RF Technology T220 User manual

Eclipse Series
RF Technology
[e-mail]
SEPTEMBER 2003 Revision 2
T220 Transmitter
Operation and Maintenance Manual
This manual is produced by RF Technology Pty Ltd
10/8 Leighton Place, Hornsby 2077 Australia
Copyright © 2001 RF Technology Pty Ltd

Page 2 RF Technology T220
CONTENTS CONTENTS
Contents
1Operating Instructions 5
1.1 Front Panel Controls and Indicators 5
1.1.1 PTT 5
1.1.2 Line 5
1.1.3PWR LED 6
1.1.4 TX LED 6
1.1.5 ALARM LED 6
1.1.6 ALC LED 6
1.1.7 REF LED 7
1.1.8 TEST MIC. 7
2Transmitter Internal Jumper Options 7
2.1 JP2: EPROM type 7
2.2 JP3: Dc Loop PTT 7
2.3 JP4: Audio Input Source 7
2.4 JP5: 600¿ Termination 8
2.5 JP6: Input Level Attenuation 8
2.6 JP7: Audio Response 8
2.7 JP8: Sub-audible Tone source 8
2.8 JP9/10/11: dc Loop Configuration 8
2.9 JP16: Direct Digital Input (Rev 4 or Higher) 9
2.10
JP17: Bypass Low Pass filter (Rev 4 or Higher)
9
2.11 JP19: Alarm Output (Rev 4 or Higher) 9
2.12 JP22: Use Tone- as a Direct Digital Input (Rev 4 or Higher) 10
2.13 JP23: Connection of DMTX Board (Rev 4 or Higher) 10
3Transmitter I/O Connections 11
3.1 25 Pin Connector 11
3.2 Rear Panel Connectors 11
4Channel and Tone Frequency Programming 13
5Circuit Description 13
5.1 VCO Section 13
5.2 PLL Section 13
5.3 Power Amplifier 14
5.4 Temperature Protection 14
5.5 600Ωline Input 14
5.6 Direct Coupled Audio Input 15
5.7 Local Microphone Input 15
5.8 CTCSS and Tone Filter 15
5.9 Audio Signal Processing 16
5.10 PTT and DC Remote Control 16
5.11 Microprocessor Controller 17
5.12 Voltage Regulator 18

RF Technology T220 Page 3
CONTENTS CONTENTS
6Field Alignment Procedure 18
6.1 Standard Test Conditions 18
6.2
VCO Alignment
19
6.3 TCXO Calibration 19
6.4 Modulation Balance 19
6.5 Tone Deviation 20
6.6 Deviation 20
6.7 Line Input Level 20
6.8 Output Power 21
7Specifications 21
7.1 Overall Description 21
7.1.1 Channel Capacity 21
7.1.2 CTCSS 21
7.1.3
Channel Programming
22
7.1.4 Channel Selection 22
7.1.5 Microprocessor 22
7.2 Physical Configuration 22
7.3 Front Panel Controls, Indicators and Test Points 22
7.3.1 Controls 22
7.3.2 Indicators 22
7.3.3 Test Points 23
7.4 Electrical Specifications 23
7.4.1 Power Requirements 23
7.4.2 Frequency Range and Channel Spacing 23
7.4.3 Frequency Synthesizer Step Size 23
7.4.4 Frequency Stability 23
7.4.5 Number of Channels 23
7.4.6 Antenna Impedance 24
7.4.7 Output Power 24
7.4.8
Transmit Duty Cycle
24
7.4.9 Spurious and Harmonics 24
7.4.10 Carrier and Modulation Attack Time 24
7.4.11 Modulation 24
7.4.12 Distortion 24
7.4.13 Residual Modulation and Noise 24
7.4.14 600ΩLine Input Sensitivity 24
7.4.15 HI-Z Input 25
7.4.16 Test Microphone Input 25
7.4.17 External Tone Input 25
7.4.18 External ALC Input 25
7.4.19 T/R Relay Driver 25
7.4.20 Channel Select Input / Output 25
7.4.21 DC Remote Keying 25
7.4.22 Programmable No-Tone Period 26
7.4.23 Firmware Timers 26

Page 4 RF Technology T220
CONTENTS CONTENTS
7.4.24 CTCSS 26
7.5 Connectors 26
7.5.1 Antenna Connector 26
7.5.2 Power and I/O Connector 28
7.5.3 Test Connector 28
AEngineering Diagrams 28
A.1 Block Diagram 28
A.2 Circuit Diagrams 28
A.3 Component Overlay Diagrams 29
BParts List 30

RF Technology T220 Page 5
1OPERATING INSTRUCTIONS
1Operating Instructions
1.1 Front Panel Controls and Indicators
1.1.1 PTT
A front-panel push-to-talk (PTT) button is provided to facilitate bench and field tests
and adjustments. The button is a momentary action type. When keyed, audio from the
line input is disabled so that a carrier with subtone is transmitted. The front-panel
microphone input is not enabled in this mode, but it is enabled when the PTT line on
that socket is pulled to ground.
1.1.2 Line
The LINE trimpot is accessible by means of a small screwdriver from the front panel of
the module. It is used to set the correct sensitivity of the line and direct audio inputs. It
is factory preset to give 60% of rated deviation with an input of -6dBm (388mV RMS)
at 1kHz. The level may be measured between pins 6 and 1 on the test socket. The
adjustment range is approximately -30dBm to +10dBm.
An internal jumper provides a coarse adjustment step of 20dB. Between the jumper and
the trimpot, a wide range of input levels may be accommodated.
WARNING
Changes or modifications not expressly approved by
RF Technology could void your authority to operate this
equipment. Specifications may vary from those given in
this document in accordance with requirements of local
authorities. RF Technology equipment is subject to
continual improvement and RF Technology reserves the
right to change performance and specification without
further notice.

Page 6 RF Technology T220
1.1.3 PWR LED 1 OPERATING INSTRUCTIONS
LED Flash Cadence Fault Condition
5 flashes, pause Synthesizer unlocked
4 flashes, pause Tuning voltage out of range
3 flashes, pause Low forward power
2 flashes, pause High reverse (reflected) power
1 flash, pause Low dc supply voltage
LED ON continuously
Transmitter timed out
Table 1: Interpretations of LED flash cadence
Indication Fault Condition
Flashing, 5 per second Synthesizer unlocked
Flashing, 4 per second Tuning voltage outside correct range
Flashing, 2 per second Low forward power
Flashing, 1 per second High reverse power
Continuous dc supply voltage low or high
Table 2: Interpretations of LED flash speed, for early models
1.1.3 POWER LED
The Power LED shows that the dc supply is connected to the receiver.
1.1.4 TX LED
The TX LED illuminates when the transmitter is keyed. It will not illuminate (and an
ALARM cadence will be shown) if the synthesizer becomes unlocked, or the output
amplifier supply is interrupted by the microprocessor.
1.1.5 ALARM LED
The Alarm LED can indicate several fault conditions if they are detected by the self test
program. The alarm indicator shows the highest priority fault present. Transmitters
using software issue 5 and higher use the cadence of the LED flash sequence to indicate
the alarm condition. Refer to table 1. Transmitters using software issue 4 and lower
use the LED flash rate to indicate the alarm condition. Refer to table 2.
1.1.6 ALC LED
The ALC LED indicates that the transmitter output power is being controlled by an
external amplifier through the external ALC input.

RF Technology T220 Page 7
1 OPERATING INSTRUCTIONS 1.1.7 REF LED
1.1.7 REF LED
The REF LED indicates that the synthesizer frequency reference is locked to an external
reference.
1.1.8 TEST MIC.
The TEST MIC. DIN socket is provided for use with a standard mobile or handset
200
Ohm dynamic microphone. The external audio inputs are disabled when the TEST
MIC’S PTT is on.
2Transmitter Internal Jumper Options
In the following subsections an asterisk (*) signifies the standard (Ex-Factory)
configuration of a jumper.
2.1 JP2: EPROM Type
Condition Position
27C256 2-3 *
27C64 1-2
2.2 JP3: Dc Loop PTT
By default, Eclipse exciters can be keyed up by pulling the PTT signal low, or by dc
loop signaling on the audio paid.
This jumper can enable, or disable this second method.
Condition Position
dc loop connected (enabled) 1-2 *
dc loop not connected (bypassed) 2-3
2.3 JP4: Audio Input Source
Either the 600Ωor the high-Z balanced inputs may be selected.
Condition Position
600ΩInput 2-3 *
High-impedance Input 1-2

Page 8 RF Technology T220
2.4 JP5: 600¿ Termination 2 TRANSMITTER INTERNAL JUMPER OPTIONS
2.4 JP5: 600 ¿ Termination
Normally the Line Input is terminated in 600¿ . The 600 ohm termination can be
removed by choosing the alternate position.
Condition Position
600¿ Termination 1-2*
No Termination 2-3
2.5 JP6: Input Level Attenuation
This jumper permits coarse input sensitivity to be set. In the default position, the unit
expects a line level of 0dBm (nominal) at its Line Input. In the alternate position,
levels of +20dBm(nominal) can be accepted.
Condition Position
0dB attenuation 1-2 *
20dB attenuation 2-3
2.6 JP7: Audio Response
Condition Position
750 uSec. pre-emphasis 1-2 *
Flat response 2-3
2.7 JP8: Subaudible Tone Source
Condition Position
Internal CTCSS 1-2, 4-5 *
External input 2-3, 5-6
2.8 JP9/10/11: dc Loop Configuration
DC loop current on the audio
pair, is normally soured externally. The Eclipse exciters
loop the current through an opto-isolator. When the current flows the exciter keys up.
An alternative arrangement is possible. The exciter can source the current and an
external device can provide the dc loop.
These three jumpers select the appropriate mode.
Condition JP9 JP10 JP11
Current Loop Input ON OFF OFF *
12Vd Loop source OFF ON ON

RF Technology T220 Page 9
2.9 JP16: Direct Digital Input 2 TRANSMITTER INTERNAL JUMPER OPTIONS
2.9 JP16: Direct Digital Input (Rev 4 or Higher)
Some trunking controllers have digital encoding schemes which operate to very low
frequencies. The elliptical filter, used as a 250Hz low pass filter in the tone section,
can cause excessive pulse edge distortion of the trunking controller’s digital signals. In
such circumstances, JP16 allows a user to bypass the low ad high pass filters in the tone
input section. See also 2.12 - JP22: If direct tone input is selected, then JP22 should be
removed (open).
Condition Position
Normal Tone Input 1-2*
Direct Tone Input 2-3
2.10 JP17: Bypass Low Pass Filter (Rev 4 or Higher)
Some trunking controllers have digital encoding schemes that require the low pass filter
in the tone input section to be bypassed. JP17 allows this. Normally JP17 is open
circuit. Placing a link across it will bypass the low pass filter.
In conjunction with this change, it sometimes may be necessary, depending upon the
type of trunking controller used, to add a 100K resistor in the place reserved for R157.
2.11 JP19: Alarm Output (Rev 4 or Higher)
The main audio transformer (T1), is connected to the Line IP1 and Line IP4 pins on P3.
These two pins constitute the main audio input for the exciter. The centre taps of the
audio transformer, though, are brought out on Line IP2 and Line IP3. These can be
used as alternate audio inputs for larger signals, or to directly access the dc loop sense
circuitry. JP19 allows an alternate use for Line IP2 (pin 7 of P3). In the alternate
position for JP19, the ALARM signal (the signal that drives the ALARM LED itself) is
connected to pin 7 of P3. The ALARM signal when asserted is low active; when
unasserted, it pulls high to +9.4V through an LED and a 680 ohm resistor.
Condition Position
P3, pin7 connects to centre tap of transformer T1 1-2*
P3, pin 7 connects to ALARM signal 2-3

Page 10 RF Technology T220
2.13 JP23: Connection of DMTX 2 TRANSMITTER INTERNAL JUMPER OPTIONS
2.12 JP22: Use Tone- as a Direct Digital Input (Rev 4 or
Higher)
JP22 is normally shunted with a jumper, which connects Tone- on P3 (pin 18), as the
negative leg of the Tone input pair. Removing this jumper disconnects Tone- from this
path and allows the use of the Tone- pin to be used as a direct digital input. See also
2.9 - JP16: If the jumper is removed, then JP16 should be in the alternative position
(Direct Tone Input)
2.13 JP23: Connection of DMTX Board (Rev 4 or Higher)
When the DMTX board is connected to an exciter, there is provision for digital or audio
modulation of the reference oscillator and VCO. The digital signal is input via the DB9
rear connector and the audio input signal is via the Line inputs on the standard DB25
rear panel connector.
Condition Position
N DMTX board 1-2, 5-6*
DMTX board connected 2-3, 4-5

RF Technology T220 Page 11
3 TRANSMITTER I/O CONNECTIONS 3.1 25 Pin Connector
3Transmitter I/O Connections
3.1 25 Pin Connector
The D-shell 25 pin connector is the main interface to the transmitter. The pin
connections are described in table 3.
Function Signal Pins Specification
DC power +12 Vdc
0 Vdc 1, 14 13, 25 +11.4 to 16 Vdc
Channel Select 1
2
4
8
10
20
40
80
21
9
22
10
23
11
24
12
BCD Coded
0 = Open Circuit
or 0 Vdc
1 = +5 to +16 Vdc
RS232 Data In
Out 15 2
Test and Programming use
9600, 8 data 2 stop bits
600ΩLine High
Low 20 6Transformer Isolated Balanced 0dBm Output
150Ω/ Hybrid 7
19
Direct PTT input 3Ground to key PTT
T/R Relay driver output 16 Open collector, 250m /30V
Sub-Audible Tone Input Tone+ 5>10kΩ, AC coupled
Tone- 18 (1-250Hz)
High-Z Audio Input HiZ+ 4 >10kΩ, AC coupled
HiZ- 17 (10Hz-3kHz)
External ALC input 8 <0.5V/1mA to obtain
>30dB attenuation, O/C
for maximum power
Table 3: Pin connections and explanations for the main 25-pin, D
connector.
3.2 Rear Panel Connectors
The exciter and receiver can be supplied with optional rear panel connectors that bring
out the more important signals available on P1, the rear panel DB25 connector.
Figures 1 and 2 show the rear panel connectors, and Table 4 shows the signals that are
brought out onto spade connectors for these daughter boards. The spade connectors
(2.1 x 0.6 x 7mm) are captive/soldered at the labelled points.

Page 12 RF Technology T220
3.2 Rear Panel Connectors 3 TRANSMITTER I/O CONNECTIONS
Fig 1 Fig 2
RX PCB TX PCB
The Receiver and Transmitter modules plug into the back plane DB25/F connectors
To configure: Solder wire connections between appropriate points.
Receiver
DB25/F RX PCB DESCRIPTION TX PCB Transmitter DB25/F
1, 14 +12V +12V DC SUPPLY +12V 1, 14
2TXD TX Data TXD 2
15 RXD RX Data RXD 15
3COR+ Carrier Operate Sw+ PressToTalk input PTT 3
16 COR- Carrier Operate Sw- Tx/Rx output T/R 16
4TONE Subtone output Hi Z audio input+ AUD+ 4
17 AUDIO Audio output Hi Z audio input- AUD- 17
5AGND Audio Ground Ext tone input+ TONE+ 5
18 DISC Discriminator output Ext tone input- TONE- 18
6LINE+ Line output+ Line input+ LINE+ 6
20 LINE- Line output- Line input- LINE- 20
8EXT SQ Ext Squelch input Auto Level Control ALC 8
13, 25 GND Ground, 0V GND 13, 25
21 BCD 1 Channel select 1’s digit BCD 1 21
9BCD 2 Channel select 1’s digit BCD 2 9
22 BCD 4 Channel select 1’s digit BCD 4 22
10 BCD 8 Channel select 1’s digit BCD 8 10
23 BCD 10 Channel select 10’s digit BCD 10 23
11 BCD 20 Channel select 10’s digit BCD 20 11
24 BCD 40 Channel select 10’s digit BCD 40 24
12 BCD 80 Channel select 10’s digit BCD 80 12
Table 4

RF Technology T220 Page 13
4 CHANNEL and TONE FREQUENCYPROGRAMMING
4
Channel and Tone Frequency Programming
Channel and tone frequency programming is most easily accomplished with RF
Technology TecHelp Software or the Service Monitor 2000 software. This software
can be run on an IBM compatible PC and provides a number of additional useful
facilities. DOS and 32-bit versions are available.
TechHelp allows setting of the adaptive noise squelch threshold, provides a simple
means of calibrating the forward and reverse power detectors, setting the power alarm
preset levels, and enabling transmitter hang time and timeout time limits.
TecHelp/Service Monitor can be supplied by your dealer, distributor or by contacting
RF Technology directly.
5Circuit 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.
The VCO output is amplified and buffered by monolithic amplifiers MA2 and MA3
before being fed to the PLL IC U6.
Amplifiers MA1, MA4 and MA5 increase the VCO output to approximately 4 mW to
drive the power amplifier. MA1 is not switched on until the PLL has locked and had
time to settle. This prevents any momentary off channel transmission when the
transmitter is keyed.
5.2 PLL Section
Temperature compensated crystal oscillator XO1 is the frequency reference source for
the PLL Synthesizer. The frequency stability of XO1 is better than 1 ppm and it can be
synchronized to an external reference for improved stability. External reference option
board 11/9119 is required when using an external reference.
XO1 is frequency modulated by the processed transmit audio signal from U7b. This
extends the modulation capability down to a few Hz for sub-audible tones and digital
squelch codes. A two point modulation scheme is used with the audio also being fed to
the VCO to modulate the higher audio frequencies.

Page 14 RF Technology T220
5.3 Power Amplifier 5 CIRCUIT DESCRIPTION
The 12.8MHz output of XO1 is amplified by Q22 to drive the reference input of the
PLL synthesizer IC U6. This IC is a single chip synthesizer which includes a 1.1 GHz
pre-scaler, programmable divider, reference divider and phase/frequency detector. The
frequency data for U6 is supplied through serial data link by the microprocessor.
The phase detector output signals of U6 are used to control two switched current
sources. The output of the positive and negative sources (Q3 and Q6) produces the
tuning voltage which is smoothed by the loop filter components to bias the VCO
varactor diode D3.
5.3 Power Amplifier
The
4 mW output from the main board connects to the power amplifier board through a
short miniature 50
Ωcoaxial cable.
Q2 on the power amplifier board increases the signal to approximately 200 mW. The
bias current of Q2 is controlled by Q1 and the power leveling circuitry to adjust the
drive to the output module U2.
U2 increases the power to 10--30 watts (depending upon options) before it is fed to the
directional coupler, low pass filter and output connector. The directional coupler
detects the forward and reverse power components and provides proportional dc
voltages which are amplified by U1a and U1b. The forward and reverse voltages from
U1a and U1b are compared to the DC reference voltage from RV1.
The difference is
amplified by U1c, Q3 and Q4.
The resulting control voltage supplies Q2 through R10, R12 and completes the power
leveling control loop.
5.4 Temperature Protection
Thermistor RT1 on the power amplifier board is used to sense the case temperature of
the output module U2. If the case temperature rises above 90 degrees C., the voltage
across RT1 will increase and transistor Q5 will be turned on. This reduces the dc
reference voltage to the power regulator which in turn reduces the outpower by 6-10dB.
5.5 600ΩLine Input
The 600Ωbalanced line input connects to line isolation transformer T1. T1 has two
150Ωprimary windings which are normally connected in series for 600Ω
lines. The
dual primary windings can be used to provide DC loop PTT signaling or a 2/4 wire
hybrid connection. All four leads are available at the rear panel system connector.
The secondary of T1 can be terminated with an internal 600Ω
load through JP5 or left
un-terminated in high impedance applications.

RF Technology T220 Page 15
5 CIRCUIT DESCRIPTION 5.6 Direct Coupled Audio Input
5.6 Direct Coupled Audio Input
A high impedance (10k
Ω) direct AC coupled input is available at the system connector.
The direct coupled input connects to U9a which is configured as a unity gain bridge
amplifier.
The bridge configuration allows audio signal inversion by interchanging the positive
and negative inputs and minimizes ground loop problems. Both inputs should be
connected, with one lead going to the source output pin and the other connected to the
source audio ground.
5.7 Local Microphone Input
The local microphone input is provided for use with a standard low impedance dynamic
microphone.
The microphone output is amplified by U9a before connecting to analog
switch U10a. U10b inverts the local microphone PTT input to switch U10a ON when
the microphone PTT button is pressed. U10a is OFF at all other times.
The local microphone audio has priority over the other inputs. Activation of the local
microphone PTT input switches OFF the audio from the line or direct inputs through
D16 and U10c.
5.8 CTCSS and Tone Filter
The CTCSS encoder module H1, under control of the main microprocessor U13, can
encode all 38 E.I.A.\ tones and (on some models) additional
commonly-used tones.
The tone output of H1 connects to jumper JP8 which is used to select either H1 or
an
external tone source. The selected source is coupled to U9c which is a balanced input
unity gain amplifier. The buffered tone from U9c is fed to 300 Hz low pass filter U7c.
RV3, the tone deviation trimmer, is used to adjust the level of the tone from U7c before
it is combined with the voice audio signal in the summing amplifier U7a.
For some trunking controllers, it is necessary to increase the level of tone signal
generated. For these trunking controllers an extra resistor of value 100K is soldered
into the normally vacant location denoted on the PCB as R157. This increases the gain
from the tone input by a factor of 5.7 (15dBm).
The low pass filter can be bypassed by inserting a link onto Jumper JP17.
Back to back diodes D4 and D5 limit the maximum tone signal amplitude to prevent
excessive tone deviation when external tone sources are used.
The high and low pass filters, and the limiter can all be bypassed by choosing the non
default position for jumper JP16, and. as well, removing the link from JP22. This
connects the TONE - pin of P3 directly into the summing amplifier U7a.

Page 16 RF Technology T220
5.8 Audio Signal Processing 5 CIRCUIT DESCRIPTION
5.9 Audio Signal Processing
Jumper JP4 selects either the line or direct input source. The selected source is then
connected to JP6. JP6 can be removed to provide 20 dB attenuation when the input
level is above 10 dBm to expand the useful range of the line level trimmer RV4. The
wiper of RV4 is coupled to the input of the input amplifier U9d. U9d provides a
voltage gain of ten before connecting to the input of analog switch U10c.
The outputs of U10a and U10c are connected to the frequency response shaping
networks C52, R133 (for 750
µ
s pre-emphasis) and C61, R55 (for flat response). JP7
selects the pre-emphasised or flat response.
The audio signal is further amplified 100 times by U7d. U7d also provides the
symmetrical clipping required to limit the maximum deviation. The output level from
U7d is adjusted by RV1, the deviation adjustment, before being combined with the
tone audio signal in the summing amplifier U7a.
The composite audio from U7a is fed through the 3Khz low pass filter U7b. When the
links on JP23 are in their default state, the filtered audio is coupled to the TCXO
voltage tuning input and the modulation balance trimmer RV2. RV2,
R99 and R98 attenuate the modulation signal before applying it to the VCO via
varactor D3.
When a DMTX board option is required, jumper JP23 allows the audio paths to be re-
routed. The DMTX board provides for an external digital modulation input signal.
When the two links on JP23 are positioned in the middle of the 6 pin header, the audio
from the exciter is passed to the DMTX board via pin 5 of JP5, where the signal is
conditioned and then returned from the DMTX board via pin 2 of JP15, and passed to
the two modulation points.
RV2 adjusts level of the audio used to modulate the VCO. This primarily effects the
deviation of audio frequencies above 500 Hz. RV2 is used to balance the high and
low frequency deviation to obtain a flat frequency response relative to the desired
characteristic.
5.10 PTT and DC Remote Control
Two main PTT inputs are provided. The first, a direct logic level input, is connected
to pin 3 of the system connector. The transmitter can be keyed by applying
a logic
low or ground on pin 3. Pin 3 connects to the PTT logic and microprocessor through
D10.
DC current loop control can be used for remote PTT operation.
The current loop can
be configured by JP9, JP10 and JP11 for use with either a remote free switch or a
remote switched source.

RF Technology T220 Page 17
5CIRCUIT DESCRIPTION 5.11 Microprocessor Controller
Opto-isolator ISO1 is used to isolate the loop current signal from the transmitter PTT
logic. The loop current passes through the input of ISO1 and the output of ISO1
connects to the PTT logic.
A bridge consisting of diodes D6, D8, D9 and D14 ensures correct operation regardless
of the current polarity. Q17 limits the current and D7 limits the voltage input to ISO1.
Any low voltage current source capable of providing 2 mA at 4 V or switching circuit
with less than 4.8kΩloop resistance can be used to switch the DC loop.
The test PTT button on the front panel and the local microphone PTT button will also
key the transmitter. Both of these also mute the line audio input. The microphone line
also enables that audio input.
A DMTX board can also cause the exciter to key up. When a TX (or TTL_TX) signal
is received by the DMTX board, it pulls pin 6 of JP15 low, which, in turn asserts the
PTT_WIRE_OR signal, causing the microprocessor (U13) to key the exciter up.
5.11 Microprocessor Controller
The microprocessor controller circuit uses an single-chip eight bit processor and several
support chips. The processor U13 includes non-volatile EE memory for channel
frequencies, tones, and other information. It also has an asynchronous serial port, a
synchronous serial port and an eight bit analogue to digital converter.
The program is stored in U5, a CMOS EPROM. U4 is an address latch for the low order
address bits. U2 is used to read the channel select lines onto the data bus. U11 is an
address decoder for U5 and U2. U3 is a supervisory chip, which keeps the processor
reset unless the +5 Volt supply is within operating limits. U1 translates the
asynchronous serial port data to standard RS232 levels.
The analogue to digital converter is used to measure the forward and reverse power
,
tuning voltage and dc supply voltage.
If the processor detects that the PTT_WIRE_OR signal is asserted low, it will attempt to
key the exciter up. It will first attempt to key the VCO through Q10, and if the LD pin
goes high, it will switch the 9.2 Volt transmit line through Q14 and Q16. Asserting
Q16 has the effect of also asserting the yellow Tx LED (D12) on the front panel,
enabling the local
25W power amplifier, and causing the T/R Relay output to be pulled
low. D24 is 30 volt zener which protects Q25 from both excessive voltages or reverse
voltages.
Should there be a problem with either the tuning volts, or the battery voltage, the VCO
locking, the forward power, or the reverse power, the microprocessor will assert the
ALARM LED through Q1. Depending on the setting of Jumper JP19, the ALARM
signal can be brought out on pin 7 of P3.

Page 18 RF Technology T220
5.12 Voltage Regulator 5 CIRCUIT DESCRIPTION
5.12 Voltage Regulator
The
dc input voltage is regulated down to 9.4 Vdc by a discrete regulator circuit. The
series pass transistor Q23 is driven by error amplifiers Q8 and Q18. Q9 is used to start
up the regulator and once the circuit turns on, it plays no further part in the operation.
The +5 Volt supply for the logic circuits is provided by an integrated circuit regulator
U14 which is run from the regulated 9.4 Volt supply.
Jumper JP18 is not normally fitted to the board, and is bridged with a 12mil track on the
component side of the board. It is provided so that the 9.4V load can be isolated from
the supply by the service department to aid in fault finding.
Jumpers JP20 and JP21 are also not normally fitted on the board, and are usually
bridged with as12mil track on the component side. They allow U14 to be isolated from
its input, or its output or both.
6Field Alignment Procedure
The procedures given below may be used to align the transmitter in the field. Normally,
alignment is only required when changing operating frequencies, or after component
replacement.
The procedures below do not constitute an exhaustive test or a complete alignment of
the module, but if successfully carried out are adequate in most circumstances.
TCXO calibration may be periodically required owing to normal quartz crystal aging. A
drift of 1ppm/year is to be expected.
Each alignment phase assumes that the preceding phase has been successfully carried
out, or at least that the module is already in properly aligned state with respect to
preceding conditions.
6.1 Standard Test Condition
The following equipment and conditions are assumed unless stated otherwise:
•AF signal generator with 600Ωimpedance, 150--3000Hz frequency range, with
level set to 387mV RMS.
•
Power supply set to 13.8Vdc, with a current capability of >5A.
•RF 50Ωload, 30W rated, return loss <-20dB.
•Jumpers set to factory default positions.

RF Technology T220 Page 19
6 Field Alignment Procedure 6.2 VCO Alignment
6.2 VCO Alignment
1. Select a channel at the centre frequency (half way between the highest and lowest
frequencies for the model in question).
2. Disconnect the Audio input (no signal input).
3. Key the PTT line.
4. Measure the voltage between pins 9 and 1 of the test socket (TUNEV), and adjust
C99 to obtain 4.5±0.2V, while the TX LED is ON and the ALARM LED is OFF.
6.3 TCXO Calibration
1. Select a channel at the centre frequency (half way between the highest and lowest
frequencies for the model in question).
2. Disconnect the Audio input (no signal input).
3. Key the PTT line.
4.
Measure the carrier frequency at the output connector, and adjust XO1 until
the
correct carrier frequency is measured, ±50Hz.
6.4 Modulation Balance
1.
Set RV3 fully CCW (subtone off).
2.
Set RV1 fully CW (maximum deviation)
3. Set RV2 mid-position
4. Set JP7 for flat response
5. Key the transmitter on
6. Set the audio input to 150Hz, 0dBm.
7. Measure deviation and adjust RV4 (line Level) for a deviation of 5kHz (2.5kHz
for narrow band transmitters).
8. Set the audio input to 1.5kHz, 0dBm.
9.
Adjust RV2 (Mod. Bal.) for a deviation of 5kHz (2.5kHz for narrow band
transmitters).

Page 20 RF Technology T220
6.5 Tone Deviation 6 FIELD ALIGNMENT PROCEDURE
10. Repeat steps 6-9 until balance is achieved.
11. Key the transmitter off.
12. Return JP7 to its correct setting.
13. Carry out the Deviation (section 6.6) and Tone Deviation (section 6.5) alignment
procedures.
6.5 Tone Deviation
1. Remove the audio input.
2. Key the transmitter on.
3.
Adjust RV3 for the desired deviation in the range 0-
1kHz.1
If subtone
(CTCSS) coding is not to be used, adjust RV3 fully CCW.
6.6 Deviation
1.
Set RV4 (Line Level) fully clockwise (CW).
2. Set the audio to 1kHz, 0dBm, on the line input.
3. Key the transmitter on..
4. Adjust RV1 (Set Max. Deviation) for a deviation of 2.5kHz.
5. Key the transmitter off.
6.
Carry out the Line Input Level alignment procedure (section 6.7)
6.7 Line Input Level
1. Set the audio to 1kHz, 0dBm, on the line input, or use the actual signal to be
transmitted.
2. Key the transmitter on.
3. Adjust RV4 (line level) for 60% of system deviation (1.5kHz )
___________________
1
The factory default is 500Hz for wide band (5kHz maximum deviation) and 250Hz for narrow band
channels.