Introduction; Operating Instructions - Hameg Instruments Hm5012-2 Handbuch

Introduction

Introduction
The spectrum analyzer permits the detection of spectrum
components of electrical signals in the frequency range of
0.15 to 1050MHz. The detected signal and its content have to
be repetitive. In contrast to an oscilloscope operated in Yt
mode, where the amplitude is displayed on the time domain,
the spectrum analyzer displays amplitude on the frequency
domain (Yf). The individual spectrum components of „a signal"
become visible on a spectrum analyzer. The oscilloscope
would display the same signal as one resulting waveform.
The spectrum analyser works according to the double superhet
receiver principle. The signal to be measured (fin = 0.15MHz
to 1050MHz) is applied to the 1st mixer where it is mixed with
the signal of a variable voltage controlled oscillator (fLO
1350,7MHz – 2400,7MHz). This oscillator is called the 1st LO
(local oscillator). The difference between the oscillator and
the input frequency (fLO - fin = 1st IF) is the first intermediate
frequency, which passes through a waveband filter tuned to a
center frequency of 1350,7MHz. It then enters an amplifier, a
second mixing stage, oscillator and the second IF amplifier
(10.7MHz). In the latter, the signal can be selectively transferred
through a filter with 1000kHz, 120kHz or 9kHz bandwidth
before arriving at an AM demodulator. The logarithmic output
(video signal) is transferred directly, or via a low pass filter to
an A/D converter and the signal data are stored in a RAM. The
lowest frequency of a span is stored at the lowest address
and the highest frequency at the highest address. Then the
next span starts the same procedure once again. This means
that the signal data are continuously updated.
In addition the signal data are read and converted by a D/A
converter into an analogue signal. The latter controls the Y
amplifier and the Y deflection plates of the CRT.
With increasing signal level (amplitude) the beam is deflected
from the bottom (noise) to the top of the screen.
During the continuous read process the RAM becomes
addressed from the lowest to the highest address. The
addresses become D/A converted and consequently generate
a saw tooth signal which controls the X deflection. The sweep
starts with the lowest frequency (address) at the trace start
(left) and ends with the highest frequency (address) at the
trace end (right).
The stored spectrum data can be transferred to a PC via the
built in serial interface.
Note: In Zero Span mode the measuring frequency does not
change. Then the X deflection is a time function.
The HM5014-2 also includes a tracking generator. This
generator provides sine wave voltages within the frequency
range of 0.15 to 1050MHz. The tracking generator frequency
is determined by the first oscillator (1st LO) of the spectrum
analyzer section.
Spectrum analyzer and tracking generator are frequency
synchronized.
32

Operating Instructions

It is very important to read the instructions including the
paragraph „Safety" prior to operating the HM5012-2/HM5014-
2. The straightforward front panel layout and the limitation to
basic functions, guarantee efficient operation immediately.
To ensure optimum operation of the instrument, some basic
instructions need to be followed.
Prior to examining unidentified signals, the presence of
unacceptable high voltages has to be checked. It is also
recommended to start measurements with the highest
possible attenuation and a maximum frequency range (Span
1000MHz). The user should also consider the possibility of
excessively high signal amplitudes outside the covered
frequency range, although not displayed (e.g. 1200MHz). The
frequency range of 0Hz to 150kHz is not specified for the
HM5012-2/HM5014-2 spectrum analyser. Spectral lines within
this range would be displayed with incorrect amplitude.
High intensity settings should be avoided. The way signals
are displayed on the spectrum analyser typically allows for
any signal to be recognized easily, even with low intensity.
Due to the frequency conversion principle, a spectral line is
visible at 0Hz. It is called IF feedthrough. The line appears
when the 1 st LO frequency passes the IF amplifiers and filters.
The level of this spectral line is different in each instrument. A
deviation from the full screen does not indicate a
malfunctioning instrument.
Subject to change without notice