Modification of Sony ICF-SW77
for DRM Software receiver
Date: 19-11-02
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1 Introduction
1.1 Purpose of this document
This document describes how to modify a Sony ICF-SW77 short wave receiver to be able to
receive a DRM signal. Therefore the DRM – Miniature Mixer Unit from Sat-Service
Schneider is used, to mix down the 455 kHz IF of the receiver to a 12 kHz IF. This 12 kHz IF
is feed to a PC sound card.
Please note that the manufacturer's warranty will be discarded if you do this modification.
1.2 Organization of this document
Chapter 1 provides an introduction to the document.
Chapter 2 provides an overview of the system.
Chapter 3 describes how the IF filter of the ICF-SW77 has to be changed.
Chapter 4 describes how the DRM Miniature Mixer Unit has to be connected to the receiver.
2 System overview
The 2. IF (455 kHz) of the ICF-SW77 receiver is feed to the miniature mixer unit and down
converted to a 12 kHz IF. This IF signal is then connected to the input of a PC sound card.
This PC decodes the DRM signal with a decoder software.
mixer
unit
455 kHz
12 kHz
ICF-SW77
PC
3 Change of 455 kHz IF filter
The bandwidth of the ICF-SW77 receiver is too small to receive a DRM signal. Therefore the
IF filter has to be changed.
3.1 Schematic
The following diagram shows the schematic of the SW 77 IF section.
Date: 19-11-02
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wide band filter
ZF in
GND
narrow band filter
The IF section has two IF filters, a narrow band filter and a wide band filter. One of these
filters has to be replaced by a wider filter with appr. 10 kHz bandwidth. The filter ‘W’ is
active if the receiver is in ‘wide’ mode, the filter ‘N’ is active if the receiver is in ‘narrow’
mode.
Date: 19-11-02
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3.2 Filter bandwidth
The with the receiver supplied wide band IF filter has a bandwidth ob appr. +/- 3 kHz. The
bandwidth is shown in following diagram:
The recommended replacement filter is a Murata CFWM455GY, which has the same
footprint as the original filter, but a bandwidth of appr. +/- 4,5 kHz. The bandwidth is shown
in following diagram:
Date: 19-11-02
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3.3 IF Filter types
The following Murata filter types are fitting into the IF filter footprint in the SW77 receiver:
Part Number
CFWM455G
CFWM455F
CFWM455E
6 dB bandwidth
+/- 4.5 kHz
+/- 6.0 kHz
+/- 7.5 kHz
4 Connection of DRM Miniature Mixer Unit
The IF frequency is 455 kHz in the SW77 receiver. Therefore the mixer unit with a 467,0 kHz
oscillator is needed. It is recommended to use the mixer unit with the crystal oscillator.
Date: 19-11-02
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4.1 Power supply
The mixer unit needs a power supply with 7-20 V DC. Unfortunately the receiver supplies a
maximum voltage of 6 V. Test showed that it is possible to use the 6V instead of the 7-20 V
to run the mixer unit. An other possibility is to remove the voltage regulator on the mixer unit
and replace it with a diode (e.g. 1N4007).
The 6V power lines of the mixer unit can be connected to the connector at the right side of the
PCB (back view). The +6V line is the most top solder point. The ground can be connected to
the last solder point of the connector.
It is recommended to use the external power supply and not the batteries when the receiver is
used as a DRM front end.
4.2 IF connection
The ‘hot’ line of the IF input should be connected to pin 14 of IC301. The ground connection
of the IF input should be connected to pin 12 of IC301.
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