles john at miles.io
Sat Jun 28 22:30:20 EDT 2014

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
> 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
> I use it measure a nother GPSDO (Trimble ThunderBolt locked to GPS), it
> have 42Hz diffrence. I am very sure both of my two GPSDO is good, if I use
> HP53132A counter to compare them they will has less 1E-10 (1mHz)
> 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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