picture from: https://swling.com/
the National Radio Company HRO-500 was a completely solid state communications receiver with a frequency range greater than that of any other produced unit. All facilities were incorporated for AM, CW, and SSB reception between five kilohertz and 30 megahertz, with unusually accurate dial calibration, high frequency stability, and ease of operation. The HRO-500 was in use by every major government agency in the United States for HF/VLF point-to-point communications, monitoring, marine communications and for laboratory instrumentation applications, and rapidly became accepted as the finest and most versatile commercial receiver available for those use. Complete transistorization provided a very high MTBF, together with minimal heat generation and power requirements, the HRO-500 was remarkably compact in size and weight and may be either table or rack mounted. In addition, a fully portable version was available with self-contained power, loudspeaker, and waterproof carrying case.
FREQUENCY RANGE: 5 kHz to 30 MHz in sixty 500 kHz bands continuous coverage.
MODES: Selectable upper or lower sideband, MCW, FSK, AM, CW.
1. 117/234 V A.C 50-6O hertz;
2. 12.6 V.D.C
CALIBRATION ACCURACY: Within one kHz per 500 kHz band
SYNTHESIZER ACCURACY: Within 250 hertz over entire tuning range when zeroed at 10 MHz.
RESET ACCURACY (Including Visual Error): Within 250 hertz
TUNING DIAL BACKLASH: Less than 50 hertz.
TUNABILITY: Within 2 hertz
CALIBRATOR: 50 kHz crystal controlled.
R.F. INPUT IMPEDANCE: 50 ohm unbalanced (nominal); also separate high impedance unbalanced input for use with random antennas
SENSITIVITY (500 kHz-30 MHz):
A. AM (Nominal): Better than 2.0 uV for 10 db S/N
B. SSB/CW (Nominal): Better than 1.0 uV for 10 db S/N
A. 6 db bandwidths available; 500 hertz; 2.5 kHz, 5.0 kHz; 8.0 kHz.
B. Filter Design: six.pole LC type operating at 230 kHz; tunable through 6 kHz range in 500 hertz and 2.5 kHz bandwidth
C. Filter shape factor (Nominal): 2.5:l (6-60 db) in 2.5 kHz bandwidth.
D. Audio filtering provisions incorporated in LF-10 preselector.
IMAGE REJECTION (500 kHz-30 MHz.): Averages 80 db; minimum 50 db
SPURIOUS RESPONSES TO OFF-TUNE EXTERNAL SlGNALS: Minimum 50 db rejection.
AGC: Time constant; 60 millisecond attack, 3 sec delay AGC merit; average 5 db output change for input increase from la to 100,000 uV
AUDIO OUTPUT DISTORTION (Nomlnal): O.5 watts, 3.2%; 1.0 watts, 4.4%; 2.0 watts, less than 10%.
METERING: Front panel meter calibrated in db above 1.0 uV and from O to S-9 between no-signal and 4O db above 1.0 uv.
SIZE: 7 5/8″ H, 16 1/2″ W 12 3/4″ D
WEIGHT: 32 pounds
ALTERNATE CONFIGURATIONS: RMK 5 rack mounting kit for HRO 500 installation (per Mil Std. 189) in 8 3/4 H x 19″ W rack space; HRO 500P portable version with built in loudspeaker, self contained rechargeable battery power, and waterproof carrying case
ACCESSORIES: LF-10 (five kHz 500 kHz preselector); HRO 500 TS matching table speaker (7 3/8″ H x 5 29/22″ W x 12 3/4″ D); WPC 5 waterproof carrying case.
Radio Room M/V OPSANGER c/s JWRN