CONVENTIONAL AM SHORT WAVE TRANSMITTERS

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CONVENTIONAL AM SHORT WAVE TRANSMITTERS Class
B Modulation The HT voltage variation achieved
by Modulation Transformer.
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DISADVANTAGE OF CONVENTIONAL AM SHORT WAVE
TRANSMITTERS Efficiency is less i. e about
60 at 100 modulation. Recurring cost of
transmitting tubes due to ageing . No
redundancy ( Fault in one tube causing
deterioration in audio quality ).
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THE ADVANTAGES OF PSM TRANSMITTERS The principal
advantages of the PSM system are - high
overall efficiency of the complete transmitter
no costs for replacement of modulator tubes
possibility of high-power SSB operation
possibility of dynamic carrier control
elimination of need for crow-bar protection.
Reliability and redundancy
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PULSE SYSTEM MODULATION The pulse system
modulator feeds the transmitter RF final stage
with an amplitude-modulated power supply
voltage. The pulse modulator thus supplies the
carrier power as well as the modulation
power. The digital processing of the
audio-frequency signal results in a very stable
and practically maintenance free
operation. Oscillation as they may be
encountered in traditional Class B modulation
will not appear, because digital limiters
prevent any overshooting of the output voltage.
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COARSE SYSTEM MODULATION The output voltage
may be varied step-wise from zero to the double
value of the DC carrier voltage by changing the
number of modules switched off.
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FINE MODULATION The coarse modulation cannot
provide an exact adaptation of the output
voltage to the desired value. The error
thus resulting will have to be corrected by
means of superimposing the coarse-step
modulation with a pulse duration modulation.
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DRM INTERFACE DRM Modulation / RF Exciter
STRATUS. Multiplexer CIRRUS.
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PSM FILTER Wider bandwidth for signal
processing is needed. The PSM filter must be
adjusted to suit the new requirements. Amplitu
de and phase response in digital operation must
be linear up to at least 35 kHz.
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PSM FILTER Wider bandwidth for signal
processing is needed. The PSM filter must be
adjusted to suit the new requirements. Amplitu
de and phase response in digital operation must
be linear up to at least 35 kHz.
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PSM FILTER Wider bandwidth for signal
processing is needed. The PSM filter must be
adjusted to suit the new requirements. Amplitu
de and phase response in digital operation must
be linear up to at least 35 kHz.
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LIMITATIONS OF DRM STANDARD FOR SW
TRANSMITTERS RF-Bandwidth is limited to 10
kHz. Simulcast operation is possible for
test purposes, but no statements can be made
about the quality of the signal in simulcast
operation since the filter is optimized for
digital operation. DRM operation of the
transmitter is only possible when the DRM
Modulator / RF Exciter STRATUS is driver by a
DRM / DI-MDI signal which is conform to the DRM
Standard. The DRM Multiplexer CIRRUS delivers
this signal.
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DRM TRANSMISSION ITS UTILITY DRM started in
India on Jan 26, 2007. Supports text-data
transmission. Programme available on the
special DRM receiver not on the normal SW
receiver. When a listener is listening to a
song we can let the listener see the name of the
movie, the name of the singer, composer, on the
LCD screen on the Radio. Real time messages
viz. Stock Market, Railway information, breaking
news etc. can be displayed on the LDC screen of
the DRM Receiver.
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ADVANTAGES OF DRM TRANSMISSION The two big
advantages of DRM is that it can be broadcast
via existing AM transmitters, so no need for all
that expensive investment. Second, and more
important, DRM signals are stronger and can be
broadcast for much longer distances than DAB.
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RECEIVERS FOR DRM
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THANK YOU