DRM
MF 455kHz -> AF Converter
(455kHz
down converter)
revision 1.2
MF (455kHz) to AF
(audio frequency) Converter/Interface
to receive DRM singals your shortwave receiver, like the Yaesu
FRG-100!
Please take also look at our
Digital Analog Demodulation Project (DADP, VE7DXW)
Attention! The
modification will be done at your own risk!
About the MF-LF converter/mixer:
This is a very
sensitive homemade MF converter/interface allowing you to receive
the DRM radio (Digital Radio
Mondiale) with your general
coverage receiver and a soundcard. It can also be used for
software radio apllications, and other MF to LF experiments (not
just DRM, and surely not just for the Yaesu FRG-100)
I've tested this project on a allmode Yaesu FRG-100 receiver.
Within certain limits you can change the output bandwidth
frequency to suit your needs. The converter is very stable, low
noise, sensitive and low on power consumption.
The heart of the converter has been built around Philips SA602
(NE602 or NE612), a twice balanced mixer oscillator. This IC
finds his applications in layer capacity communication systems,
cellular radio applications, RF data left, VHF-transceivers,
broadband LAN's ed. IC in a ordinary 8-pin dual-in-line can be
bought implementation (DIP) or 8-pin SO (surface-mount miniature
package) implementation. Both implementation has a low cost.
SA/NE602 a very low usage of only 2,4mA has! The total usage of
the converter amounts to only 15mA. Therefore also uncomplicated
usable applications fed with battery if needed, but in this
converter's DRM application I use the voltage of the receiver
itself.
The SA602A is a
low-power VHF monolithic double-balanced mixer with input
amplifier, on-board oscillator, and voltage regulator. It is
intended for high performance, low power communication systems.
The guaranteed parameters of the SA602A make this device
particularly well suited for cellular radio applications. The
mixer is a “Gilbert cell” multiplier configuration
which typically provides 18dB of gain at 45MHz. The oscillator
will operate to 200MHz. It can be configured as a crystal
oscillator, a tuned tank oscillator, or a buffer
for an external LO. For higher frequencies the LO input may be
externally driven. The noise figure at 45MHz is typically less
than 5dB. The gain, intercept performance, low-power and noise
characteristics make the SA602A a superior choice for
high-performance battery operated equipment. It is available in
an 8-lead dual in-line plastic package and an 8-lead SO
(surface-mount miniature package).
Revision 1.1(June
09)
I have added a low noise transistor (Q1) to amplify the output to
a more convenient level, as I noticed that the audio level was
just below the ideal level on one PC, whilest on my laptop the
level was enough. Remember to set the ideal audio volume level if
needed from within your OS.
R4 (already existing in rev.v1.0) and C13 gives some additional
filtering of the LF signal.
Revision 1.2(Nov
09)
I have noticed that by adding C17 hence limiting the highest
frequency responce and amplifying the lower 5...20kC gave
additional improvement.
P (trim pot) of 2k5 to allow exact LF output level setting for
your soundcard input
Voltage for Q1 now also 6 volt (tapped from IC2)
455KHz converter technical specifications
SCHEMATIC
PARTS
IC1 = NE602/SA602 or NE612/SA612
(all pin compatible)
IC2 = 78L06
Q1 = BC109,BC107
C1, C4 = 2.2uF/25v
C2, C3 = 100nF
C5 = 470pF
C6 = 100nF(polyester)
C7 = 68nF (polyester)
C8 = 100nF
C9 = 1nF
C10 = 820pF
C11= 100pF trimmer
C12 = 220pF
C13 = 1n5 (poly) v1.1
C14 = 220nF (polyester)
C15 = 2n2 (mylar,poly)
C16 = 220nF (poly) v1.1
C17 = 220pF v1.2
Cf = 465B (ZTB465Khz) ceramic filter resonator
R1*= 10k (not specified in the schematic, see text)
R2 = 1k8
R3 = 10k
R4 = 1k
R5 = 100k (v1.1)
R6 = 2k2 (v1.1)
R7 = 82 (v1.1) change
to lower value (or 0 Ohm) when not enough amplification for your
sound card input
P* = 2k5 (v1.2)
Ceramic resonator:
Cf is a simple 465 khz ceramic filter (3 pin or 2 pin
version can be used). These can sometimes be found in a AM/FM
transistor radio, old wireless telephones etc.
Ideal would be a quartz version as this offers best stability and
accurate resonating frequency of the mixer.
What's DRM
The Digital Radio Mondiale (DRM) purpose is to develop a
non-proprietary technical standard for the replacement of
analogue AM (Amplitude Modulation) radio with digital radio, also
called DRM.
As a replacement for AM the existing channel spacing, medium and
long wave 9 kHz and 10 kHz for short wave, is maintained. On
medium wave a DRM radio broadcast can provide close to FM audio
quality - most people will relate to the poor audio quality of AM
music. With DRM the audio quality is primarily determined by the
broadcast mode and spectrum occupancy (i.e. radio bandwidth of
the DRM signal).
It also the displays the name of the radio station, program text,
and automatic tuning to alternative frequencies will make DRM
receivers easier to operate. DRM can also transmit multimedia
html pages and data.
If you listen to a DRM signal on an ordinary short-wave AM radio
then all you will hear is noise. There is no discernible
modulation pattern when listening to DRM using a AM demodulator.
The (DRM) converter
explained using a Yaesu FRG-100
There are examples enough around
which use another filter by replacing the original LF-H2S with a
12kHz or 15kHz wide filter. This allowed the user to use DRM
reception by selecting the AM-narrow mode. The MF output is there
tapped from the (hot) connection of VR1002 as seen from the front
panel to the IF input of the converter(mixer).
In this modification I use the unused CW-filter connections hence
avoiding to remove the top board and soldering/replacing the
stock AMN filter. However, both methodes work.
Note: In this example DRM-mode is selected by selecting CW/N mode
on your FRG-100.
Calibrating
The converter is best calibrated
to fit 12 kHz wide LF output. C11 and C12 primary determines the
offset of the base resonating frequency of the 465kHz filter.
With a frequency counter you can check the resonating frequency
which should be around 467kHz. The converter/mixer outputs
467-455=12kHz wide AF output to be fed to your PC's soundcard
input.
Set C11 to get as close as possible to 467kHz. It is possible
that C12 need to be changed to if the desired frequency isn't
reached.
I have found that it isn't too critical, although calibrating
gives the best result. However, it should work as is (set C11 to
half way).
Set R3 to the best signal/noise ratio, hence also setting the
maximum output of the converter.
Note:
You can add a trim pot of +/- 2k5 at the output of Q1 after C16
to set the ideal output for your soundcard input. If want a
higher output level then simply bridge R7 or experiment with R7.
Power source voltage
The converter Vcc voltage can be
tapped from just about anywhere in the FRG-100. You can use the
12 volt input, or tap from the 9volts running allover the board.
Tap often used is R1074 (closest to the front to the UB
connection of the mixer board) where you find +9volt.
Any voltage from 8 to 18 volts can be fed as the converter uses a
78L06.
Using the CW/N optional filter connections
red wire is the +9v tapped from R1074,
47k resistor and ceramic filter is connected to the CW/N filter
connector to get MF
It is perfectly possible to use the CW/N filter connections of
the FRG-100 to tap the MF 455kHz...465Khz to feed it to our
converter/mixer.
Use a 455kHz filter of 12...50kHz (often found in those old FM
transistor radios etc.). This is soldered between pin 1 (top one)
of CW/N filter connector P1002 and pin 4 of P1001 (bottom pin). A
47k resistor from P1002 pin 1 is fed to the input of the
converter.
If you can not find such a ceramic filter (doubt it) you can
replace it by a few caps (this is not a drop-in
replacement, but workable enough to use for DRM with good signals
till better is found).
Note: DRM-mode is selected by selecting CW/N mode.
I soldered several of the converter
grounds to the VFO chassis (approx. middle of the picture)
You can see the yellow/greenish 455kHz 20kc ceramic filter
(between the converter and the FM-unit)
On the right side you can see my homemade FM-module based upon
the Yaesu schematic found in the manual.
Output/tuning/setting
The output of the
converter is fed to your soundcard using a female connector (on
the backside of the receiver). I drilled a hole at the back of
the FRG-100 to mount a 3.5mm female connector.
Use shielded wire to connect the converter to the connector.
R3 sets the maximum level of the MF signal supplied, hence
adjusting R3 can improve the signal-to-noise ratio depending on
the input sensitivity of your soundcard and/or do to the MF
voltage input. Set R3 to 80% to start with. Adjust the adjustment
on the mixer board for a DRM-signal of approximately 50mV RMS.
This is how a typical DRM signal looks like
- Connect the
decoder software to the 12 kHz IF output of the converter.
- Set the input volume of your PC properly.
- Set your FRG-100 to CW/N mode.
- Tune to a good DRM signal (3995,5955,6095,13810Khz...).
...Note: I have found that by tuning +/- 3Kc
of the DRM signal, the quality improves. Experiment!
- Once you here the software decoding the DRM-signal you can
further tweak the settings as explained above. And, the software
itself has several settings that can improve the
reception/decoding capabilities.
Some examples of decoded DRM signals using this converter/mixer and a Yaesu FRG100
Example 1 of a decoded DRM signal - medium ideal reception conditions!
Example 2 of a decoded DRM signal - medium ideal reception conditions!
Example 3 of a decoded DRM signal - bad reception conditions!
Software
- Googling around
will surely give you alot of software for DRM reception. I would
like to recommend DREAM.
Note on DREAM
DREAM is a software implementation of a Digital Radio Mondiale
(DRM) receiver.
All what is needed to receive DRM transmissions is a PC with a
sound card and
a modified analog short-wave (MW, LW) receiver.
http://drm.sourceforge.net
The necessary Qt runtime library "qt-mt230nc.dll" can
be downloaded at:
http://prdownloads.sourceforge.net/netclipboard/qt-mt230nc.dll?download
Optional download: AMSchedule.ini
Get the current shortwave broadcasting schedule for AM stations
from:
http://drm.sourceforge.net/download/AMSchedule.zip
Tip
* This converter can also be
used to feed a LF-amplifier (listen to signals unfiltered)
* Works with some software defined radio (SDR) programs, like
SDRadio from I2PHD!
* Use it to analyse wide band spectrum
* Modify the converter to allow even wider bandwidth by changing
the resonating ceramic filter
More about the SA602 (NE602,SA612,NE612) in this project
The SA602A is a Gilbert cell, an
oscillator/buffer, and a temperature compensated bias network as
shown in the equivalent circuit. The Gilbert cell is a
differential amplifier (Pins 1 and 2) which drives a balanced
switching cell. The differential input stage provides gain and
determines the noise figure and signal handling performance of
the system.
The SA602A is designed for optimum low power performance. When
used with the SA604 as a 45MHz cellular radio second IF and
demodulator, the SA602A is capable of receiving -119dBm signals
with a 12dB S/N ratio. Third-order intercept is typically -13dBm
(that is approximately +5dBm output intercept because of the RF
gain).
Besides excellent low power performance well into VHF, the SA602A
is designed to be flexible. The input, RF mixer output and
oscillator ports can support a variety of configurations provided
the designer understands certain constraints, which are explained
here.
50Mc converter de ON6MU
SDRadio
FRG-100 audio improvement
Dream v1.16 compiled version
Example of a decoded DRM signal
Technical graphs:
Please also look at our Digital Analog Demodulation Project (DADP, VE7DXW) that explains in high detail how to use it for the Yaesu FT-817 and simular transceivers
More about these mods:
50Mc converter de ON6MU
SDRadio
FRG-100 audio improvement
Dream v1.16 compiled version
Example of a decoded DRM signal
Ham mods modifications
Please take a look at my 50MHz converter which is ALSO based on the SA/NE 602 mixer!
50 MHz converter, 6 meter, 6-meter, 50Mc, antenna, radio amateur. Use a beam and receive distant VHF signals! using NE602 home made
Note: if you want to
commercialise, publish or distribute this project
then you need to ask permission to do so.
Attention! The modification will be done at your own risk!
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