Japan Radio Company introduced the NRD-505, the company's first HF communications receiver for the amateur/SWL market, in 1977. The receiver features a PLL-based, double superheterodyne receiving system with 70.4555 MHz and 455 kHz intermediate frequencies. The receiver's PLL system uses a reference oscillator consisting of a high-stability permeability-tuned oscillator (PTO) VFO - a la Collins - and a voltage controlled oscillator (VCO), both housed in a die-cast aluminum case.
There are 30 fixed ranges of 1 MHz each selectable with a large rotating switch. Once the MHz band is set the main tuning dial is used to tune within that band. A digital readout displays frequency to 100 Hz resolution. A switchable 'Delta-F' control on the front panel allows precise fine tuning, without changing the digital readout. The '505 was used in some commercial applications (often with its matching NSD-505 transmitter), but JRC clearly designed the receiver for non-professional end-users such as shortwave listeners and amateur radio operators.
The '505 was the first SWL receiver to feature programmable memory channels with an optional 4-channel memory board (CDD-48), a $125 option. Other available options included the NVA-505 Speaker, a 0.6 MHz Mechanical Filter (Narrow CW), the NFG-505 Preselector, and the CGA-26 VFO Converter Unit for transceive operation with an external transmitter.
The physical construction of the NRD-505 reflects the professional heritage of JRC. The receiver uses a modular plug-in design for the internal printed circuit boards. Four of these boards comprise the RF portion of the receiver, while four additional boards, plus the previously mentioned VFO assembly, make up the frequency synthesizer section. Other plug -in boards include the memory board (optional, as described above), and a VFO converter (another option to connect the NRD-505 with a variety of transmitters for transceive operation). Fastened to the receiver's aluminum chassis are the various parts which make up the front panel and display circuit; the motherboard which all the circuit boards plug into; and the power supply. All circuit boards are high quality glass-epoxy type. Isolation between the circuit boards is excellent due to the heavy aluminum shielding between each board.
The modular design approach makes for a clean interior without the typical spaghetti-like wiring harnesses found in other conventional designs. A major benefit of modular construction is the easy installation of optional equipment. Troubleshooting is far less painful, too, as most problems can be narrowed down to a single circuit board with very little effort.
One thought that naturally comes to mind when looking back nearly 20 years: "How did JRC expect the average SWL to justify spending over two grand for a receiver?" The Yaesu FRG-7 was one of the most popular general-purpose SWL machines available up to that time, and you could have bought six of them and still have had some change left! At the same time, the Drake R-7 was achieving legendary status among DXers and had many features conspicuously absent on the '505, passband shift and notch filter the most obvious. And the R-7 cost only $1,295. In the late 1970's, $2,275 was a lot of money!
Performance-wise, the '505 held its own ground with other receivers of its era, such as the Drake R-7 and the '505's successor, the NRD-515. But the quality of construction put the NRD-505 in a league of its own in 1977. As one reviewer, Rainer Lichte, put it: "The price itself is not questionable; workmanship, quality of construction and life expectancy justify this price." Indeed, few radios before or since offer the same solid feel and rugged construction of the NRD-505.
The '505 is very simple to operate: just set the desired band with the "MHz" knob, then dial up the kHz with the main VFO dial. The main tuning has a concentric ring for high speed band scanning and a center knob for precise tuning. Both operate quite smoothly with no backlash. The frequency is displayed by a six digit LED readout and also by a conventional analog scale with 1 kHz markings. RF and AF Gain controls are located to the left of the main tuning dial, while the fine tuning (Delta-F) and BFO controls are just to the right. The Delta-F is enabled by one of five flat lever switches; the other switches select internal or external VFO (for use with the matching transmitter), engage the noise blanker and RF attenuator, and control the main power.
An additional row of push buttons are provided for the optional CDD-48 four-channel memory unit. To select a memory channel, simply set the preset/manual switch to the "preset" position and press the desired channel button (CH1-CH4). To store a frequency into memory from the "manual" mode, simply select one of the four channels and press the memory button on the far right hand side. Only the frequency is memorized, since mode and AGC is set with separate analog switches. Primitive by today's standards, but remember that we're talking about 1977! The idea of pressing a button or two and jumping between your four favorite stations was bordering on science fiction at that time.
When compared to later models, the '505 does surprisingly well for shortwave broadcast listening. The audio quality is quite good and AF output is more than enough to fill the room. Selectivity is not quite in the same league as the NRD-525 and NRD-535; these newer models both feature electronically tuned front end filters as opposed to the fixed-width bandpass filters used by the NRD-505 (and NRD-515). For this reason the NRD-505 is prone to front-end overload at lower frequencies. An optional outboard preselector, model NFG-505, was later offered to improve front-end performance. Even without a preselector, simply switching on the 20 dB attenuator clears up all but the most severe interference from nearby and out-of-band signals.
Like all PTO-based tuning systems, the '505 can not easily tune from the high end of one 1 MHz band to the low end of another. Comparing the signal quality of the BBC on 5.975 MHz vs. 6.175 MHz, for example, takes quite a bit of dial twisting; in addition to switching the "MHz" knob one position, the operator also must tune down from 975 kHz to 175 kHz. Continuous tuning was still a few years away.