Wood and Douglas ST500 Manuel utilisateur
ST500
TRANSMITTER
TECHNICAL MANUAL
(1891 1210)
©Copyright Wood & Douglas Ltd 1998
version: 1.0
issue: November 1998
LATTICE HOUSE
BAUGHURST ROAD
TADLEY
HAMPSHIRE
UK RG26 5LP
Tel: +44 (0)118 981 1444 Fax:+44 (0)118 981 1567
1.0/November 1998 1891 1210
Contents
Section 1
An overview .................................................5
1.1 GENERAL DESCRIPTION ...................................6
Section 2
Operation ...................................................7
2.1 USER CONNECTIONS ......................................7
Section 3
Technical description .........................................9
3.1 POWER SUPPLY ..........................................9
3.2 INPUT INTERFACE .........................................9
3.3 MODULATION STAGE ......................................9
3.4 RADIO FREQUENCY STAGE ................................10
3.5 FREQUENCY PROGRAMMING ..............................14
Section 4
Technical specifications ......................................19
DRAWINGS
WS1494/XX7 GENERAL ARRANGEMENT FOR ST500
WD1632/001 CIRCUIT DIAGRAM FOR ST500
WD1632/XX2 COMPONENT OVERLAY FOR ST500 (Sheet 1 of 3)
WD1632/XX2 COMPONENT OVERLAY FOR ST500 (Sheet 2 of 3)
WD1632/XX2 COMPONENT OVERLAY FOR ST500 (Sheet 3 of 3)
C WD632 00 ITEM LIST FOR LEADED COMPONENTS FOR ST500
ASM163200 ITEMLISTFORSURFACEMOUNT COMPONENTS FOR
ST500
1891 1210 1.0/November 1998
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1.0/November 1998 1891 1210
Section 1
An overview
Wood & Douglas are an independent UK company dedicated to the design and
manufacture ofhighqualityRFdesignsfor the telemetry,security,broadcast and video
markets world-wide.
The information given in this manual is Copyright Wood & Douglas and is provided to
the original purchaser for the purposes of operation and routine maintenance. The
contentsofthis manual must not be disclosed to any third party, nor may the purchaser
make additional copies of the manual or store the information given on any electronic
retrieval or mass storage system.
The company reserves the right to amend or change specifications of its products
without prior notice in accordance with the company policy of continued product
improvement.
NOTE:
This device complies with Part 15 of the FCC Rules.
Operation is subject to the condition that this device does not cause harmful
interference.
The unit is labelled with a serial number label as shown below:
ST500 31 980912345
FCC ID ABCST500 CECE
where: 990912345 is the serial number of the unit containing the date code for
September 1998
ABC is the Wood & Douglas Ltd FCC code
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1891 1210 1.0/November 1998
1.1 GENERAL DESCRIPTION
The ST500 can be configured for analogue or digital operation and is available in the
frequency range of 405 - 470MHz with a 12.5kHz channel spacing.
The transmitter requires a nominal 12 volt DC supply connected via PL7. However
the unit will function correctly within the limits of +6.0V to +14.0V. The output power
of the transmitter is normally preset to 100mW nominal.
The ST500 is intended to fit into OEM equipment housing by means of the three
connectors which protrude through the base of the unit.
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1.0/November 1998 1891 1210
Section 2
Operation
2.1 USER CONNECTIONS
Connection to the ST500 transmitter is made via three headers, PL1, PL2 and PL3,
which plug directly into the user's own equipment. The location of these connectors is
shown in the General Arrangement drawing given at the back of this manual.
The details of these three connectors are detailed below:
PIN NAME FUNCTION REMARKS
10V 0 volts common ground
2bTbXbEtransmit enable o/c = transmitter disabled
LOW <+0.8V = transmitter enabled
1KÙnom. internal pull-up to +Vin
3DIGITAL I/P data input 0/+3V to 0/+12V, DC-coupled
4ANALOGUE I/P data input 300mV to 5V p-p, AC-coupled
5+5V O/P +5V supply output 50mA max. current drain
6RS232 I/P serial programming
input If not used leave un-connected or ground.
(refer to section 3.5 for details)
70V 0 volts common ground
8RB1 parallel frequency
select internal pull-up to +5V, active low
(refer to section 3.5.4 for details)
9RB2
10 RB3
Connector PL1 pin detail
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1891 1210 1.0/November 1998
PIN NAME FUNCTION REMARKS
10V 0 volts common ground
2RF O/P RF output 50 ohms output
30V 0 volts common ground
Connector PL2 pin detail
PIN NAME FUNCTION REMARKS
1+VIN positive supply +6.0V to +14.0V
20V 0 volts common ground
Connector PL3 pin detail
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1.0/November 1998 1891 1210
Section 3
Technical description
Refer to the circuit diagram WD1632 at the rear of this manual.
3.1 POWER SUPPLY
DC power is connected to the transmitter module via PL3. The positive side of the supply
is fed to TR2 which acts as a series switch; when PL1 pin 2 is connected to 0V to enable
the transmitter then base current flows to TR2 via D6 and R54 and turns TR2 on. The
output from the collector of TR2 (‘+Vraw’) is fed to dual operational amplifier IC4, to TR3
collector (via chokes L5 and L6) and also to voltage regulator IC2. This regulator provides
a stable output of nominally +5V which is used to power all the remaining sections of the
transmitter (apart from IC7) either directly or via R-C decoupling networks.
3.2 INPUT INTERFACE
When the transmitter is to be used with an analogue modulation input then this input is fed
from PL1 pin 4 via R2 and C2 to RV1 in the feedback network around IC1a. RV1 acts as
an analogue gain control.
When the transmitter is to be used with a digital modulation input then this input is fed
from PL1 pin 3 via R1 to RV1 in the feedback network around IC1a. RV1 is set mid-way in
this application such that it has no effect; IC1a then functions as a comparator and
produces an output which swings between approximately +0.7V and +4.3V depending on
whether the digital input is low or high. These output levels are well-defined and result in
the modulation level being independent of the logic levels at the input to the transmitter.
3.3 MODULATION STAGE
The output from IC1a is fed to a low-pass filter built around IC1b. This restricts the
modulation bandwidth such that adjacent channel power levels are kept within
specification.
The output from IC1b is fed via R24 and RV2 to RV3 and R28. (C16 adds a further low-
pass filter stage at R24.) The modulation signal at the junction of RV2 and RV3 is fed to
the modulation input of the TCXO U1. The wiper of RV3 is connected via R31 to the
varicap diode D2 in the UHF oscillator.
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1891 1210 1.0/November 1998
RV2 is connected as a variable resistor and consequently controls the amplitude of the
modulation signal to both oscillators; RV2 therefore sets the overall frequency deviation of
the transmitter.
RV3 controls the amplitude of the modulation signal to only the UHF oscillator. This
arrangement constitutes ‘dual-point modulation’; the modulation applied to the UHF
oscillator is only effective outside the bandwidth of the frequency control loop while that
applied to the TCXO is effective within this bandwidth. RV3 thus functions as a ‘deviation
balance’ control and is adjusted such that the overall modulation response is flat across its
full frequency range.
R28 is provided so that there is no significant change in the DC level fed to the modulation
input of the TCXO as RV2 is adjusted. (A DC shift would cause a corresponding shift in
the transmitter frequency.) In contrast, the DC voltage fed to the modulation input of the
UHF oscillator is allowed to change as RV3 is adjusted since this has no effect on the
mean transmitter frequency.
3.4 RADIO FREQUENCY STAGE
TR5 acts as a UHF oscillator whose frequency is determined primarily by L8, D3, D4 and
trimmer C32. D3 and D4 are varicap diodes and allow the oscillator to be tuned by means
of a DC voltage which is fed to the diodes via L9. Trimmer C32 provides coarse tuning of
the oscillator frequency.
Varicap diode D2 is also loosely coupled into the oscillator circuit via C26 and provides a
means of frequency-modulating the oscillator.
The output from the oscillator is developed across R42 at the collector of TR5 and is fed
via C40 to buffer amplifier IC5. This amplifier provides an increased output level while
isolating the oscillator from the rest of the circuit. The output from IC5 is fed through a
low-pass filter (C45, L12 and C48); the output from this filter is fed to the input of the
frequency synthesiser IC6 and also to buffer amplifier IC7.
Frequency synthesiser IC6 incorporates two programmable frequency dividers and an
edge-triggered phase comparator which is driven by the outputs of the two frequency
dividers. The division ratios are controlled by means of serial data generated by
microprocessor IC3. The filtered output from buffer amplifier IC5 is fed via C47 to the
input of one of the frequency divders at pin 8; the other input at pin 1 is driven by the
output of TCXO U1 via C28 and R33. The TCXO provides a reference frequency which is
very stable across the operating temperature range of the transmitter.
The phase comparator output from IC6 appears at pin 5 and is fed via R44 and R41 to L9
in the UHF oscillator. This completes the control loop and IC6 is thus able to control the
frequency of the UHF oscillator. R47 and C44 determine the dynamic behaviour of the
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