WARNING: I started this off as a general answer to your question because I didn't know the answer. So this is not for you, but for me, future me, and future people to form a better formatted answer to the general question: what is the equation for spectrum analyzer dynamic range? I got bored and stopped before I finished.
So a ideal spectrum analyzer has a both a maximum power level and an absolute-minimum power level (or noise floor, or displayed average noise level (
DANL)). An ideal spectrum analyzer would have an ideal display, an ideal mixer, and presumably ideal preamplifier, attenuators, and amplifiers.
It looks like the equation the overall dynamic range of a spectrum analyzer is:
rangemeasurement + rangedisplay + noiseDANL + noisespurious + noisephase = Dynamic Range
You've heard of some of these before:
- rangedisplay is borne from the fact that the any display device has a maximum and minimum intensity.
- rangemeasurement is the difference between the largest signal from the most attenuated input setting to the smallest signal from the least attenuated setting.
- noisespurious is the amplitude of the spurious tones created by the instrument's amplifiers and mixers.
- noiseDANL is the Displayed Average Noise Level, or noise floor or sensitivity.*
- noisephase is the instability caused by mixing the signal with the inherently unstable local oscillator (LO)
- HINT: Ignoring rangedisplay, notice the impact from each component of the dynamic range decreases from left to right:
- rangemeasurement (-151dBm and up from Figure 1)
- noiseDANL (-135 dBm and up)
- noisespurious (97 and 90 dB of range above the -135dBm floor)
- noisephase (the 80 dB of range left over when you set your reference to minimize phase noise)
- HINT: noiseDANL is the "key" property when measuring two signals that are far apart in frequency (in contrast to phase noise)
- HINT: noisephase behaves like third order inter-modulation (TOI) distortion: it is most significant when the input signal has two tones that are nearby to each other (less than 1 MHz) -- at least for purposes of dynamic range
Even if we don't fully understand all of these, we use some relationships, hints, and assumptions to simplify our question:
First, we work under the assumption that a wide signal is similar enough to two thin signals spaced apart by the width. This is a simplification used in tons of testing procedures, and it's the analysis of
inter-modulation distortion. The two unhighlithed tones f
1 and f
2 are the inputs. I
think, however, that in your specific case we don't need to consider this both because it doesn't mention two tones
and because the RBW is only 300 Hz, which is much smaller than 1 MHz.
According to
this paper (from which this response is almost entirely plagiarized),
after we set our reference (mixer level) just right (right where our second-order and third-order distortion curves meet), then the dynamic range is equal to the
equality of these two equations:
range3rd = (2/3) * ( DANLactual - TOI )range2nd = (1/2) * ( DANLactual - SHI )TOIa = mixer level - (1/2) (distortion products in dBc)
SHIb = mixer level - (distortion products in dBc)
DANLactual = DANL
at 1 Hz - 10 log ( DANL
at your RBW / DANL
at 1 Hz )
So, having typed all of this out, I think you have enough to know where to look in the
manual you linked to find the DANL at 1 Hz, then find the right mixer level at 1.2 GHz; converting your answer to the 300 Hz RBW (which happens to be the minimum RBW for that instrument).
- a Third Order Intercept (point). Also called IP3.
- b Second Harmonic Intercept (point). Also called SOI or IP2.
- * DANL actually has a physical absolute minimum of -174 dBm derived from its defining equation:
DANLmin = kTB.
- k is Boltzmann's Constant (which has dimensions of [energy] / [temperature], I'm sure I do need to remind you. I needed to remind me.).
- T is temperature which has dimensions of ... [temperature], and units of [Kelvin].
- B is bandwidth which has units of [frequency], we're going to use [Hertz].
Apparently, if you are bored enough to multiply these together, (or even to just do the dimensional analysis, honestly) you will find that these are in units of power and calculated at room temperature and 1 Hz (a standard for some reason), you really do get -174 dBm.
[/list]