Hameg HM8135 User Manual page 33

The modulation is turned on by pressing the context sensi-
tive key below the string OFF. One time for turning the
5
internal source on (INT) and a second time for turning the
external source on (EXT). The active source is pointed out
by a triangle beside the option.The indicator LED of the
MOD.OUTPUT is lighting.
Pressing the context sensitive key
dulation will be deactivated (OFF).
The return to the previous menu is possible by pressing
the PREV. key .
3
With external AM activated, the only modifiable op-
tion is the modulation depth (see paragraph "Amplitude
modulation").
The external modulation frequency for AM must be in the
range: 10 Hz to 100 kHz
With external FM or PM activated, several cases are
possible:
❙ DC coupled (DC – 100 kHz)
❙ AC coupled (100 Hz – 100 kHz)
❙ Deviation (see corresponding paragraph)
Example 1:
CH1: modulation: first pulse width 150 s
second pulse width 1.1 ms
period 2.5 ms (Fmod: 400 Hz)
CH2 moduled signal (deviation: 2 kHz)
once again, the mo-
5
Example 2:
In this example, the external modulation signal is a "tri-
nary" code composed of 9 bits. One bit is composed of 2
narrow and / or wide pulses, depending on the combina-
tion expected:
❙ A bit composed of 1 wide and 1 narrow pulses is called
OPEN.
❙ A bit composed of 2 narrow pulses is called LOW.
❙ A bit composed of 2 wide pulses is called HIGH.
For detecting the first bit, a synchronisation bit (long low
level) is present. The modulation frequency is 20 Hz.
CH1: modulation: narrow pulse of 200 µs
wide pulse of 1.8 ms
synchronisation bit of 14 ms
CH2: zoom of CH1
CH1: demodulated signal: DC coupled
CH2: demodulated signal: AC coupled
The return to the modulation menu is possible by pres-
sing the PREV. key and the return to the main display by
3
pressing the ESC key .
13
The external modulation input is on the front panel (MOD.
INPUT). The signal can be of any shape, however the AM-
depth and FM/PM deviation programmed is calibrated only
for a 2 V signal at the input.
RMS
Indroduction of the HM8135
33