Mototalk [Available Only On I290] - Motorola i425e Detailed Service Manual

Reference Oscillator
The 33.6 MHz referen
reference frequency for the internal synthesizers. This 33.
routed ROADRUNNER IC and is frequency divided down to a 4.2 MHz to serve as a reference
for JANUS (TCLK).
1.9

MOTOtalk [Available ONLY on i290]

The p p ur ose of the MOTOtalk feature is to allow simple, dire
comm unications between subscriber units. It is also asynchronous in nature and requires no
exter nal source of synchronization for connections between units to be made. The basic features
of M OTOtalk are as follows:
•
Digital 2-Way radio, P
• 2200 bps AMBE++ Vocoder (same as iDEN enhanced 12:1 vocod
• Frequency Hopping Spread Spectrum in the 902-928 MHz Industrial, Scientific, and
medical (ISM) Band.
•
Three-bu rst frequency diversity for all burst types.
• 10 User-selected Channels (actually hop-sets of 50 carriers each).
• 15 User-Selected Codes (plus "Receive All" acting as an open-squelch, open-receive
mode).
• Private mode operation using target's 10-digit phone number as the ID.
•
1 Watt RF Powe
any particular hop-set.
• 8-level Frequency Shift Ke
(hop intervals).
• Each on a pseudo-randomly selected frequency.
• Symbol Rate: 3200 baud.
•
Mototalk operates in the 900 MHz ISM band, frequency range (902 – 928 MHz). The
m odulation varies between 2FSK, 4FSK, 6FSK, or 8FSK. Traffic use
K eying (8FSK) modulation with a 50 kHz bandwidth and symbol rate of 3200 symbols per second.
8 FSK modulation results in a signal with 3 bits per symbol (raw). Error! Reference source not
und.3 shows the MOTOtalk power spectrum for 8FSK modulation.
fo
6880401P26-O
ce is sourced to Sledgehammer to serve as a stable and accurate 33.6 MHz
ush-to-Talk (PTT) operation
r, 50 kHz carrier spacing, 500 kH
ying (8FSK) modulation, 85.625-ms bursts at 90-ms intervals
Figure 12: MOTOtalk 8FSk Spectrum
OVERVIEW: iDEN Digital Modulation Technolo
6 MHz reference signal is additionally
ct, simplex two-way radio-to-radio
.
er).
z separation between adjacent carriers in
s 8-level Frequency S
gy
hift
33