Spectrum Analyzer Menus
2715 User Manual
6–9
you to get an additional 10 dB of sensitivity by reducing the RF attenuation
10 dB and decreasing the IF gain 10 dB to compensate. The danger is that
internally generated distortion products may become more noticeable.
To change the signal level at the mixer, press [INPUT] [4].
You are prompted to enter a new mixer input level. You can enter values from
–50 dBm to –20 dBm in 2 dB steps. Try –20 dBm and –40 dBm while observing
the level of the noise. Because the RF attenuation is increased by the same
amount the first mixer input is decreased, and the noise floor rises as the mixer
level is reduced. When you are done experimenting, set the mixer input level
back to –30 dBm.
100.0MHz
(AUTO SWEEP)
ATTN 0DB
0.0DBMV
VF 300KHz
5MHz/
10 DB/
300KHz RBW (AUTO)
The 2715 is equipped with an internal preamplifier. The preamplifier can be very
useful when measuring cable TV noise (see Measuring Carrier-to-Noise Ratios
on page 6–46) or other signals near or below the normal 2715 noise floor. It is
also useful for increasing the sensitivity of radiated RF energy measurements
(leakage, etc.). The nominal gain in sensitivity using the preamplifier is 12 dB.
Above 600 MHz the preamplifier remains usable and useful, but its flatness rolls
off somewhat and is not specified. To be effective, the preamplifier must be used
with no RF attenuation. The preamplifier is not normally turned on, because it
can easily result in overdriving the first mixer. The signal amplitude at the first
mixer with the preamplifier on and no RF attenuation is equal to the input signal
level plus approximately 18 dB (that is, a 10 dBmV signal would probably
overdrive the first mixer). Total signal amplitude greater than 0 dBmV at the
input to the 2715 with the preamplifier turned on may create spurious signal
components and produce unreliable amplitude measurements.
Note the level of the noise floor and then press [INPUT] [1].
Item 1 of the INPUT menu toggles the preamplifier on and off. The preamplifier
is now turned on as indicated by the term PRE following the reference level
readout.
Again note the noise floor. It should be approximately 12 dB lower than before.
The 2715 has automatically reduced its internal gain (thus lowering the normal
noise floor) to compensate for the added gain of the preamplifier. The result is
that you can now see signals that are up to 12 dB below the normal 2715 noise
floor. Toggle the preamplifier off.
Turning the Preamplifier
ON/OFF
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