65 Aleksandar Stamboliyski Str., 8000 Bourgas, Bulgaria
Tel: +359 56 820027, Fax: +359 56 836700
E-mail: [email protected] ,Web: www.devabroadcast.com
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Operation
RE-BROADCASTING LIMITATIONS
Signal Strength
The signal strength is a major factor when a signal is re-broadcasted, measured and evaluated.
FM compared to AM is less susceptible to the inherent noise of the radio reception.
When speaking about FM broadcasting, it is the monaural reception which can tolerate and
profit from a much narrower IF bandwidth. The stereo reception adds all noise present in the 23 –
53 kHz sub-band. The amplitude component (AM) of the sub band is converted down to audible
noise and added to the program signal. That is why the noise performance of FM-stereo can be as
much as 20 dB worse than that of monaural broadcast.
Better reception and measurement can be obtained by using highly directional outdoors antenna.
This will improve the signal strength and contribute in eliminating the multipath distortion.
Multipath Distortion
In FM reception, regardless of overall signal strength, a very important consideration is that
obstacles, which an FM signal may encounter in the line-of-sight path tend to reflect and disperse
the signal in many directions. In many locations, especially in urban areas where many tall
buildings interfere with the direct transmitted signal or in suburban areas surrounded by hills or
mountains, an FM receiver may pick up a station’s primary signal but, also, several secondary
reflections coming from various directions. These reflections arrive at the receiver out-of-phase,
slightly delayed in time with the primary signal and tend to blur or distort the principal signal. The
degree of distortion depends on the number and relative strength of the reflections.
The result, known as multipath distortion in FM reception can range from a low-level fuzziness
to a severely distorted sound quality, particularly at the high frequencies or treble. Multipath
distortion is especially troublesome in FM stereo reception.
DB7001 has a multipath distortion detector and Front panel multipath LED indicator with
adjustable threshold. A bar graph indicator representing the multipath level of the received signal
can be reached under
LEVELS
menu.
