LPF-100 technical manual
Broadcast Devices, Inc.
LPF-100 Composite
Low Pass Filter
TECHNICAL REFERENCE MANUAL
Broadcast Devices, Inc.
2066 E. Main Street
Cortlandt Manor, NY 10567
Tel. (914) 737-5032
Fax. (914) 736-6916
REV: A 03/09
2
Table of Contents
The LPF-100 Low Pass Filter
I.
Introduction
A. Unpacking and Inspection
B. General Description
II. Specifications
III. Installation
A. Initial Configuration
B. Location and Hookup Considerations
C. Composite Connections and Adjustments
D. Composite Loop Out Connection
E. Stereo Generator Alignment
IV. Warranty
V. Schematic Diagrams
A. Overall Schematic
3
Introduction
A.
The LPF-100 Low Pass Filter is intended to be used in conjunction with suitable FM stereo
generators and/or composite STL for the purpose of reducing the amount of noise present
generated by aggressive audio processing, STL noise or unintended signals that can
sometimes be generated by stereo generators.
B. Unpacking and Inspection
Carefully unpack the unit after receipt and inspect for damage that may have occurred during
shipping. If damage is noted, contact the shipper immediately and file a damage claim. The
contents of the package have been insured to cover total replacement cost. Make certain that the
package contents are the same as noted on the packing slip. If not, contact Broadcast Devices,
Inc. Check to make sure all mechanical parts are secure. Units are delivered from the factory
configured for 120 volts A.C. 60 Hz. Operation. Check to make sure that the power source is
correct for proper operation. Units are field configurable for 240 Volt operation. See initial
configuration section of part III, installation section for different power configuration.
B. General Description
The LPF-100 accepts an FM stereo base band signal from a suitable stereo generator or
studio to transmitter link receiver. The signal is fed to a 10th order linear phase low pass filter
whereby signal information above 53 KHz is filtered. The unit features balanced or
unbalanced input and three outputs suitable for driving 50 ohm coaxial cable. There are two
outputs on the rear panel to be fed to the unbalanced or balanced input of an FM exciter and
one on the front panel for test purposes.
II. Specifications
Input Impedance:
Output Impedance:
Maximum Output level:
Gain:
Frequency Response:
Total Harmonic Distortion:
Inter - Modulation Distortion:
System Noise:
Input Connectors:
Output Connector:
Power Requirements:
Operating Temperature Range:
Physical Dimensions:
10K or 50 ohm balanced/unbalanced selectable
50 ohms unbalanced
3.5 Volts Peak to Peak into 50 ohms
6 dB variable
Better than +/- 0.1 dB from 10 Hz to 40 KHz
-1.6 dB at 50 KHz, -50 dB at 100 KHz
Better than 0.05% into 50 ohms
Better than 0.05% S.M.P.T.E. 4:1
Better than 80 dB below 3.5 Volts Peak to Peak
1 - Isolated B.N.C.
B.N.C. (2 rear, 1 front panel)
120/240 Volts A.C. 50 - 60 Hertz
0 - 60° Celsius non condensing atmosphere
1.75 H X 19 W X 10 D (inches)
III. Installation
A. Initial Configuration
Before installing the unit it is a good idea to decide whether or not the unit will operate balanced
or unbalanced and/or bridging or terminated at its input. Generally, to avoid ground loops
between equipment it is advisable to operate the unit in the balanced configuration. If for some
reason it is desired to operate the units unbalanced and/or to terminate the input to 50 ohms,
locate the rear panel four position DIP switch. Push the switch section marked terminate down. If
unbalanced inputs are desired, push the switch position marked unbalanced down. The other two
switch positions have no function on this unit. Refer to the stereo generator or STL
4
manufacturer’s technical information to determine whether or not this equipment is capable of
being terminated by 50 ohms. When termination is used a reduction of available signal will occur.
This is due to the load and source impedance being matched thus reducing the signal available
by half. The LPF-100 has enough gain to overcome this loss. As shipped from the factory the unit
is adjusted for unity gain. To increase the gain, simply adjust the front panel control of each
output for proper level feeding the exciter.
The unit as configured from the factory is set to accept 120 Volts A.C. 60 Hertz electrical power.
To change the power setting, first remove the power cord from the power entry connector. Slide
the plastic cover to the left and with a pair of long nosed pliers carefully remove the power select
p.c. board from the power entry module. Select the desired power configuration by placing the
power entry p.c. board back into the module so that the desired power setting can be read from
left to right.
B. Location and Hookup Considerations
Locate the LPF-100 in a 19-inch E.I.A. standard rack enclosure in close proximity to the
equipment that it is going to interface between. Allow sufficient airflow space between equipment
to allow for proper cooling. It is important that the cables being fed from composite sources such
as stereo generators and STL receivers be kept as short as is practical. The LPF-100 can drive
lines at least as long as 25 feet with no degradation of signals. It is advisable to keep all cable
lengths as short as possible to prevent stray R.F. pick up.
C. Composite Connections and Adjustments
Make all desired input and output connections to your external equipment. Make sure that the
LPF-100 is plugged in to a properly grounded A.C. receptacle. If possible, interrupt the audio
feeding the LPF-100 and measure the signal to noise ratio with a suitable voltmeter. If the noise
measurement obtained is acceptable you can proceed to the final adjustment of the unit. If the
noise is high there may be stray R.F. pick up or a ground loop. It is a good idea to listen to the
system with a suitable audio monitor to determine the source of the noise. Hum is a common
noise present. If hum is present, start by removing one cable at a time to determine the source of
the ground loop. If the hum disappears or changes level when a cable is disconnected, a loop
exists between the LPF-100 and the equipment at the other end of the cable removed. This will
generally not happen with an input unless the unit has been configured for unbalanced operation.
If this is the case, try the balanced input mode of operation. If a ground loop is present between
the LPF-100 and an exciter or STL, feed the LPF-100 to a balanced input. Most modern exciters
accommodate balanced cables.
Note: Do not feed SCA, RBDS signals through the LPF-100 as they will be attenuated. The LPF100 is intended only for stereo base band signals. You must plan the routing of SCA and/or
RBDS signals around the LPF-100 for proper injection level to the exciter.
D. Composite Loop Out Connection
The LPF-100 is equipped with a loop out connection. The signal present at this connection is
the signal fed to the input of the unit before filtering. This connection is provided if it is desired to
have an unfiltered signal source available. It is recommended that if this output is used that the
input termination switch be left up in the bridging position.
E. Stereo Generator Alignment
Once the connections have been completed to the unit it is recommended that the respective
manufacturers’ instructions for aligning the stereo generator be followed. Addition of the LPF-100
5
may have an impact on the L=-R gain and the 19 KHz stereo pilot phase. Most modern stereo
generators have a range of adjustment of the L=-R gain and 19 KHz pilot phase to compensate
for transmission path amplitude and phase distortions introduced. A general procedure is given
below but it is strongly suggested that you obtain a copy of the technical information for your
stereo generator to follow the proper procedure.
General Stereo Generator Alignment procedure:
This procedure should be followed with the LPF-100 installed just before the composite inputs of
the exciters that it will be feeding with all other equipment in the signal path as it will be used on
the air. Failure to do this will result in misalignment of the system which can result in poor stereo
separation and or impaired signal to noise ratio.
The following test equipment is required for the following procedure:
1. Audio Oscillator
2. Oscilloscope with a vertical amplifier response of at least 500 KHz.
Left = - Right Gain adjustment:
The best way to insure proper performance is to monitor the stereo base band signal from the
output of a modulation monitor or wide band output of a suitable FM demodulator. The
modulation monitor RF input should be connected to a suitable directional coupler in the
transmitter RF output line. Attach the oscilloscope to a base band output of a modulation monitor
and adjust the vertical input so that the entire signal can be displayed from top to bottom on the
scope screen.
Feed a 50 hertz left or right only signal to the input of the stereo generator and observe the
oscilloscope waveform. The waveform will resemble a sine wave with a filled in area under the
curve. Carefully observe the base line. It should be flat. If it is concave or convex shaped adjust
the L=-R gain control until the base line is flat. The base line may appear to be thick this is the 19
KHz pilot riding on the base line. Refer to the figure below for a properly adjusted base line.
A properly adjusted L=-R gain adjustment 50 Hertz Left Only - Pilot has been removed
Pilot Phase Adjustment
Feed a 50 Hertz audio signal to both left and right inputs of the stereo generator but out of phase.
Observe the oscilloscope and note that you should see a pattern that resembles a butterfly.
Adjust the sweep of the scope so that the intersection of the butterfly “wings” is observed in the
middle of the scope screen. Adjust the vertical amplifier so that it is easy to observe the center of
the butterfly. Observe the 19 KHz pilot phase by observing the two triangular tips that point to one
another. If the pilot is properly adjusted the tips will be on the same horizontal line in the center of
6
the scope screen. If they do not line up horizontally the pilot phase will need to be adjusted.
Adjust the pilot phase so that the two tips meet horizontally.
A properly adjusted pilot phase indication as observed on an oscilloscope.
Audio
Oscillator
Stereo
Generator
LPF-100
Exciter/Xmtr.
Modulation
Monitor
Oscilloscope
Suggested Equipment Setup for stereo generator alignment
7
IV. Warranty
Broadcast Devices, Inc. products are warranted against failure due to faulty materials or
workmanship for a period of one year from the date of shipment to the ultimate user. The
warranty covers repair or replacement of defective parts at the factory, provided the unit has
been returned prepaid by the user. All shipments to the factory shall have affixed to the outside of
the container an R. A. number obtained from the factory. The above warranty is void if the unit
has been modified by the user outside of any recommendations from the factory or if the unit has
been abused or operated outside of its electrical or environmental specifications. If customer
conducted field tests suggest that the unit may be faulty, whether or not the unit is in warranty, a
full report of the difficulty should be sent to Broadcast Devices, Inc. factory at Cortlandt Manor,
New York. The office may suggest further tests or authorize return for factory evaluation.
Units sent to the factory should be well packed and shipped to Broadcast Devices, Inc. 5
Crestview Avenue, Cortlandt Manor, NY 10567. Remember to affix the R.A. number to the
outside of the carton. Any packages received without such R.A. number will be refused. Note:
freight collect shipments will also be refused. When the unit has been received, inspected and
tested, the customer will receive a report of the findings along with a quotation for recommended
repairs, which are found falling outside of the standard warranty. Units returned for in-warranty
repairs which are found not to be defective will be subject to an evaluation and handling charge.
In-warranty units will be repaired at no charge and returned via prepaid freight.
Out-of-warranty units needing repair require a purchase order and will be invoiced for parts,
labor, and shipping charges.
When ordering replacement part, always specify A) Part number or Description, and Quantity;
B) Date of Purchase, Where Purchased; C) Any Special Shipping Instructions. Always specify a
street address, as shipping companies cannot deliver to a postal box.
Broadcast Devices, Inc. is not responsible for any other manufacturer’s warranty on original
equipment. Nor are we responsible for any failure, damage, or loss of property that may occur
due to the installation or operation of our equipment outside of recommended specifications.
8
V. Diagrams
5
4
3
2
1
CR1
CR2
-DC
3
2
2
1N4007
C7
C3
4700uF 50V
-15V
3
Vo
C4
.1 50V
R5
120 1/2W
CR3
C5
1N4007 .1 50V
1
1
1N4007
Vi
ADJ
P3
U1
LM337
HDR3
.1 50V
CR4
D
C6
3300uF 25V
C10
R7
4.7uF 50V
1.3K 1/2W
D
1N4007
C12
CR17
.1 50V
U13 1N4007
LM7905
3
-5V
VOUT
VIN
2
CR18
GND
C65
.1 50V
C67
3300uF 25V
C66
.1 50V
1
1N4007
+DC
CR5
U4
LM317
3
Vi
.1 50V
C15
4700uF 50V
C16
.1 50V
Vo
+15V
2
R11
120 1/2W
CR7
C17
1N4007 .1 50V
1
CR8
1N4007
ADJ
CR6
1N4007
C19
1N4007
C25
C34
-15V
2
3
7
VR1
10K
+
8
7
6
5
-
1
2
3
4
4
S2
4.7uF 50V
R44
C
CR15
U11
1N4007
LM7805
1 Vi
Vo 3
OUTPUT 1
49.9 1/4W
U8
BUF634
C57
.1 50V
C43
+5V
CR16
C58
1N4007 .1 50V
C59
3300uF 25V
2
R46
1K 1/4W
C38
+15V
C40
R49
46.4K 1/4W
U7
AMP02
VR2
10K
C47
.1 50V
-15V
4.7uF 50V
J4
BNC
C50
1
8
6
5
C49
INPUT
C48
-15V
4
-
4.7uF 50V
2
3
53 KHz Low
Pass Filter
7
2
.1 50V
.1 50V
R47 46.4K 1/4W
7
+
4
3
INP
R48
46.4K 1/4W
+15V
4.7uF 50V
J6
BNC
R50
5
6
8
1
+
INN
C45
.1 50V
4.7uF 50V
R45
49.9 1/4W
B
J5
BNC
5
6
8
1
1.3K 1/2W
.1 50V
4.7uF 50V
-
LOOP OUT
J3
BNC
.1 50V
GND
C36
C
C18
3300uF 25V
C20
R14
R51
1K 1/4W
R22
1.3K 1/4W
R57
C51
-15V
1.3K 1/4W
+5V
CM5693
470 1/4W
C52
+15V
+15V
49.9 1/4W
U9
BUF634
DS1
R21
OUTPUT 2
.1 50V
B
4.7uF 50V
C53
-15V
4
C54
3
+
7
2
-
VR3
10K
.1 50V
4.7uF 50V
J7
BNC
R55
5
6
8
1
U10
BUF634
R56
1K 1/4W
C56
49.9 1/4W
Front
Panel Test
C55
.1 50V
+15V
4.7uF 50V
A
A
NOTE: ALL RELAYS SHOWN IN "POWER OFF" STATE
{}
Title
Size
C
Date:
5
4
3
2
Broadcast Devices, Inc.
LPF-100
Document Number
Rev
B
Sunday, March 08, 2009
Sheet
1
1
of
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