Transmit Signalling Circuits
Introduction/Theory of Operation
3.1-13
5.2
High Speed Data
High speed data refers to the 3600 baud data waveforms, known as Inbound Signalling Words
(ISWs) used in a trunking system for high speed communication between the central controller and
the radio. To generate an ISW, the
µ
P first programs the ASFIC (U0201) to the proper filter and gain
settings. It then begins strobing U0201-G1 (TRK CLK IN) with a pulse when the data is supposed to
change states. U0201’s 5-3-2 State Encoder (which is in a 2-state mode) is then fed to the post-
limiter summer block and then the splatter filter.
From that point it is routed through the modulation attenuators and then out of the ASFIC to the RF
board. MPT 1327 and MDC are generated in much the same way as Trunking ISW. However, in
some cases these signals may also pass through a data pre-emphasis block in the ASFIC. Also
these signalling schemes are based on sending a combination of 1200 Hz and 1800 Hz tones only.
Microphone audio is muted during High Speed Data signalling.
5.3
Dual Tone Multiple Frequency (DTMF) Data
DTMF data is a dual tone waveform used during phone interconnect operation. It is the same type of
tones which are heard when using a ”Touch Tone” telephone.
There are seven frequencies, with four in the low group (697, 770, 852, 941Hz) and three in the high
group (1209, 1336, 1477Hz).
The high-group tone is generated by the
µ
P (U0101-5) strobing U0201-G1 at six times the tone
frequency for tones less than 1440Hz or twice the frequency for tones greater than 1440Hz. The low
group tone is generated by the
µ
P (U0101-7) strobing U0201-G2 (DTMF CLCK) at six times the tone
frequency. Inside U0201 the low-group and high-group tones are summed (with the amplitude of the
high group tone being approximately 2 dB greater than that of the low group tone) and then pre-
emphasized before being routed to the summer and splatter filter. The DTMF waveform then follows
the same path as was described for high-speed data.
Summary of Contents for GM1200E
Page 2: ...ii ...
Page 4: ...Cautions and Warnings iv ...
Page 6: ...Cautions and Warnings vi ...
Page 8: ...Contents viii Detailed Service Manual ...
Page 10: ...Table of Contents 1 ii Introduction ...
Page 14: ...Table of Contents 2 ii Control Head Level 3 Information ...
Page 16: ...Table of Contents 2 1 ii Introduction Theory of Operation ...
Page 24: ...Table of Contents 2 2 ii PCB Schematic Diagram and Parts List ...
Page 26: ...Table of Contents 3 ii UHF VHF Radio Level 3 Information ...
Page 30: ...Table of Contents 3 1 iv Introduction Theory of Operation ...
