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4 CHANNEL AND TONE FREQUENCY PROGRAMMING
TecHelp can be supplied by your dealer, distributor or by contacting RF Technology
directly.
Function
dc power
Channel Select
RS232 Data
600 Ω Line
150 Ω / Hybrid
Direct PTT input
T/R Relay driver output
Sub-Audible Tone Input
High-Z Audio Input
External ALC input
Table 3: Pin connections and explanations for the main 25-pin, D
connector.
5
Circuit Description
The following descriptions should be read as an aid to understanding the block and
schematic diagrams given in the appendix of this manual.
5.1
VCO Section
The Voltage Controlled Oscillator uses a junction FET which oscillates at the
required transmitter output frequency. A varactor diode is used by the PLL circuit to
keep the oscillator on the desired frequency. Transistor Q20 is used as an active
filter to reduce the noise on the oscillator supply voltage. The VCO is keyed ON by
the microcontroller through Q10. It is keyed ON when any of the PTT inputs are
active and OFF at all other times.
RF Technology T220
Signal
Pins
+12 Vdc
1, 14
-12 Vdc
13, 25
1
21
2
9
4
22
8
10
10
23
20
11
40
24
80
12
In
15
Out
2
High
20
Low
6
7
19
3
16
+
5
18
+
4
-
17
8
Specification
+11.4 to 16 Vdc
BCD Coded
0 = Open Circuit
or 0 Vdc
1 = +5 to +16 Vdc
Test and Programming use
9600, 8 data 2 stop bits
Transformer
Isolated
Balanced 0dBm Output
Ground to key PTT
Open collector, 250m /30V
>10k Ω , AC coupled
(1-250Hz)
>10k Ω , AC coupled
(10Hz-3kHz)
<0.5V/1mA to obtain
>30dB attenuation, O/C
for maximum power
Page 9
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