Test Signal Display; Functional Principle - Hameg Instruments HM5014-2 Manual Del Usuario

T e s t S i g n a l D i s p l a y
Reference Level
Graticule Line
Memory A(Sample),
B or A-B
48 MHz Test Signal ON
Marker Level (RO)
Marker Frequency (RO)
Center Frequency (RO)

Functional principle

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 (fi n = 0.15 MHz to 1050
MHz) is applied to the 1st mixer where it is mixed with the signal of a
variable voltage controlled oscillator (fLO 1350,7 MHz – 2400,7 MHz).
This oscillator is called the 1st LO (local oscillator). The difference
between the oscillator and the input frequency (fLO - fi n = 1st IF) is
the fi rst intermediate frequency, which passes through a waveband
fi lter tuned to a center frequency of 1350,7 MHz. It then enters an
amplifi er, a second mixing stage, oscillator and the second IF ampli-
fi er (10.7 MHz). In the latter, the signal can be selectively transferred
through a fi lter with 1000 kHz, 120 kHz or 9 kHz bandwidth before
arriving at an AM demodulator. The logarithmic output (video signal)
is transferred directly, or via a low pass fi lter to an A/D converter and
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Subject to change without notice

Test Signal Display

Center Frequency Graticule Line
Reference Level (RO)
Span (RO)
Tracking Generator Output Level (RO)
Tracking Generator ON
(RO) = Readout
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 amplifi er and the Y de-
fl ection plates of the CRT. With increasing signal level (amplitude) the
beam is defl ected 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 conver-
ted and consequently generate a saw tooth signal which controls the
X defl ection. 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: While Zero-Span-Mode the measuring frequency
does not change and the X-defl ection is a time depending
function.
The HM5014-2 also includes a tracking generator. It provides sine wave
STOP
voltages within the frequency range of 0.15 to 1050 MHz. The tracking
generator frequency is determined by the fi rst oscillator (1st LO) of
the spectrum analyzer section.