Specifications

amplifies to 0.5W and Q503 amplifies to 3W(SD-161, SD-164) or 6W(SD-171, SD-174) and

then matched to 50 Ohms using the L.C. network or strip line, thereby reducing the harmonics

by -30 dB.

LOW PASS FILTER

L7, L8, L9, C36, C37, C38 and C39 are the 7th order Chebyshev low pass filter. Unwanted

harmonics are reduced by -70 dBc.

ANTENNA SWITCH

When transmitting, the diodes D3 and D5 are forward biased to enable to make an RF path to

the antenna. D5 is shorted to ground to block the RF signal to the front-end. In receive, the

diodes, D3 and D5, are reverse biased to pass the signal from the antenna through L10 and

C61 to the front-end without signal loss.

AUTOMATIC CURRENT CONTROL (ACC) CIRCUITS

The ACC circuit consists of R63, variable resistor RV4, IC5(B) and transistors Q11 and Q12.

The supplied current to the P.A. block is monitored by the voltage difference on R63 (0.1 Ohm).

If the current varies by RF power output or other reasons, it produces a voltage difference on

R63 and then IC5A outputs a bias voltage to Q19 in proportion to that difference. The adjusted

value of Q15 output by RV4 is compared with the reference voltage in IC5B and then a

differential voltage at the output of IC5B is passed to Q12 and Q11 which controls the bias

voltage of the P.A. module to maintain a constant power output to the antenna. RV4 is used to

adjust the RF power level.

4.3.3. RECEIVER

FRONT-END

The front-end block consist of two band pass filters and a low noise amplifier (LNA). The Band

pass filter is used for elimination of image frequency and impedance matching and the LNA is

used to amplify weak RF signals without any increase of noise. The received signal comes from

the antenna, then is input into a band pass filter of the front-end block with C601through C610,

L601 through L604 at UHF and C622 through C608, L607 through L604 at VHF, and is coupled