Broadcast Warehouse TX 25/50 User manual

Broadcast Warehouse
TX 25/50 FM BROADCAST TRANSMITTER
No part of this manual may be re-produced in any form without prior written permission from Broadcast Warehouse.
The information and specifications contained in this document is subject to change at any time without notice.
Copyright 2001 Broadcast Warehouse
For the latest contact information for Broadcast Warehouse please visit our website at,
www.broadcastwarehouse.com
Technical manual

TX25/50 FM Transmitter technical manual page 2
CONTENTS
1. Introduction
1.1 TX FM Transmitter
1.2 Safety
1.3 Front And Rear Panels
1.4 Control And Monitor LCD
2. Installation And Setup
2.1 Frequency Setup
2.2 R.F. Power Setup
2.3 Alarms
2.4 RS232 Control & Monitoring
2.41 RS232 Interface board
2.42 Windows application
2.43 Terminal control
2.5 Modes Of Operation
2.51 A guide to the jumpers
2.52 Multiplex / Broadband Input
2.53 Stereo With Limiters
2.54 Stereo With Limiters Disabled
2.55 Mono From Two Channels
2.56 Mono From One Channel
2.6 Other Setup Considerations
3. Technical data
3.1 Specifications
3.2 Circuit Description
3.3 Block Diagram
3.4 Internal Wiring / Case Overview
3.5 Schematics
3.51 LCD Control Section
3.52 Power Amplifier Section
3.53 All In One Exciter Section
3.531 Limiter Section
3.532 Coder Section
3.533 Exciter Section
3.6 Parts List
3.61 LCD Control board parts list
3.62 Power Amplifier board parts list
3.63 Combo board parts list

TX25/50 FM Transmitter technical manual page 3
Introduction
1.1 TX 25/50 FM TRANSMITTER
The Broadcast Warehouse TX 25/50 is a high specification FM broadcast transmitter. Its broadband “no-tune”
design allows 87.5-108 Mhz operation from internal direct reading rotary switches or the front panel LCD frequen-
cy control system if enabled. Digital PWM techniques provide an easily adjustable and accurate automatic level
controlled R.F. output of the Mos-Fet power amplifier stage.
R.F., Audio and other parameters are shown on the LCD graphics display. This display offers a very easy method
of transmitter parameter monitoring and a new level of ease for setup and installation, with metering accuracy nor-
mally only found on expensive test equipment. Local and remote personal computer control and metering are
achievable via the innovative dual method RS232 interface.
The FM modulator section employs a dual speed “virtual VFO” system for extremely low audio distortion and
excellent stereo performance.
A built in high specification stereo encoder provides crystal clear stereo sound and combined with the internal lim-
iter a fully compliant “plug and play” all in one low power broadcast transmitter.
For future compatibility all settings are switchable with on board jumpers. The stereo and/or limiter settings can be
switched in and out to suit the requirements of any external broadcast equipment you may have now and in the
future.
The lightweight universal mains input design ensures a high reliability efficient design compatabile with any mains
system in the world.

TX25/50 FM Transmitter technical manual page 4
Introduction
1.2 SAFETY
MAINS VOLTAGE.
This equipment operates from an AC power source of between 90 and 265 volts. There are hazardous
voltages present internally. PLEASE OBSERVE CAUTION WITH THE COVER REMOVED.
SWITCHED MODE POWER SUPPLY HAZARD
Please note that the power supply units in this equipment is of the switched mode variety and have lethal
voltages present internally. The switched mode supplies are universal input fully approved type. They are
non serviceable modules and should be fully replaced should they fail.
FUSES
Only use fuses with the specified voltage and current ratings as stated on the back panel. Failure to do so
may increase the risk of equipment failure, shock and fire hazard.
R.F.
The N type R.F. power output socket contains R.F. voltages which may burn or present a shock. Please
make sure that the equipment is connected to an adequately rated load or antenna system while in opera-
tion.
TOXIC HAZARD
This equipment includes R.F. components that may contain Beryllium oxide which is a highly toxic sub-
stance that could be hazardous to health if inhaled or ingested. Care should be taken when replacing or
discarding such devices. Seek expert advice from the manufacturer should you physically damage a device
that contains Berillyium Oxide.
The main R.F. output power transistor contains Beryllium oxide.
OTHER SAFETY CONSIDERATIONS
Do not operate this equipment in the presence of flammable gases, fumes or liquids
Do not expose this equipment to rain or water.

TX25/50 FM Transmitter technical manual page 5
Introduction
1.3 FRONT AND REAR PANELS
FUSE
1234567 8 9 11 13
1210
TX25/50 FM TRANSMITTER
1. Left audio input 2. Left Input gain 3. Right input gain 4. Right audio input 5. MPX output 6. MPX level control 7. MPX Input 8. Control / Logic 9. R.F. output 10 LCD display 11. Power socket 12. Up / Down frequency buttons 13. Chassis ground post.
Control / logic D-type pin out Pin 1 PLL failure alarm (O/C) Pin 2 Reserved Pin 3 Reserved Pin 4 R.F. failure alarm (O/C) Pin 5 R.F. failure alarm (TTL) Pin 6 Mod failure alarm (TTL) Pin 7 PLL failure alarm (TTL) Pin 8 R.F. Mute (Connect to GND for mute) Pin 9 Mod failure alarm (O/C) Pin 10 RS232 TXD Pin 11 RS232 RXD Pin 12 Reserved Pin 13 Reserved Pin 14 +18 VDC 200mA Pin 15 GND
XLR Audio input connectors Pin 1 Ground Pin 2 Hot Pin 3 Cold
3
21
15 14 13 12 11 10 9
8 7 6 5 4 3 2 1
Front panel: R.F. MONITOR: -50dBC ( Not suitable for harmonic measurements ) MOD. MONITOR: ( Buffered multiplex, Nominally 3 V peak to peak for 75 KHz )

TX25/50 FM Transmitter technical manual page 6
Introduction
1.4 CONTROL AND MONITOR LCD
The front panel LCD graphics display has seven screens (shown below). These allow monitoring of the transmit-
ter’s R.F., audio and other parameters and the adjustment (if internally allowed) of the transmitter’s power and fre-
quency. You can move through the screens by pressing the NEXT button, which will display them in the following
order.
Main parameter screen.
This shows together the three most important transmitter
parameters. Frequency, R.F. output power and the peak
deviation.
Frequency display and control
This screen will display the frequency and PLL locked condi-
tion. The up and down buttons will allow 100 KHz frequency
steps from 87.5 to 108Mhz if the internal switches are set to
4440. If the frequency is set internally with the rotary switch-
es then the up / down buttons will give a ‘not allowed’ mes-
sage
R.F. power
The forward and reverse R.F. powers are displayed. The
up/down buttons will allow power control if internally allowed.
The maximum output power is governed by the maximum
power set adjustment (see R.F. pwr control section). If the
frequency is set internally with the rotary switches then the
up / down buttons will give a ‘not allowed’ message
Peak deviation
This display indicates the peak and average deviation. Peak
deviation is shown both numerically and as a moving single
pixel wide bar. Average deviation is shown with the solid
black bar. Over-deviation will display an exclamation ( ! )
Gain reduction
This display indicates the amount of gain reduction of the
internal audio limiter. The range is 0 to 24 decibels of gain
reduction.
Power supply
Power amplifier voltage is shown together with the transmit-
ters secondary supply that feeds the exciter section. The
power amplifier voltage will vary depending on set output
power and the presence of any fault conditions which also
cut the voltage back and with it the R.F. output.
P.A. temperature
This display indicates the temperature of the heatsink that
the R.F. power transistor is bolted to. The normal operating
temperature range is 40-60 degrees at full R.F. power out-
put.

TX25/50 FM Transmitter technical manual page 7
Installation and setup
2.1 FREQUENCY SETUP
The Frequency can be set on the transmitter in one of two ways:
1. From internal direct reading decimal switches on the main board
2. From the front panel LCD display and front panel buttons.
Many radio regulatory bodies stipulate that the transmitters parameters including the frequency must not be easily
changed from the front panel. To meet this requirement you will need to set the frequency internally with the dial
switches.
The switches have a silkscreen diagram next to them on the board (see diagram below) clearly indicating what
each switch represents.
The top dial switch represents the value selected x 10 Mhz with the exception of ‘0’ which represents 10 so when
selected would equal 100 Mhz.
The second dial switch represents the value selected x 1 Mhz.
The third dial switch represent the value selected x .1 Mhz (100 KHz)
The bottom switch represents the value selected x .0125 Mhz (12.5 KHz)
For example:
FREQ SWITCHES (MHZ)
X10 X1 X.1 X.0125
87.90 ‘8’ ‘7’ ‘9’ ‘0’
98.75 ‘9’ ‘8’ ‘7’ ‘4’
100.00 ‘0’ ‘0’ ‘0’ ‘0’
104.225 ‘0’ ‘4’ ‘2’ ‘2’
108.00 ‘0’ ‘8’ ‘0’ ‘0’
As you can see, the switches directly read the frequency with the exception of
frequencies above 100 Mhz, where the top switch being set at ‘0’ represents
‘10’. The X0.125 ‘offset’ switch is only used when you want to provide a shift to
the carrier of between 12.5 KHz and 112.5 KHz. Note that setting the switch
on 8 or 9 will have the same effect as setting the previous switch (100 KHz) 1
position higher, as 8 represents 100 KHz on the 12.5 KHz switch. 8 x 0.125MHz = 0.1MHz = 100KHz
The LCD display on the front panel will display the frequency that you have set on the internal switches. If you try
to adjust the frequency with the front panel up / down buttons you will get a ‘ NOT ALLOWED ‘ message appear-
ing on the LCD display. This protects against unauthorized front panel frequency changes when the frequency
has been set internally with the dial switches.
The TX will load the switch values at power up. You will need to remove the mains power to the transmitter
and then reapply it if you want to change the frequency by using the direct reading switches
LCD front panel frequency selection.
If you want to control the frequency from the front panel LCD control
system you will need to set the internal switches to 4440. The trans-
mitter will pass frequency control to the LCD control system and the
frequency can be moved up and down by pressing the NEXT button
until the frequency menu is displayed. The other two buttons control
the UP and DOWN frequency selection. PLL lock status is also dis-
played on this screen.
The LCD readout will only display frequencies in 100Khz steps. Any frequency offsets derived from the
internal 12.5KHz offset switch will not show on the LCD. Consult a frequency counter if using offsets.
Note that some pcb’s have “set to 4444 for
front panel LCD control”. This is an error that
will cause a +50KHz offset to the frequency
set on the LCD screen. Please set to 4440
unless you specifically want the offset.
Frequency selection switches on main board
Fine frequency control. Do not adjust unless you
know what you are doing. Consult advanced setup
section of manual for more information.

TX25/50 FM Transmitter technical manual page 8
Installation and setup
2.2 R.F. POWER SETUP
The R.F. power output from the transmitter can be controlled by an analogue potentiometer (POT) or from the
front panel LCD screen or a combination of both.
ANALOGUE POWER CONTROL
If the frequency is set internally with the dial switches you will not be able to adjust the power from the LCD
screen. This is to comply with regulatory body’s that stipulate that the transmitter is not to have it’s parameters
adjustable from the front panel. In this case you must use the maximum power set control to set the transmitters
power. This control will give the full power range adjustment.
If the transmitter has been internally set to 4440 with the dial switches then you can also control the power from
the LCD screen’s R.F. power menu’s up and down buttons. A “not allowed” message will be displayed to the user
if the dial switches are not set to 4440
RS232 power control will over-ride the power control restrictions caused by having the frequency set
internally (not set to 4440).
DIGITAL POWER CONTROL
When the power is to be controlled from the front panel the max power set POT takes on a new role of setting the
maximum power of the transmitter. If you want the LCD screen to have full power range control of the transmitter
you will need to ensure that the max power set control is at maximum power. Otherwise your control range may
be limited. This feature enables you to limit the transmitters maximum power to a fixed level but to still allow the
LCD screen to provide adjustment of the R.F. power down from that maximum power set point. This can be desir-
able in transmitter hire situations where you wish to govern the maximum
output to a fixed level but to allow the customer (hirer of the transmitter) to
run the power of the transmitter at a lower level if they so decide.
The maximum power set is positioned to the lower left of the LCD screen on
some models, other models may not have the hole in the front panel and you
will need to remove the lid of the transmitter to access the adjustment which will be in the same position but on
the other side of the PCB. You will need a small ‘tweaker style’ flathead screwdriver to adjust the pot. This control
is quite delicate so try to not be too heavy handed in it’s adjustment.
Please note that the VSWR and temperature protection circuitry will turn back the R.F. power if a fault con-
dition exists. Make sure that you have a good VSWR (low reverse power reading) before setting the R.F.
power as the removal of a fault condition may cause the R.F. power to increase.
RF POWER MUTE (analogue)
There is a pin (8) on the back panel D-type that can be pulled low to mute the
transmitters RF power. The RS232 interface board also has a connection to mute
the RF this way. Consult the RS232 section of this manual for more information.
RF POWER MUTE (digital/RS232)
The transmitters RF power output can be muted via the RS232 control system.
Terminal software can mute/unmute the RF power with the ‘o’ and ‘f’ commands
respectively.
The windows application has a button that can toggle the RF output of the trans-
mitter.
please consult the RS232 section of this manual for more information on controlling the transmitter remotely.

TX25/50 FM Transmitter technical manual page 9
Installation and setup
2.3 ALARMS
The Transmitter has three alarms that can alert the broadcaster if one of the following fails:
R.F. POWER, PLL LOCK, MODULATION
The alarms when set are available on the back panel D-type. Each alarm has an Open collector and a TTL level
contact on the D-type. The alarm induced active open collectors can pull down any external signals and the TTL
outputs will provide a 5 Volt indication. The alarm is also visible if any RS232 monitoring is employed.
For the alarms to function correctly the transmitter must be left on the default menu screen. This is the screen that
displays frequency, R.F. power and peak deviation. To ensure that the alarm system functions correctly the trans-
mitter will return to the default menu screen if the LCD is left on another menu screen for more than 5 minutes.
R.F. POWER.
The R.F. power alarm will be set if the R.F. power falls below a threshold level during normal operation.
This threshold is set below the normal operating lowest wattage available from the transmitter. If you
require a different setting for the alarm, contact our tech dept. The alarm will only be set if the fault condi-
tion exists for sixty seconds or more. You will need to reset the transmitter to clear the alarm/s.( also see
RS232)
PLL LOCK.
The PLL lock alarm will be set if the transmitters falls out of frequency lock during normal operation. The
alarm will only be set if the fault condition exists for sixty seconds or more. You will need to reset the trans-
mitter to clear the alarm/s.( also see RS232)
MODULATION FAILURE.
The Modulation failure alarm will be set if during normal operation the peak deviation of the transmitter
drops and remains below 16 KHz. The 16 KHz alarm level allows the alarm to be set if the audio feed to
the transmitter fails even if the stereo pilot internal to the transmitter is still modulating the transmitter. The
alarm will only be set if the fault condition exists for sixty seconds or more. You will need to reset the trans-
mitter to clear the alarm/s.( also see RS232)
MORE INFO ON ALARMS
The three alarms are available on the back panel D-type connector. The pin-outs are shown on the rear
panel diagram. The three alarms are available as TTL level and as open collector outputs. The TTL level
outputs are active high in the event of an alarm. The open collector outputs are ON in the event of an
alarm and will pull down any external levels. The open collectors can sink 100mA MAX with an absolute
maximum switched voltage of 25 volts.
The D-type connector can also supply 18 volts at 200mA that can be used for pull-ups on the open collector
alarm outputs and for your own external switching circuitry. Broadcast warehouse can also supply custom
plug in PCB’s for the D-type that will allow N+1 control. Two transmitters can be installed in the same rack
and in the event of an alarm being set the external PCB will switch between the main and standby trans-
mitters and if needed switch a coaxial relay.
The RS232 interface provides the ability to reset the alarms. More info is found in the RS232 section of
manual.
Broadcast warehouse can also customise the alarm / fault software to meet the requirements of major
broadcasters and networks. More information on this and other custom features can be obtained from our
technical department.

TX25/50 FM Transmitter technical manual page 10
Installation and setup
2.4 RS232 CONTROL AND MONITORING
The TX range of transmitters can be monitored or controlled from a personal computer either locally or remotely.
The Transmitters can “chat” either by a windows application or via a standard serial terminal program. The win-
dows application is the more versatile option and is to be preferred but the ability to use a terminal program can
prove useful in the absence of the windows application or a computer that runs windows.
2.41 RS232 interface board
To connect your TX series transmitter to your serial cable you will need the optional BW TX series RS232 inter-
face board (shown). This board provides
the level conversion required for RS232.
The board also provides an interface to
the various control and alarm signals
present on the transmitters 15 way D-
type connector. For further details of the
alarms please see the back panel con-
nection page of this manual.
The Interface board will push into the
transmitters D-type connector and you
can then break out your other signals via
the push/snap terminals. a 9 way serial
lead from your computer can be plugged
into the expansion boards 9 way D-type
socket..
The above item is an optional extra and
is available from broadcast warehouse and it’s distributors
2.42 Windows application (TXCTRL.EXE)
The latest version of TXCTRL.EXE can be downloaded from...
http://www.broadcastwarehouse.com/downloads
Installation
The windows application is a single file executable that
can be simply run by clicking on it’s ICON. The pro-
gram doesn’t require a setup program and can simply
be copied to the desktop and run as neccessary.
Setup and connection.
Once opened the application will resemble the picture
to the right.
Connect a serial cable between the RS232 board that plugs into the i-o D-type on the rear of the transmitter and
one of your computers COM ports. If you are using a codec or other device then you may be able to connect that
device in line to act as part of the serial link.
The application can connect to either COM port 1 or 2 on the computer that is running the application. Select the
TRANSMITTER
O/C Mod fail
O/C PLL fail
O/C R.F. fail
TTL R.F. fail
TTL Mod fail
TTL PLL fail
R.F. MUTE (PULL LOW FOR MUTE)
GND
COMPUTER
TX SERIES RS232 INTERFACE BOARD
TXCTRL startup screen