Hi Jim:
Do you know how the HP/Agilent 4395A stacks up as a SA? I really like
the true RMS power detection and the 1 Hz RBW (not video).
<http://www.home.agilent.com/agilent/product.jspx?id=1000000864:epsg:pro&pageMode=OV&pid=1000000864:epsg:pro&lc=eng&ct=PRODUCT&cc=US&pselect=SR.PM-Search%20Results.Overview>
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.End2PartyGovernment.com/
Jim Lux wrote:
On 9/23/11 10:04 AM, Jose Camara wrote:
I think you are right, often the internal, free running osc will give
you better results. You can use the GPS or rubidium to calibrate the
internal one just before you need some more accurate absolute
frequency measurements on the SA.
It will depend on what measurement you are making, and whether phase
noise or frequency accuracy is more important. For day to day use,
the external ref will work, except when perhaps you need to look at
very close skirts, where maybe the internal alone can give you lower
noise. In most cases, you don't really need either (checking a
filter, EMI, radio output, etc.) but a lot of thing in this list is
because we can, not because we need. :-)
Get a real clean, low phase noise 3rd signal, measure it using the
internal and external osc, look at the skirts. They might even be the
same, if the limit is elsewhere in the SA signal chain.
One other thing is that some spectrum analyzers aren't really designed
for low noise performance. Since the noise floor is often pretty high,
the design of the whole RF chain (e.g. spur levels and such) might
have assumed that lots of things would be hidden in the grass. If the
analyzer is of the recent "bring a band of RF down to an IF, sample
and FFT it for fine resolution" architecture, such things as the
number of bits in the ADC and the "cleanliness" of the sampling clock
might have been chosen based upon doing 1024 point transforms being
displayed with 100dB dynamic range (10dB/div and 10 divisions).
(not to mention the spectrum analyzer actually generating spurious
signals. I ran across that one last year and thought I had an
interference source, but, no, went back and checked the spec sheet and
it said spurious are <-80dBc, and sure enough, there it was at -82
dBc. And stories about the first LO coming back out through the input
are legion.)
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