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AGILENT (HP) 8656B 100 kHz RF Signal Generator within acceptable alignment?

Chris Lawrence

Active Member
Jul 9, 2021
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Looking at buying one and viewing ads on eBay. Two of the listings show the unit with a frequency counter or a spectrum analyzer.

What is considered “within tolerance”?

One listing shows the signal is 3,654Hz off.
The other listing says it’s “calibrated” but the spectrum analyzer shows it’s 117Hz off.

Thank you.
 

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some things to consider. frequency accuracy and stability per specs is related to ambient temperature and proper warm up. also is the frequency counter shown accurate? is the spectrum analyzer accurate? is the room really hot/cold? did they just turn it on then show the measurement or did it warm up for the 30 min to an hour to maintain stability? lots of questions that matter. with that being said those rf signal generators are spot on +- a few hertz when fully calibrated and operated under the correct conditions for the most part. what i would suggest is if you are this serious about this type of equipment and its accuracy, you need to get a 10mhz gpsdo. this will keep the whole bench working on an extremely accurate frequency standard which in turn will eliminate the frequency errors in equipment. it is essential for frequency counters, spec analyzers, rf signal generators etc. without it you will be accurate but not spot on. side note: i would consider the spec analyzer one before the frequency counter one, its within tolerance.
 
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"Calibrated" doesn't mean "perfect". The manufacturer of the equipment specifies what the maximum error of their product is, and the calibration lab uses that information, including the temperature, relative humidity, line voltage and several other factors that have to be considered. THEN the "UUT" (Unit Under Test) is compared with the Cal Lab's standard. That's the actual definition of calibration: comparison with a calibrated standard with less maximum error than the UUT.
 
some things to consider. frequency accuracy and stability per specs is related to ambient temperature and proper warm up. also is the frequency counter shown accurate? is the spectrum analyzer accurate? is the room really hot/cold? did they just turn it on then show the measurement or did it warm up for the 30 min to an hour to maintain stability? lots of questions that matter. with that being said those rf signal generators are spot on +- a few hertz when fully calibrated and operated under the correct conditions for the most part. what i would suggest is if you are this serious about this type of equipment and its accuracy, you need to get a 10mhz gpsdo. this will keep the whole bench working on an extremely accurate frequency standard which in turn will eliminate the frequency errors in equipment. it is essential for frequency counters, spec analyzers, rf signal generators etc. without it you will be accurate but not spot on. side note: i would consider the spec analyzer one before the frequency counter one, its within tolerance.
Thanks, Groundwire. That’s good info. I think my question is more along the line of, “What is considered a reasonable tolerance for one of these units?”. Assuming warm up and alignment of the other test equipment is spot on, 3k seems drastic. I’m also thinking in terms of its main use of tuning the rx of radios.

I do have a 10MHz reference and distribution amp for it.

Appreciate the help.
 
Thanks, Groundwire. That’s good info. I think my question is more along the line of, “What is considered a reasonable tolerance for one of these units?”. Assuming warm up and alignment of the other test equipment is spot on, 3k seems drastic. I’m also thinking in terms of its main use of tuning the rx of radios.

I do have a 10MHz reference and distribution amp for it.

Appreciate the help.
yes 3k is alot. the manual is available onlie for free as a pdf so it should have the specs in it. go for the one that is a few hz off, your 10mhz reference will bring it spot on.
 
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