Motorola RADIUS GM300 서비스 매뉴얼 - 페이지 31

{카테고리_이름} Motorola RADIUS GM300에 대한 서비스 매뉴얼을 온라인으로 검색하거나 PDF를 다운로드하세요. Motorola RADIUS GM300 49 페이지. 16-channel, conventional fm radio
Motorola RADIUS GM300에 대해서도 마찬가지입니다: 서비스 매뉴얼 (28 페이지), 사용 설명서 (18 페이지), 사용 설명서 (19 페이지), 사용자 설명서 (37 페이지), 운영 지침 (2 페이지)

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Theory of Operation

Logic Board

the logic board. Q277 conducts to supply TX 8.5V, and

Q278 saturates across the base-emitter of Q279, turning

it off.

Each VCO consists of a FET oscillator whose frequency

is determined by a parallel L-C network consisting of a

tunable coil and a network of varactors. As the steering

line varies over the range of 2V to 7.8V DC, the capaci-

tance of the varactors decreases as voltage is raised,

causing the oscillator frequency to increase. The trans-

mit VCO has an additional varactor, CR208, which is

very lightly coupled to the tank circuit, which provides

frequency modulation of the VCO from the audio sig-

nal applied at J6-10 and adjusted by VCO MOD adjust

pot R302.

Each VCO has an AGC rectiÞer circuit (CR206 or

CR214) which varies the DC gate bias on the VCO FET

as a function of the RF output level at the VCOÕs drain.

This helps maintain a more constant VCO output level,

and prevents RF voltages from increasing to levels

which might cause rectiÞcation by the varactors.

Transistors Q204, Q205 are receive buffer ampliÞers.

These raise the RF output of the VCO to the level

required as injection for the Þrst mixer, typically

between +5 and +13 dBm depending on the frequency

band, as detailed in sections 1.1 and 1.2. The RF at

Q205Õs base is sampled and fed back to the synthesizer

via buffer Q107, allowing the synthesizer to ÒknowÓ if

the VCO is operating at the correct frequency.

Similarly, transistors Q207, Q208 are transmit buffer

ampliÞers. These raise the RF output of the VCO to the

level required by the RF power ampliÞer, typically +13

to +14.5 dBm, as measured at J5, which is a 50 ohm

port. The VCO frequency is sampled at Q208Õs base

and fed back to the synthesizer via buffer Q107.

Logic Board

There are two versions of logic boards used in GM300

series mobile radios, ÒmaskedÓ and Òexpanded.Ó The

expanded logic board has a shielded compartment

which encloses the microcomputer, custom gate array,

and external memory ICÕs, and has a four-layer printed

circuit board layout. The masked logic board uses a

two- layer circuit board without the shielded compart-

ment, with all software functions contained in a single

masked microcomputer IC. In general, the masked

logic board is used in 2 and 8 channel models with

basic signaling capabilities, while the expanded logic

board is found in 16 channel models having more elab-

orate signaling systems or requiring programmable

accessory connector I/OÕs.

The logic board circuitry consists of Þve major sections:

¥ DC distribution and regulation

¥ Microcomputer and logic

2-6

¥ Receiver audio circuitry

¥ Transmitter audio circuitry

¥ Transmitter power control circuitry

DC Distribution and Regulation

All operating voltage for the radio is supplied from the

RF power ampliÞerÕs battery input connector J2. This

voltage is protected from reverse polarity or excessive

positive transients by CR2270, CR2370, CR2470,

CR2570, CR2670 or CR2770 (depending on power

ampliÞer kit), which acts as a power diode for reverse

polarity protection, as well as a power transient sup-

pressor due to its reverse avalanche characteristics. The

supply voltage is routed to the logic board via J7-5

(UNSW B+).

Whenever UNSW B+ is supplied, a continuous source

of 5V DC is applied to pin 2 of the microcomputer from

the RAM 5V supply (VR402, CR403, R410 and C408).

This maintains the radioÕs scan list, current operating

mode, etc., when the radio is turned off. Due to the

storage of C408, this information can be maintained for

up to several hours even if the battery supply voltage

is interrupted.

When ignition control is not used, UNSW B+ via fuse

F801 becomes B+ which is routed through the on-off

switch to become SW B+. When ignition control is

used, fuse F801 is removed, and the vehicleÕs ignition-

switched voltage is supplied to J3-10 which is the B+

that is routed through the on-off switch to become SW

B+. Thus, with ignition control, ignition-controlled

voltage must be present at J3-10 for the radio to oper-

ate.

In 2-layer masked logic boards, when the radio is

turned on, SW B+ turns on Q404 via R414, which then

turns on Q403 via R412. When Q403 is on, UNSW B+ is

applied to to the supply pins of opamps U401 and

U451 (energizing the 9.6 volt regulator and transmitter

power control circuits). The low saturation voltage of

Q403 keeps the supply voltage of the transmitter

power control circuit essentially equal to the UNSW B+

voltage present in the RF Power AmpliÞer. This is

important for accurate power control operation. SW B+

is also routed to 5 volt regulator U402 (powering the

microcomputer and logic circuitry) and to J3-13, the

SW A+ sense pin on the accessory connector. The cur-

rent drawn through the on-off switch is relatively low,

less than 400 mA, and the majority is that required by

the 5V regulator. All high current stages, such as the RF

and audio power ampliÞers, operate from UNSW B+

and are controlled by low currents.

In 4-layer expanded logic boards, power distribution is

similar except that Q403 also switches the supply volt-

age to the 5 volt regulator IC U402. The higher current

drain from the 5V regulator due to the expanded logic

circuitry does not need to ßow through the radioÕs on-

68 No.

Name of Manual

March, 1997