5.0 Your first measurements / Modes
16
Often, you will not be able to exactly “hit” the center frequency of a signal, and
demodulation is bad or impossible. Thus, you can fine-tune the center fre-
quency using the
right/left arrow keys
. The step width used is derived
from the selected filter. Should you have chosen, for example, the 1MHz filter,
steps are 1MHz wide etc. When changing the center frequency, it will be shown
on the main INFO display (full MHz).
Examples:
- Cell towers/cell phones:
A
GSM900 / GSM1800 cell tower
(keys
7
/
8
) emits a “beeping” or “crackling”
noise with many interruptions and morse-like “pulsing”. This is the so-called
“control channel”, which is always active and “beeps” exactly at 1733,33Hz.
When one or more cellphones are active, you can recognize an additional
217Hz “crackling” noise (similar to morse code).
An optimal reproduction can be achieved with the 1MHz or 3MHz filter.
- DECT phones:
An easily recognizable signal source is the
base station of a DECT phone
(Key
0
). It produces a 100Hz “humming” sound. You can simply “prove” this by dis-
connecting the mains from the base station: the hum disappears. When you turn
the power back on, the hum will reappear after a few seconds.
Optimal reproduction is achieved by using the 1MHz filter.
ATTENTION:
for optimal reproduction of a signal, its level should be at least
-70dBm, even better stronger than -60dBm.
HINT:
Optionally, you can even
visualize
the demodulation using a LF spectrum
analyser. The SPECTRAN NF series lends itself optimally for this purpose, as
the NF-5010 and above offer the required signal input.
Summary of Contents for SPECTRAN HF-2025
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