Installation Instructions

Hardware Installation
RVP8 User’s Manual
September 2005
2–13
3. Thus, the RF/IF gain must bring the front-end thermal noise at –112dBm/MHz up
to a level that is 6.1dB higher than the IFD noise density of –82dBm/MHz. The
gain is therefore (–82dBm/MHz + 6dB) – (–112dBm/MHz) = 36dB. Note that
this gain does not depend on bandwidth, and therefore will be correct for all
pulsewidth/bandwidth combinations.
4. The dynamic range for the complete system at 0.5MHz bandwidth may now be
calculated as 101dB – 7dB = 94dB.
5. After assembling all of the RF and IF components we can check whether we
achieved the correct gain by verifying a 7dB rise (independent of bandwidth) in
RVP8 filtered power when the IF-Input cable is connected versus disconnected.
Keep in mind when designing your RF and IF components that the final amplifier driving the
IFD must be capable of driving up to, perhaps, +12dBm, so that signals above saturation can still
be correctly measured.
2.2.9 IF Gain Based on System Noise Figure
The previous section described how to compute the front-end RF/IF gain based on the desired
tradeoff of dynamic range versus sensitivity. Since arriving at the proper gain is so important,
we present an alternate but equivalent approach based on system noise figure.
Every amplifier can be partially characterized by its gain “G” and noise figure “F”. Gain is
measured quite simply by injecting a test signal at the mid-power range of the amplifier and
measuring the ratio of Output/Input power. Noise figure is a little trickier, and 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 20dB delivers –90dBm of output power within a 1MHz bandwidth when its input is
terminated. We would expect the Boltzman thermal input noise at –114dBm/MHz to produce
–94dBm from an ideal 20dB amplifier under the same conditions. The noise figure of the real
amplifier is therefore +4dB, i.e., –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 the RVP8.
S To calculate the gain of the RVP8/IFD we apply a calibrated mid-power signal generator
directly to its IF-Input and use the Pr plot (Section 4.5) to print the measured power. For
a wide range of analog input power levels the RVP8 will report the exact same measured
digital power; hence the overall analog/digital gain is 1.0 (0 dB).
S To calculate the noise figure of the RVP8/IFD, we set the receiver bandwidth to 1MHz
(Section 4.4.2), terminate the IF-Input in 50-Ohms, and again use the Pr plot, this time to
examine the in-band thermal noise power. For the Rev.D IFD this measured noise level
will be around –82dBm. Since an ideal unity gain amplifier would have produced a
noise power of –114dBm in an equivalent bandwidth, the noise figure of the RVP8/IFD
is 32dB.