Sensitivity - Maximum Input Levels; Frequency Response; Tracking Generator; Concept Of The Hm 5510 - Hameg HM5510 Mode D'emploi

Sensitivity – Maximum input levels
The specification of spectrum analyzer sensitivity is not uni-
form. One method defines the sensitivity as the input level at
which the signal power is identical to the average noise power
of the analyzer. As an analyzer measures signal plus noise
the signal will appear 3 dB higher than the noise in case the
above definition holds.
The maximum input level of an analyzer is the level which is
safe for the input stage which does not mean that at such level
the instrument will still measure within spec. Customarily,
the level is considered maximum usable at which a
compression of 1 dB takes place. The permissible level is
dependent upon the input attenuator setting. When using an
analyzer it is good practice to always start with maximum
attenuation switched in and then decreasing it. See the
specifications for the numbers.
The input stage may be overdriven without that this will be
clearly displayed in any case. Hf energy outside the
instrument's useful band of 150 kHz to 1050 MHz may e.g.
cause input overdrive.
Due to nonlinearities in the input stage it is always advisable
to use the highest attenuation setting of the input attenuator
which is commensurate with a good display. The distortion
products generated by the HM 5510/11 remain < –75 dB if the
input level after the attenuator remains < –30 dBm.

Frequency response

As with any system the frequency response should be flat over
the useful band in order to assure that the accuracy of the
amplitudes displayed is independent of frequency. Filters and
amplifiers must have reached steady state levels.
Tracking generator (HM 5511 only)
A tracking generator is a built-in sine wave generator the
frequency of which is identical to the frequency setting of the
analyzer i.e. its frequency is always in the center of the band-
pass.
Signal harmonics from the tracking generator or generated
elsewhere in the analyzer thus fall outside the displayed
window . The sensitivity of the system is determined by the
noise level and the bandwidth. The smallest usable bandwidth
will depend on the tracking generator's residual FM.
The spectrum analyzer with tracking generator allows
measurements of frequency response and gain resp.
attenuation of amplifiers, filters etc. The tracking generator
output is fed into the unit under test and its output into the
spectrum analyzer input. The output level of the generator is
kept constant by an amplitude control loop. Also standing wave
measurements are thus possible.
I n t r o d u c t i o n t o t h e o p e r a t i o n o f H M 5 5 1 0 / 1 1
HM 5510/11 are spectrum analyzers for the range of 150 kHz
to 1050 MHz. The signal to be analyzed must repeat
periodically.
The analyzer uses the superheterodyne principle. The 1
mixes the input with the local oscillator signal and converts
the signal to the 1
different IFs. The 3
kHz.
Display (CRT)
Following the detector the signal passes a logarithmic
amplifier and is directly or via a video filter fed to the vertical
deflection amplifier. The X axis amplifier receives a sawtooth
sweep signal. The lowest frequency corresponds to the 1st
(left) graticule line, the highest to the last (10
STOP
With zero span there is no sweep, the frequency
remains constant.
TiPP
operation of HM5511 / HM5510
Turn-on.
Please observe the following hints prior to first-
time operation.
– Check whether the correct type of fuse is inserted.
– Mains outlet conforms to safety standards, i.e. it has a
safety earth pin.
– No visible damage
– Line cord undamaged
– No loose parts in the instrument.
Operation
The instrument is easy to operate, nevertheless please observe
the following precautions:
The most sensitive part of the instrument is the
input stage. It consists of an attenuator, a filter and
the 1
STOP STOP
following input levels must not be exceeded:
±10 dBm = 0.7 Vrms (hf)
± -25 V
With the attenuator at – 40 dB:
– 20 dBm (hf).
Higher levels may destroy the input stage.
Concept of HM5510 / 11
st
IF. There are 2 more mixer stages with
rd
IF filter can be switched from 500 to 20
Introduction to the
st
mixer. With the attenuator at 0 dB the
DC
Subject to change without notice
st
mixer
th
).
33