2. For a 1 dB loss of sensitivity, read the ΔDynamicRange from the red curve as 7 dB.
3. Read the required noise ratio R vertically on the dashed green curve as 6.1 dB.
4. Check that the RF/IF gain brings the front-end thermal noise at -112 dBm/MHz up to a
level that is 6.1 dB higher than the IFD noise density of -87 dBm/MHz.
The gain does not depend on bandwidth, and therefore is correct for all pulse width/
bandwidth combinations. The gain is:
(-87 dBm/MHz+6 dB) - (-112 dBm/MHz) = 31 dB
5. Calculate the dynamic range for the complete system at 0.5 MHz bandwidth as 106 dB -
6 dB = 100 dB.
6. After assembling all of the RF and IF components, check whether you have the correct
gain by verifying a 7 dB rise (independent of bandwidth) in RVP900
filtered power,
when the IF- Input cable is connected and disconnected.
4.2.12
Configuring IF Gain Based on System Noise Figure
Every amplifier can be partially characterized by its gain G and noise figure F.
When computing the front-end RF/IF gain based on the system noise figure, gain is
measured by injecting a test signal at the mid- power range of the
amplifier and measuring
the ratio of Output/Input power.
Noise figure is measured by terminating the input of the amplifier, measuring the output
power within some prescribed bandwidth, and then dividing by the thermal noise power
expected over that same bandwidth from an ideal
amplifier having the same gain. For
example, suppose that an amplifier with a gain of 20 dB delivers -90 dBm of output power
within a 1 MHz bandwidth when its input is terminated. We would expect the Boltzman
thermal input noise, at -114 dBm/MHz, to produce -94 dBm, from an ideal 20 dB
amplifier,
under the same conditions. The noise figure of the real amplifier is +4 dB, (-90 minus -94).
Although the above
definitions are typically applied to linear analog amplifiers, these same
terms can be applied to hybrid analog/digital systems such as RVP900.
• To calculate the gain of the RVP901 IFDR, we apply a calibrated mid-power signal
generator directly to its IF-Input, and use the Pr plot to print the measured power.
For a wide range of analog input power levels, RVP900 reports the same measured
digital power; therefore the overall analog/digital gain is 1.0 (0 dB).
See 6.7 Pr — Plot Receiver Waveforms (page 155).
• To calculate the noise
figure of the RVP901 IFDR, we set the receiver bandwidth to 1
MHz, terminate the IF-Input in 50 Ω, and use the Pr plot, this time to examine the in-
band thermal noise power.
The measured noise level is around -87 dBm. Since an ideal unity gain
amplifier has
produced a noise power of -114 dBm in an equivalent bandwidth, the noise
figure of the
RVP901 IFDR is 27 dB.
See 6.6.2 Ps Subcommands (page 140).
Chapter 4 – RVP Hardware
71
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