Vertex Standard VXA-150 Manuel de service télécharger pdf (Page 11)

Circuit Description

Receive Signal Path

Incoming RF from the antenna jack is passed through

a low-pass filter and high-pass filter consisting of coils

L1022, L1024, L1026, L1027, L1030, & L1031, capacitors

C1237, C1239, C1242, C1245, C1247, C1248, C1249, C1250,

C1251, C1252, C1255, & C1257 and antenna switching di-

odes D1037 and D1039 (both RLS135) to the receiver front

end section.

Signals within the frequency range of the transceiver

are applied to the receiver front end which contains RF

amplifier Q1058 (2SC5226) and varactor-tuned band-pass

filter consisting of coils L1013, L1017, L1020, L1021, L1028,

& L1029, capacitors C1198, C1204, C1205, C1212, C1216,

C1217, C1222, C1228, C1232, C1243, & C1253, and diodes

D1032, D1034, D1036 & D1042 (all HVC350), then applied

to the 1st mixer Q1056 (2SC5226).

Buffered output from the VCO is amplified by Q1029

(2SC5226) to provide a pure 1st local signal between 143.4

and 172.4 MHz for injection to the 1st mixer. The 35.4 MHz

1st mixer product then passes through monolithic crystal

filter XF1001 (35S15A, 7.5 kHz BW) which strips away all

but the desired signal, which is then amplified by mixer

postamp Q1050 (2SC4215Y).

The amplified 1st IF signal is applied to the AM/FM IF

subsystem IC Q1049 (TK10931V), which contains the 2nd

mixer, limiter amplifier, and AM/FM detector.

A 2nd local signal is generated by PLL reference/2nd

local oscillator Q1045 (2SC4116GR) from the 17.475 MHz

crystal X1002. The 17.47 MHz signal is doubled by Q1048

(2SC4116GR) to produce the 450 kHz 2nd IF when mixed

with the 1st IF signal within Q1049. The 2nd IF then pass-

es through the ceramic filter CF1001 (ALFYM450F=K) to

strip away unwanted mixer products.

In the FM mode, a 2nd IF signal from the ceramic filter

CF1001 applied to the limiter amplifier section of Q1049,

which removes amplitude variations in the 450 kHz IF

before detection of the speech by the ceramic discrimina-

tor CD1001 (CDBM450C24T). Detected audio from Q1049

is passed through the de-emphasis, consisting of the re-

sistors R1089, R1095, R1100, & R1149, capacitors C1104,

C1105, C1107, & C1151, and Q1028-2 (NJM2904V).

In the AM mode, detected audio from Q1049 is passed

through the audio amplifier Q1028-1 (NJM2904V) and

ANL circuit, then applied to the AF amplifier Q1028-2

(NJM2904V). When ANL is on, the ANL MUTE gate

Q1027 (UMG2) goes high, the low-pass filer/limiter con-

sisting of capacitor C1124, resistors R1105, R1111, R1112,

R1115, & R1119 and diode D1023 (BAS316) is activate,

thus reducing the pulse noises when impulse noise re-

ceived.

The processed audio signal from Q1028-2 passes

through the audio mute gate Q1008 (DTC143ZUA) and

the volume control to the audio power amplifier Q1009

(TDA7233D), providing up to 0.4 Watts to the headphone

jack or 8 W loudspeaker.

A portion of the AF signal from the AM/FM IF sub-

system Q1049 converted into DC voltage within the IC,

and then passes through the AGC amplifier Q1054

(2SA1602A) and Q1055 (UMW1) to the inversion ampli-

fiers Q1051 and Q1057 (both 2SC5226). These amplifiers

reduce the gain of the IF amplifier Q1050 and the RF am-

plifier Q1058 while receiving a strong signal.

Squelch Control

When a signal is received, a DC squelch control volt-

age appears at pin 15 of AM/FM IF subsystem Q1049 ac-

cording to the receiving signal strength. This DC is ap-

plied to pin 2 of microprocessor Q1014.

The DC squelch control voltage is compared with the

SQL threshold level by the microprocessor Q1014. If the

DC squelch control voltage is higher, pin 49 of Q1014 goes

low. This signal disable the AF MUTE gate Q1008

(DTC143ZUA), thus activating the AF audio.

Also, the microprocessor stops scanning, if active, and

allows audio to pass through the AF MUTE gate Q1008.

Transmit Signal Path

Speech input from the microphone is passed through

the microphone sensitivity potentiometer VR1001 and

microphone amplifier Q1005-3 (NJM2902V), then applied

to the ALC amplifier Q1007 (AN6123MS). The amplified

speech signal is passed through the high-pass filter Q1005-

1 (NJM2902V) and low-pass filter Q1005-2 (NJM2902V)

which AM modulate the Tx frequency with speech sig-

nal.

When using the optional headset, the SIDETONE sig-

nal from Q1011 (UMG2) becomes “HIGH”, turning Q1012

(2SC4116GR) on, therefore a portion of the speech signal

applied to the AF power amplifier Q1009 as a monitor

signal.

The carrier signal from the VCO Q1023 (2SC5226)

passes through the buffer amplifier Q1029 (2SC5226) and

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Vertex Standard VXA-150 Manuel de service Page 11

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