For most of the 1990’s, the Japan Radio NRD-535D table top receiver was the best of the best, and the envy of every SWL around the world.
I acquired mine used in 1996. It was a joy to use, and I still have it. Even today, you will find the NRD-535D as a collector’s item. Leading edge features included exalted carrier single sideband (ECSS) reception for AM signals, variable bandwidth and passband reception, and what had to be the world’s smoothest tuning knob.
Founded in 1915, Japan Radio Co. Ltd. (Nippon Radio Telegraph and Telephony before 1942) focused mainly on maritime communications and navigation for many years. I discovered that JRC started making up-conversion synthesized communications gear in the 1970’s. My NRD-535D ran from 1991-1998.
Year after year, this radio got top marks in reviews. Owning one meant you had “made it” into the elite of short wave listening. Although mine is now thirty years old, the specs are pretty close to more modern gear, including SDR. About the only thing it lacks is DSP noise reduction. And, aesthetically, it’s beautiful.
The front end of the NRD535D featured microprocessor controlled filtering which reduced intermodulation. Analog notch was good for 40 dB and the noise blanker even worked on the dreaded “woodpecker” radar interference from Russia.
You had two downsides, though. Quite often AGC overshoot would cause popping, fixed by reducing RF gain. And the wonderful variable bandwidth resulted in weaker filter skirts, making the feature less useful in crowded bands.
NRD-535D Table Top Architecture
Up conversion became state of the art during the 1990s. You will find this became possible with the advent of cheap DDS frequency syntheses and monolithic VHF filters. My triple conversion NRD-535D table top has IF at 70 MHz, 455 and 98 kHz. Microprocessor control shifts the DDS up and down to create variable bandwidth and passband tuning against the filter slopes in the various IF chains.
I discovered that PC control of the NRD-535D was really simple, using plain text (ASCII) commands at 4800 baud over the serial port. If you are interested, here is a detailed review of this radio. Finally, you might enjoy this video demonstration of the NRD-535D table top in action.