Hello all,
I have a little problem with my old, but very reliable HP 8591A spectrum analyzer.
On the narrow spans i have a little center frequency variation, at higher spans it no longer falls on.
Example:
300 MHz -20 dBm cal out signal
Res Bw 3 KHZ
VBW 3 KHZ
Span 200 KHz
Marker counter resolution 10 Hz
Read frequency deviation is about 299.99978 and 300.00017 MHz
The frequency is unconditional stable with frequency counter on the cal output.
I have read that the problem may sit in the A25 counterlock assy.
I do not have an clip manual from the unit.
Is there somebody who has a solution for this problem or maybe the counterlock assy manual (if this is the problem board?)
Despite everything i only want a HP/Agilent spectrum analyzer ;-)
Regards,
Hifreak
Edited by: Hifreak on Apr 3, 2014 2:48 PM
Edited by: Hifreak on Apr 3, 2014 2:49 PM
I have a little problem with my old, but very reliable HP 8591A spectrum analyzer.
On the narrow spans i have a little center frequency variation, at higher spans it no longer falls on.
Example:
300 MHz -20 dBm cal out signal
Res Bw 3 KHZ
VBW 3 KHZ
Span 200 KHz
Marker counter resolution 10 Hz
Read frequency deviation is about 299.99978 and 300.00017 MHz
The frequency is unconditional stable with frequency counter on the cal output.
I have read that the problem may sit in the A25 counterlock assy.
I do not have an clip manual from the unit.
Is there somebody who has a solution for this problem or maybe the counterlock assy manual (if this is the problem board?)
Despite everything i only want a HP/Agilent spectrum analyzer ;-)
Regards,
Hifreak
Edited by: Hifreak on Apr 3, 2014 2:48 PM
Edited by: Hifreak on Apr 3, 2014 2:49 PM
I don't think you really have a problem, if you don't have any error messages then I think your analyzer is working as it's supposed to. A spectrum analyzer is not the best instrument for measuring a frequency with high accuracy, (and especially not with a frequency span of 200kHz). You didn't mention in your posting if you have locked the spectrum analyzer frequency to any source of high stable 10MHz signal or similar. Original this type of spectrum analyzer depend on a quartz crystal and the frequency can differ slightly. This depends on the temperature of the crystal etc. I don't have any CLIP for the 8591 but often HP have used 100MHz crystals or crystal oscillators. To be sure about your measurement you should let the instrument to heat up at least 30 minutes. Also there is a frequency calibration that should be done, you'll find it in the CAL menu. (I assume that you are familiar about this but wanted to mention it to be sure.)
All frequencies read on the display will be measured in comparison to the 300MHz reference signal. If your reference signal is not right, then your measurements will also be wrong. Still a spectrum analyzer of this type is best for measuring levels not exact frequencies. If your analyzer has an input of 10MHz reference and you have a stable source, as a GPS receiver or similar, you will get more consistant results from day to day.
You mention a frequency counter. This instrument can have the same "problem" and you can't be sure what instrument show the right frequency if you haven't locked it to a stable reference. There are types of HP analyzers with crystal ovens and these are better, but there can still be differences. Measuring frequencies "exactly" can be tricky...
As a comparison my HP8563E and HP5350B (counter) are both locked to GPS. If I measure the reference I will of course get 300.000000MHz. The reference from my other analyzer, (a HP8594 with free running oven controled oscillator), the counter is 11Hz wrong. With the HP8563E in 200Hz span and RBW=VBW=3Hz I get the same counted result.
I don't think the 8591 can go this narrow and then you will not be able to measure with high accuracy.
Enjoy your 8591, it's still a very good instrument!
Regards
Jens