Kenwood NXR-5700 Service Manual Download

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1-10 (No.RA033<Rev.001>)

2.6

CIRCUIT DESCRIPTION

2.6.1 Outline

The NXR-5700 is a VHF repeater operating in the 136~174MHz frequency range. Transmit RF power range is 0.5W to 25W adjust-
able. Receiver's frontend BPFs are electrically adjusted in the factory.

2.6.2 Transmitter unit

The transmitter unit (XC1-065 A/3) consists of the following circuit.

(1) 10MHz Internal frequency reference signal circuit
(2) Internal/external reference signal circuit
(3) Internal frequency reference 19.2MHz PLL circuit
(4) Transmitter Modulation 16.8MHz PLL circuit
(5) Transmitter main PLL circuit
(6) Driver amplifier circuit
(7) Modulation level adjustment circuit
(8) AVR circuit
(9) Other circuits

2.6.2.1

10MHz internal frequency reference signal circuit

The internal frequency reference is generated by the 20MHz VCTCXO of X601. Oscillation frequency is adjusted by IC605, IC607 and
IC608. If even one of X601, IC607 or IC608 is replaced, VCTCXO's frequency must be adjusted again.
After the 20MHz frequency reference signal is amplified by IC604, it is divided by IC602. 10MHz signal is distributed to TX unit. In
addition, this 10MHz signal can be distributed to "REF OUT" terminal.
The 10MHz internal frequency reference signal circuit consists of IC602, IC604, IC605, IC607, IC608, D605, D606 and X601.

Fig.1 Internal reference circuit

2.6.2.2

Internal/external reference signal circuit

The internal/external reference circuit automatically switches signals used as reference signals among the 10MHz internal reference
signal, the 10MHz external reference signal and internal 10MHz OCXO (optional) unit.
If no OCXO unit is installed, and there is no external reference signal, the 10MHz internal reference signal is selected as the reference
signal. This reference signal is fed to "REF OUT" terminal.
If the OCXO unit is installed and there is no external reference signal, the 10MHz OCXO unit is selected as the reference signal. This
reference signal is fed to "REF OUT" terminal.
If an external reference signal (at CN502/ 10MHz/ 0~+10dBm) is input, the external reference signal is selected as the reference signal
irrespective of the 10MHz internal reference signal or OCXO unit. This reference signal is fed to "REF OUT" terminal.
"REF OUT" terminal is CN601. The output level is more than + 5dBm (Zout = 50ohm).
If the repeater is operating with NXR-x00 series for trunking mode, if there is no external reference signal and the OCXO unit is not
installed, Q605, Q606, Q609, IC603 and IC606 are not activated. Therefore, there is no output of the reference signal from the "REF
OUT" terminal.
The input impedance of external reference circuit is controlled by Q514. If "REF_TERM" signal is high, the input impedance is low
(approx. 50ohm). "REF_TERM" signal is low, the input impedance is high (more than 1kohm).
The internal/external reference circuit consists of D501, D502, D503, D504, D507, D508, D509, D510, D511, D601, D602, D603,
D604, D607, D608, D609, D610, D611, D612, D613, D614, D615, Q502, Q503, Q504, Q505, Q506, Q507, Q508, Q509, Q510, Q511,
Q512, Q513, Q514, Q515, Q601, Q602, Q603, Q604, Q605, Q606, Q607, Q608, Q609, Q610, Q611, IC501, IC502, IC503, IC504,
IC505, IC601, IC603 and IC606.