My 5th receiver, a National RF-B60 bought in April 1988 in Japan, is a really good and sensitive receiver. It covers the Medium Wave (522 kHz - 1620 kHz) and has three overlapping Short Wave bands (1711 kHz - 29999 kHz) in 1 or 5 kHz steps. The selectivity is exellent and the reception on short wave is excellent. It also has the Japanese FM-Band (76-108 MHz) and the Air Band (108-137 MHz). There are 9 memory channels for every band (45 in all). The receiver shows good performance, the selectivity is good and the sensitivity is excellent, even if you use the Telescopic Antenna.

The internal LR6 batteries do not last extremely long, so it is advisable to use an external 6 V DC adapter. I am using a Friwo 230V / 3 VA adapter set to 6 Volt output..

There is a choice between a telescopic antenna or an external antenna which is connected via a 3.5 mm plug, there is a DX / LOCal switch, but you need to modify the radio to create a 450 kHz IF output which can be used for the a DRM IF converter.

Fig. 1

Break loose two IC socket pins from a 14-pin IC socket and use for the 450 kHz IF output. Solder these to the IF transformer on the RF-B60 printed circuit board. There is no need for retuning, and the IF output does not impair the reception or decrease its sensitivity in any way.

Fig. 2

Fig. 3

The 450 kHz to 10 kHz converter is the same as the previously described with two CB Quartz crystal oscillators and a simple FET Mixer. The circuit is very stable and works fine down to less than 8 Volts supply voltage. The 460 kHz output is generated from the heterodyne between two CB crystals. The output from the two oscillators are fed to the FET mixer, which has a 455 kHz IF Transformer in its drain.

The 450 kHz IF output from the receiver is fed through a filter which includes a 450 kHz Murata ceramic filter to decrease the DRM bandwidth. The IF signal is a little bit on the weak side, so I included an amplifier after the ceramic filter. The amplifier is provided with a gain control on the front panel. The amplitude of the 10 kHz IF output can also be adjusted with a potentiometer on the front panel of the converter.

Fig. 4