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antenna number decoder, and relay coils driver.
The I/O interface circuit receives the input BCD code (A1, A2, A4, A8)
from JP1:4 - JP1:7, via four 4093 type Schmidt inputs and converts them
into 0/+5V logic levels (*A1...*A8) on pins 10, 11, 4, and 3 of U1. The RDY
output signal is buffered via 2003 Darlington arrays (U9B,U9C). See Fig.4-1.
The antenna changes founding register is based on the 4063 type 4 - bit
magnitude comparator (U4). It continuously compares the parallel input BCD
code *A1, *A2, *A4, *A8 (antenna number command) on pins 9, 11, 14, 1
with the currently selected antenna number on pins 10, 12, 13, 15 passed
from the 4042 type quad clocked D - latch. If a difference is found, the
comparator generates a low clock pulse on pin 6 (A=B) which is for-
warded to the D - latch in order to transfer and register the new antenna
number. Every clock pulse is 150ms extended via the 4047 type monostable
(U7) in order to allow the electromagnetic actuators to execute the re-
ceived command. This pulse may be additionaly delayed if RF power is de-
tected at the same time (via the RF signal detector TA/D1, U5A voltage
comparator and U6 logic), until the RF disappears. In such a case the RDY
signal is tied to low via U9C for the period when the input and output
antenna numbers are not matching.
The antenna number decoder inputs are selectively connected to the nor-
mal or inverted D - latch outputs. Selection is done via four jumpers (Code
Levels). The 4028 type BCD to decimal decoder is used (U3) to convert the
antenna number from 4 - bit parallel BCD code into 1 out of 10 antennas
selection.
The relay coils driver consists of U8, U9, and Q1. The first coil ends of all
electromagnetic actuators are fed in parallel from +27V through the tran-
sistor Q1 and/or the resistor R12. The selected antenna output ties down
the second end of the respective coil in order to switch on the actuator.
Meanwhile the transistor Q1 is being saturated for 150ms via the *UP signal
derived from the monostable. In this way full voltage is applied across the
newly switched coil until the actuator pulls in. After the switching, Q1 cuts
off, so R12 reduces the coil heat in settled condition.
The power supply from the control unit is fed to the antenna switch via
JP1:1 (+27V) and JP1:3 (27V return and GND). The consumption is less
than 150mA.
