Daniels MT-3 Manuale utente
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Revision:
Revision Date:
Daniels Electronics Ltd.
Victoria, BC
PRINTED IN CANADA
MT-3 LOW CURRENT
FRONT END
INSTRUCTION MANUAL
132-174 MHZ 406-470 MHZ
Covers Models:
A11-FEF3/150
A11-RFAMP3/150
A13-FEF3/400
A13-RFAMP3/400
IM11-FE3
2-0-2
Aug 2005
MT-3 Low Current Front End Instruction Manual
IM11-FE3
ii
This document has been produced, verified and controlled in
accordance with Daniels Electronics’ Quality Management System
requirements.
Please report any errors or problems to Daniels Electronics’ Customer
Service Department.
The user’s authority to operate this equipment could be revoked through
any changes or modifications not expressly approved by Daniels
Electronics Ltd.
The design of this equipment is subject to change due to continuous
development. This equipment may incorporate minor changes in detail
from the information contained in this manual.
DOCUMENT CONTROL
NOTE
MT-3 Low Current Front End Instruction Manual
IM11-FE3
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Contents
General Information ...............................................................1
Introduction ................................................................................................1
Performance Specifications ....................................................................... 1
Theory of Operation ...............................................................3
General ......................................................................................................3
Power and Interconnection ........................................................................3
Five Pole Helical Filter ............................................................................... 3
RF Amp ......................................................................................................4
Image Rejection Filter ................................................................................4
Local Oscillator Input .................................................................................4
Double Balanced Mixer ..............................................................................4
Front End Alignment ..............................................................5
General ......................................................................................................5
Repair Note ................................................................................................5
Recommended Test Equipment .................................................................5
Check Points ..............................................................................................5
Tuning Procedure .......................................................................................6
MT-3 Front End Removal and Installation ..................................................6
Illustrations and Schematics ..................................................7
VHF Front End Component Layout ............................................................8
UHF Front End Component Layout ...........................................................9
VHF/UHF Front end Schematic diagram ................................................. 10
VHF/UHF front End Tuning Diagram ....................................................... 10
Parts List ...............................................................................11
Electrical Parts List .................................................................................. 11
Mechanical Parts List ............................................................................... 13
Revision History ................................................................... 15
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GENERAL
INFORMATION
INTRODUCTION
The MT-3 Front End is a highly integrated,
frequency selective, down converter used in
Daniels Electronics standard MT-3 FM receiver
product line. RF signals at the antenna input
are filtered by a 5 pole helical filter, amplified
through a low noise amplifier, filtered again
by a seven pole low pass or high pass filter,
and then mixed, with an externally supplied
local oscillator, to produce an IF frequency of
21.4 MHz. The Front End’s two main bands of
operation are 132 to 174 MHz and 406 to 470
MHz. Power for the Front End is supplied from
the receiver’s regulated +9.5 volts at a typical
current consumption of 8 mA. All Front End ports
(antenna input, local oscillator input, and IF
output) are designed for 50 Ω terminations.
PERFORMANCE SPECIFICATIONS
Frequency Range: 132 MHz - 174 MHz (VHF)
406 MHz - 470 MHz (UHF)
Bandwidth (3 dB): greater than 5 MHz (VHF Preselector Filter)
greater than 7 MHz (UHF Preselector Filter)
Conversion Gain: typically 12 dB (VHF)
typically 6 dB (UHF)
IF Frequency: 21.4 MHz
Local Oscillator Injection: +7 dBm maximum, high or low side injection
depending on frequency band
Impedance: 50 Ω at all ports
Power Requirements: 8 mA at +9.5 Vdc
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THEORY OF
OPERATION
GENERAL
The MT-3 Front End consists of a five pole
helical resonator filter structure with a single
stage, low noise, bipolar amplifier followed by
an image rejection filter and a double balanced
mixer. The highly selective narrow bandwidth of
the helical filter provides high out-of-band signal
rejection, high receiver spurious response, and
high wide band intermodulation attenuation. The
low noise amplifier increases receiver sensitivity
while the image rejection filter increases the
receiver’s image frequency attenuation. After
filtering and amplification, the received signal
is down converted to 21.4 MHz by a double
balanced mixer. The MT-3 Front End is built in
a VHF (132 to 174 MHz) and two UHF (406 to
430 MHz and 450 to 470 MHz) versions. MT-3
Front End tuning over the respective frequency
ranges is done through helical filter adjustment
and image rejection filter selection.
POWER AND
INTERCONNECTION
The MT-3 Front End operates from +9.5 Vdc
applied via a short red wire connected to supply
point J6-2 on the receiver main IF/audio board.
Ground return is supplied via direct mounting
to the receiver chassis and coaxial cable
interconnections. The MT-3 Front End draws
approximately 8 mA from the IF/audio board’s
+9.5 Vdc supply.
The RF input signal connected to the receiver
front panel type N connector is fed to the front
end SMB input connector (J1) by a short coaxial
cable. The MT-3 Front End’s local oscillator
input and IF output are respectively routed by
coaxial cable from the local oscillator module
and to SMB connector J7 on the main IF/audio
board.
FIVE POLE HELICAL FILTER
The received RF signal is filtered by a five pole
helical resonator band pass filter. This filter
provides front end selectivity and attenuates any
potential internally generated spurious signals.
Typically, the filter has an insertion loss of 3 dB
and a 3 dB bandwidth of 5.0 MHz in the VHF
range and an insertion loss of 4.5 dB and a 3 dB
bandwidth of 7.0 MHz in the UHF range. The
filter is tunable from 132 to 174 MHz for VHF
applications and 406 to 430 MHz or 450 to 470
MHz for UHF applications through adjustment of
the helical filter’s five trimmer capacitors.
MT-3 Low Current Front End Instruction Manual
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Theory of Operation
4
RF AMP
The output from the five pole helical filter is
coupled through impedance matching network
L4 and C9 to the base of RF amplifier Q2. The
RF amplifier stage is supplied by the regulated
+9.5 Vdc line and typically draws 8 mA of
collector current. Transistor Q2 provides high
gain, typically 20 dB in the VHF band and 16 dB
in the UHF band, and low noise figure typically
2.5 dB in the both bands, for increased receiver
sensitivity. Transistor Q1 actively regulates
the bias to RF transistor Q2. The output signal
is coupled to an image rejection filter via
impedance matching network C11 and L2 (VHF)
or L3 (UHF).
IMAGE REJECTION FILTER
The amplified RF signal is followed by a 7 pole
Chebyshev lowpass or highpass image rejection
filter which further rejects the image frequency.
The image filter topology (either lowpass or
highpass) depends on if the Front End is using
lowside or highside local oscillator injection. The
lowpass image filter consists of capacitors C16
to C19 and inductors L8 to L10. The highpass
image filter consists of capacitors C12 to C15
and inductors L5 to L7. Jumpers JU1 and JU2
are used to select the appropriate filter for the
desired receive frequency band. The table below
summarizes the receive frequency, whether
lowside or highside injection is used, and which
filter is installed.
MT-3 Front End Image Filter Selection
Frequency Band Local Oscillator Injection Image Filter
132 to 150 MHz Highside: RF + 21.4 MHz Lowpass: JU1 and JU2 - B side installed
150 to 174 MHz Lowside: RF - 21.4 MHz Highpass: JU1 and JU2 - A side installed
406 to 430 MHz Highside: RF + 21.4 MHz Lowpass: JU1 and JU2 - B side installed
450 to 470 MHz Lowside: RF - 21.4 MHz Highpass: JU1 and JU2 - A side installed
470 to 490 MHz Lowside: RF - 21.4 MHz contact factory
490 to 512 MHz Lowside: RF - 21.4 MHz contact factory
Note: There is an error in the silkscreen on PCB v1.0. JU1 A & B designations are reversed.
LOCAL OSCILLATOR INPUT
The MT-3 Front End local oscillator input port
(50 Ω) connects directly to a double balanced
mixer (M1). Any one of Daniels Electronics MT-3
Synthesizer modules or MT-3 Crystal Controlled
modules provide a suitable RF local oscillator
source. The local oscillator input level should
never exceed +7 dBm (5 mW into 50 Ω)
DOUBLE BALANCED MIXER
Double Balanced Mixer, M1, down converts
the received signal to 21.4 MHz. The mixer has
a maximum conversion loss of 7.5 dB and its
maximum local oscillator drive level is +7 dBm.
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GENERAL
Alignment for the MT-3 Front End consists of
tuning the five section preselector filter only.
No tuning is required for frequency changes
within the 3 dB bandwidth of its originally tuned
frequency (5 MHz for VHF and 7 MHz for UHF);
although, without tuning at the 3 dB band edges,
the receivers sensitivity will be degraded. For
frequency changes outside of the Front End’s 3
dB bandwidth, use the tuning procedure outlined
below.
REPAIR NOTE
The MT-3 Front End employs a high percentage
of surface mount components which should
not be removed or replaced using an ordinary
soldering iron. Removal and replacement of
surface mount components should be performed
only with specifically designed surface mount
rework and repair stations complete with Electro
Static Dissipative (ESD) protection.
When removing Surface Mount Solder Jumpers,
it is recommended to use solder wick braid in
place of vacuum type desoldering tools. This will
help prevent damage to the circuit boards.
RECOMMENDED TEST
EQUIPMENT
Alignment of the MT-3 Front End requires the
following test equipment or its equivalent:
Power supply - Regulated +9.5 Vdc
Spectrum Analyzer with Tracking Generator
Alignment Tool - Johanson 8764
CHECK POINTS
Vsupply: +9.5 Vdc @ 8 mA
Preselector Filter Insertion typically VHF: 3 dB;
Loss: UHF: 4.5 dB
RF Amplifier Gain: typically VHF: 20 dB;
UHF: 16 dB
Image Rejection Filter Loss: 1.5 dB maximum
Mixer Conversion Loss: 7.5 dB maximum
Test Point #1 (TP1): +7.4 Vdc
Test Point #2 (TP2): +8.0 Vdc
Local Oscillator Frequency: RF Frequency ± 21.4
MHz
FRONT END
ALIGNMENT
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Front End Alignment
6
TUNING PROCEDURE
The best way to tune the MT-3 Front End is to use a Spectrum Analyzer with a tracking generator.
The frequency response of the Preselector Filter can be seen at the IF output. Use the following
procedure for swept frequency tuning:
1) Check to see if the correct image rejection filter is selected for the frequency
of interest. This operation requires removing the Front End’s shield lid and changing
the solder jumpers if required.
2) Supply +9.5 Vdc to the MT-3 Front End (red wire).
3) Connect the Tracking Generator output with the Front End’s RF input. The tracking
generator should have an output level of -20 dBm and a frequency span of at least 10 MHz.
If the preselector filter is grossly misaligned, a larger frequency span may be required.
4) Adjust the helical filter trimmer capacitors for a flat response centered at the desired
RF frequency. The measured input level should be approximately -25 dBm and the
3 dB bandwidth should be 5 MHz and 7 MHz in the VHF and UHF range respectively.
MT-3 FRONT END REMOVAL AND INSTALLATION
The MT-3 Front End is fastened to the main board (MT-3 Receiver IF/Audio Board) with a single
Phillips screw to the Type F connector and to the front panel with two countersunk Phillips screws.
Remove these screws and disconnect the IF, LO, and power cables to remove the VHF / UHF Front
End. Installation of the MT-3 Front End is performed in a fashion reverse to the above procedure.
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