Hi Mike:
A lot depends on what you are going to be doing.
For example a few decades ago I built an automated system to measure mixer spurs where the frequency of the spurs was
known because I had control of the LO and RF frequency.
IF = +/-LO*n +/-RF*m
The first attempt used the HP 8350B sweeper for the LO and RF sources, but the phase noise was huge so that when you
looked at the IF on the spectrum analyzer the amplitude was jumping up and down many dB. Switched to synthesized signal
generators and that problem went away. Note that the instrument with the best LO was the source for the external
reference inputs for the other two instruments so that they all agreed on the frequency.
http://www.prc68.com/I/RASS_PP.html#Spur
PS A trick to save time is to set the start and stop frequencies so that the IF is just past the start frequency rather
than being centered. That way you can stop the sweep a little after the IF frequency cutting the sweep time by more
than a factor of 10.
PPS First generation spectrum analyzers use analog processing and so the resolution bandwidth is directly tied to the
sweep speed. A digital IF overcomes this limitation (is much faster) and also allows measuring noise power (I^2 + Q^2)
where the analog SA used peak detection. Also a digital IF allows for 1 Hz real RBW which in turns makes for fantastic
sensitivity. You can wrap a wire around a radio and see it's LO frequency. The HP/Agilent 4395A is such a digital IF SA.
http://www.prc68.com/I/4395A.shtml
Example of measuring LO frequency with the 4395A and a good 10 MHz external
reference.
http://www.prc68.com/I/BlkBox.shtml
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.
-------- Original Message --------
Hi,
I have another question about test equipment. When using a spectrum analyzer
to examine the output of a frequency standard, what are the minimum
specification needed? Bandwidth, resolution, sensitivity, etc?
Looking at spectrum analyzers on eBay, I see quite a bit of difference between
various models. Some have a resolution of 10Hz but others are 30Hz or even
100Hz. Some have a minimum frequency of 0.01Hz, 100Hz or even in the kHz
range. Some are only sensitive to 60dBm, but others over 100dBm.
Are any of the cheaper USB spectrum analyzers worth getting?
Most of these are appallingly expensive, so knowing what is needed can
certainly help guide a purchase or to minimize cost. And if a "deal" is found,
knowing that it is or is not adequate can help.
Clearly, better specifications are preferable, but I'm also sure that the
intended application makes a large difference. What is needed for examining a
10Mhz frequency standard might be remarkably different from what is needed for
high-frequency RF work.
Mike
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