2-28
2.8 ANT COUP (Antenna Coupler)
1. General
AT-1503 is tunable to an antenna length from 6 m to 15 m in a frequency range of 1.6
MHz to 27.5 MHz. U8 (MPU) starts the automatic tuning (matching) with "TUNE" sig-
nal from the main unit and the result of the matching is sent to the CPU in the main unit
by H and L levels of BUSY signal.
The matching is practiced by a L-type matching circuit and SWR in the matched condi-
tion is less than 2.0 (input impedance: 50
Ω
).
When the SWR has been adjusted to less than 1.5 in a frequency band, the matching data
is stored in the internal RAM of U8. The data is referred when the matching in the fre-
quency band is executed again, thus leading to a quicker matching operation (maximum
time: 15 sec). The matching data is held for about a week by a backup capacitor C42
(1F).
When SWR is larger than 2.0 or it takes longer than 15 sec for a matching, a signal
TUNE ERROR turns ON relays K3 to K12 that bypass the matching coils, thus prevent-
ing the coils to be burnt out.
An optional dummy antenna (10
Ω
+ 250 pF, 100 W) can be built in for the purpose of
maintenance work.
AT-1503 itself is provided with self-check function. Connect J1 to "SELF TEST" and
depress S1 "TUNE", then the self-check automatically starts (see chapter 5).
-3 dB ATT
U1
Q1
U2
U5 1/2
CR2CR1 CR3 CR4
T1 T2
TP2
TP3
TP5
A/D
COUNTER
VrVf
Freq.
Phase
V SWR
P22
TP4
P63
P27
3: TUNE
4: BUSY
6: THROU
J1
TUNE
SELF TEST
TUNE
P51
P56
P50
P53
P57
S1
U8
Y1
(4 MHz)
Voo
C42 (1F)
+5 V
(HD63B01Y0E76P)
K3
K2
K1
K13
K4
K14 K15 K21
K22
K12K11
50 pF
20 pF
2400 pF 1200 pF
0.1
µ
H 0.2
µ
H 25.6
µ
H 51.2
µ
H
U9
K3 to 10
P30
:
P37
U10
K11 to 12
K14 to 19
U11
K20 to 22
K 1, 2, 13
P10
:
P17
P40
:
P47
ANT
TB4
TX ON/RX OUT
TB1
TB2
1: +12 V
2: GND
7: DUMMY
TB3
GND
DRIVER
DRIVER
DRIVER
Cs
MPU
ROM
RAM
CPU
I/O
Back up
Capacitance and Reactance in matching circuit (Matching Data)
Coil: 0.1, 0.2, 0.4, 0.8, 1.6, 3.2, 6.4, 12.8, 25.6, 51.2
µ
H
Capacitor: 2400, 1200, 600, 300, 150, 75, 41, 22 pF
Antenna Shunted Capacitor: fixed to 50 pF
Figure 2-23 Block Diagram of AT-1503
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