MFC: MF 455kHz -> AF Converter
revision 1.3

DRM converter interface 455khz
MF (455kHz) to AF (audio frequency) Converter/Interface
to receive DRM singals your shortwave receiver, or use with software to use it as SDR

Example here is applied in a Yaesu FRG-100!
Please take also look at our Digital Analog Demodulation Project (DADP, VE7DXW)
yaesu FRG-100
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, SA612), 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 13mA. 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)

Revision 1.3b(Nov, 21/26th 09)
C19& C18 added as it gave a noticable cleaner signal but lower LF output
R7 removed to compensate lower LF output
3b: added C18

455KHz converter technical specifications


homemade MF->AF converter


IC1 = NE602/SA602 or NE612/SA612 (all are 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)
C14 = 220nF (polyester)
C15 = 2n2 (mylar,poly)
C16 = 220nF (poly)
C17 = 120pF
C18 = 2n2
C19 = 22nF (poly)
Cf = 465B (ZTB465 kHz, or 470 kHz) ceramic filter
R1*= 10k (not specified in the schematic, see text)
R2 = 1k8
R3 = 10k
R4 = 1k
R5 = 100k (
R6 = 2k2
P* = 2k5 (

Ceramic resonator:
Cf is a simple 465 khz ceramic filter (3 pin or 2 pin version can be used). These can often 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.
There are many out there that are not exactly on frequency! When using it for DRM the mixing frequency is not critical, so you can use a 470 kHz type too.
If the bandpass is not 12 kHz and the frequency is too high you will need to adjust the mixing frequency Cf by using C11.
If the bandpass does not reach 12kHz because of the mixing frequency being too low you will need to add a capacitor in series with the ceramic resonator Cf, something between 100pF and 300pF. I would recommend starting with 150pF (or use a trimmer).

- ceramic filters can be order here (only EU)

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.

DRM Stations recent schedule list


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).
HOWEVER, 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.


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. Experiments with only 10...11kc bandwidth gave less satisfactory but still workable results.
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 sets the maximum output of the converter.
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.

If the bandpass is not 12 kHz and the frequency is too high you will need to adjust the mixing frequency Cf by using C11.
If the bandpass does not reach 12kHz because of the mixing frequency being too low you will need to add a capacitor in series with the ceramic resonator Cf, something between 100pF and 300pF. I would recommend starting with 150pF (or use a trimmer).

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

Yaesu modsred 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 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.


homemade DRM Converter mixer in Yaesu
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.


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 +/- 2Kc of the DRM signal, the quality improves. Possible reason could be the sound card timing accuracy, as on another PC the DRM frequency was exact. 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


- Googling around will surely give you alot of software for DRM reception. I would like to recommend DREAM.
downoad the compiled version
Here on our site you can find interesting software not only for DRM but other possibilities for the use of this converter!


DRM reception with the Yaesu FT-817

We use the optional CW or SSB Filter slot in the main unit. You must have this slot free (no optional filter) for using DRM on this radio.
The 455 KHz Signal for the DRM mixer can be easy taken from the first pin (from right) of J21 connector and connect the ground of cable to the second pin.
Now put a 455kc resonator between the first right pin of J20 and the first right pin of J21. Note: You can use simular like used in the FRG-100 please see fig2.
If you do not have a 455kc resonator then a capacitor of +/- 120 pf will be do, but you loose the agc advantages.

Switch on the rig and enter in the Menu System (press and hold the [F] key for on second) and choose Menu Item 38 [OP FILTER] setting mode CW.

You can activate now the DRM reception using the function NAR of the operation menu and setting CW MODE.

DRM reception with the Yaesu FT-897

Look for the slots for optional CW or SSB filter (backside, left) It’s labelled: J24 and J23.
Bridge the left two pins of J24 – so the software will use this slot as if the SSB filter is installed.
Put a 455kc resonator between the right pin of J24 and the right pin of J23. The third pin of J23 is connected to ground.
If you do not have a 455kc resonator then a capacitor of +/- 120 pf will be do, but you loose the agc advantages

Connect the DRM converter to the two right pins of J23 (ground and 455 kHz IF in).
I tapped 13 volts from the 8 volt voltage regulator (see on photo lower right corner). This connection is in consistency with the power on/off state of the rig.
For using the converter you have to enable the 2.3 kHz optional Filter setting in Menu (that’s the reason for the J24 jumper)

drm using a FT-897


* 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, weather satellite decoding etc.
* Modify the converter to allow even wider bandwidth by changing the resonating ceramic filter
* Can of course be used by any receiver that has a 455kHz MF you can tap.


More about the SA602 (NE602) in this project

The SA602A/SA612AN 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.

Dream v1.16 compiled version
Example of a decoded DRM signal

This is how Tonino IZ6QTX made it and how he is using it:
Thank you Tonino!

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
Dream v1.16 compiled version
Example of a decoded DRM signal

SA602/NE602 based converter for 6-meterband to 10-meterband
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