User Manual

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Th e digital back-en d IC con sists of an am plifier, th e secon d m ixer, an
IF an alog-to-digital con verter, a baseban d down -con verter, an d a
2.4MHz syn th esis circuit to provide a clock to th e DSP-support IC on
th e vocoder board. Th e secon d LO is gen erated by discrete
com pon en ts extern al to th e IC. Th e output of th e digital back-en d IC
is a digital bit stream th at is curren t driven on a differen tial pair for a
reduction in n oise gen eration .
Th e tran sm itter con sists of an RF PA IC th at gets an in jection sign al
from th e VCO. Tran sm it power is con trolled by two custom ICs th at
m on itor th e output of a direction al coupler an d adjust PA con trol
voltages correspon din gly. Th e sign al passes th rough a RX/TX switch
th at uses PIN diodes to autom atically provide an appropriate in terface
to tran sm it or receive sign als. An ten n a selection is don e m ech an ically
in th e con trol top.
Cont roller Board
Basic Theory of
Operat ion
Th e con troller board con tain s th e radio’s m icrocon trol un it with its
m em ory an d support circuits, voltage regulators, audio, an d power
con trol circuits. Con n ected to th e con troller board are th e display
board, RF board, vocoder board, keypad board, con trols/un iversal flex,
an d (option al) en cryption m odule.
Th e m icrocon trol unit con trols receive/tran sm it frequen cies, power
levels, display, an d oth er radio fun ction s, usin g eith er direct logic
con trol or serial com m un ication s path s to th e devices.Th e
m icrocon trol un it executes a stored program located in th e FLASH
ROM. Data is tran sferred to an d from m em ory by th e m icrocon trol
un it data bus. Th e m em ory location from wh ich data is read, or to
wh ich data is written , is selected by th e address lin es.
Th e support-logic IC acts as an exten sion of th e m icrocon trol unit by
providin g logic fun ction s such as lower address latch , reset, m em ory
address decodin g, an d addition al con trol lin es for th e radio. Th e
m icrocon trol un it con trols th e crystal-pull circuit to adjust th e crystal
oscillator’s frequen cy on th e m icrocon trol un it, so th at th e E-clock’ s
h arm on ics do n ot cause in terferen ce with th e radio’s receive ch an n el.
Th e regulator an d power-con trol circuits in clude an un switch ed +5V
discrete circuit an d th e regulator/power-con trol IC. Switch ed +5V is
used for all circuits on th e con troller board except th e audio PA, wh ich
is sourced from 7.5V. Th e regulator autom atically provides 5V wh en
th e radio is turn ed on . Th e regulator’s power-down m ode is con trolled
by th e m icrocon trol un it, wh ich sen ses th e position of th e on /off
switch .
Vocoder Board
Basic Theory of
Operat ion
Th e vocoder board con tain s th e digital-sign al processor (DSP), its
m em ory devices, an d th e DSP-support IC.
Th e DSP perform s sign allin g an d voice en codin g an d decodin g as well
as audio filterin g an d volum e con trol. Th is IC perform s Private-Lin e®/
Digital Private Lin e™ (PL/DPL) en code an d alert-ton e gen eration . Th e
IC tran sm its pre-em ph asis on an alog sign als an d applies a low-pass
(splatter) filter to all tran sm itted sign als. It requires a 33MHz crystal to
fun ction . An 8kHz in terrupt sign al gen erated by th e DSP-support IC is