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CIRCUIT DESCRIPTION
1. Receiver System
1) F ilter U nit
a. HF Antenna Input
SA501 and R527 are installed in the input part of HF antenna terminal as the
countermeasure against the thunder.
The electric charge of HF antenna is discharged at R527, and when the voltage
becomes over about 300V, the gap of SA501 is discharged so that the receiving
input circuit is protected.
The input signal from HF antenna is passed through the transmission/reception
selecting relay RL513. The followings are prevented in LPF consisting of 1525,
L526, C580, C581 and C582: 2m band image receiving, passing through the First
IF (71,75MHz) and leaking of the first local oscillating frequency (72~130MHz) to
the antenna terminal.
b. 50MHz Antenna Input
The receiving signal from the antenna of 50MHz band is passed through the LPF
for transmission/reception and passed through the transmitting power detection
circuit, then led to transmission/reception switching circuit consisting of D508 and
D509, and to HPF. The signal is amplified about 8dB in Q503. Because the space
noise in 50MHz band is less than it in HF band, its exclusive receiving preamplifier
is equipped to get high sensitivity.
The receiving signal of 50MHz or HF is selected in RL514, then after passing
through the attenuator circuit (ON/OFF) of about 20dB consisting of RL515, R528
and R531 the signal is led to the Main unit.
2) Main U nit
a. Front End
The receiving signal output from Filter Unit is fed to Main unit through CN2. •
HPF, consisting of L19, L20, C47, C48, C49, C50, C51 and C52, eliminates the
strong radio signal of MW band of 1.6MHz or below. In case of receiving the
signal of 1.6MHz or below, the sensitivity is controlled by the attenuator in R37 and
BPF1, also the signal is separated into 1.6MHz, over or below.
5 BPF units consists of 9 filters. Each filter covers the following frequency range.
The frequency of 2.5MHz or more consists of Chebyshev BPF, and under 2.5MHz
frequency band is LPF. Two BPF's are installed on the same unit. Not to be
influenced so much, the distant frequency band BPF’s are combined.
-
1.6MHz BPF1
1.G -
2..5MH2
BPF2
1.8MHz
2.5 - 4.5MHz BPF3 3.5MHz
4.5 - 7.5 MHz
BPF4
7MHz
7.5 - 10.5MHz
BPF1 10MHz
10.5-
14.5MHz
BPF2 14MHz
14.5- 21.5MHz BPF3 18, 21 MHz
21.5- 30MHz
BPF4
24, 2BMHz
50 - 54MHz
BPF5
50MHz
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