Marine Receiver – National HRO 500

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Dear Sparks,

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
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




Marine Receiver – Volna K

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Dear Sparks,

today we look over the old iron curtain to discover one of the receivers used on soviet cargo ships.

The Volna-K is a Russian Navy HF receiver. It was intended as a maritime receiver for the Navy and for commercial shipping.  It is a superheterodyne double conversion HF receiver, using 17 miniature valves, and 2 semi-conductor diodes. The valves have Russian numbers, but are equivalent to common American types. It can run off 110 or 220 volts AC, or 28 volts DC. It is intended to receive AM and CW signals down to  0.5 uV levels. The word “volna” translates to “wave”. The frequency coverage is 12 kHz to 23 mHz in 9 bands, with gaps around the IF frequencies. There are 3 versions of the Volna-K, each with a slightly different frequency coverage. There is also Volna-P which is the version for submarines.

                   VOLNA-K               VOLNA-K1               VOLNA-K3
Band 1       12  –   60 KHz        12   –     60  KHz       12   –    60 KHz
Band 2     100  – 180 KHz      100   –   180  KHz       60   –  100 KHz
Band 3     180  – 330 KHz      180   –   330  KHz     100   –  180 KHz
Band 4     300  – 600 KHz      300   –   600  KHz     180   –  330 KHz
Band 5      1.5  –  2.8 MHz      600   – 1100  KHz     330   –  600 KHz
Band 6      2.8  –  5.0 MHz       1.1   –    1.6  MHz    600   – 1100 KHz
Band 7      5.0  –  9.0 MHz       5.0   –    9.0  MHz     1.1   –   1.6  MHz
Band 8      9.0  – 15.0 MHz       9.0  –  15.0  MHz     1.6   –    2.8 MHz
Band 9    15.0  – 23.0 MHz     15.0 –   23.0  MHz     2.8   –    5.0 MHz

It was made in the Petropavlovsky Radio Factory,  in Kirov, USSR. About 70,000 were made from 1959 to 1985.

In the centre of the front panel, is the large semicircular dial (used for coarse frequency setting), and an optical frequency readout above it (for fine frequency setting). The maritime distress frequencies are marked, 500 khz and 2182 khz. It takes 40 turns of the heavy flywheel knob to go from band end to end, which is about 9 feet of tuning scale on the ground glass screen.

The Volna-K is a double conversion superheterodyne LF and HF receiver. It is single conversion on bands below 600 kHz. The first IF is 915 kHz and the second IF is 85 kHz, and there are gaps in the frequency coverage to allow for this, 60-100 khz and  600-1500 khz.

It has a conventional power transformer and double diode rectifier (5U4). The primary can be set for 110, 127, and 220 volts AC. There is a voltage regulator valve for the oscillator HT voltage and a barreter for current regulation of the oscillator heater. The mains power supply unit could be replaced by an optional 24 VDC supply.

It is a beautiful receiver, very easy to use, and very sensitive. There is so much gain, that when receiving SSB or CW signals




Marine Receiver – JRC NRD-1EL

Dear Sparks,

today it is the time of one old but good receiver made by JRC the model NRD 1EL built for merchant marine communications and largely used on ships of all flags. NRD-1EL has been a joint venture between JRC and Collins, the VFO was a PTO concieved for 1 MHz excursion.

Year: 1965

Bands: 30 bands in 1 MHz each

Frequecy coverage: from 90 kHz up to 30 MHz

Priciple: supereterodybe triple conversion

Filters: Xtal filters 6/3/1 kHz

Tubes: 20 tubes + transistors

Charateristics: 19 inches for rack mountage

The Japan Radio Company is one of the old radio factory founded in 1915. For long time it has been the largest wireless factory of the world in the fields of marine, aero, land mobile and satellite communications.




Marine Receiver – Marconi Nebula

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Dear Sparks,

the receiver considered in this review is the Marconi Marine model NEBULA largely employed on merchant ships also as emergency receiver, at first the receiver was made by the Eddystone Company and known as model EC 958/5 than branded “Nebula” under the MIMCO (Marconi International Marine Company) and labeled also HAGENUK EE 430.

NEBULA Receiver

Type: General purpose, superheterodyne receiver which uses single, double or triple conversion depending upon the frequency which is being received.

Frequency Range: 10 kHz to 30 MHz in ten overlapping ranges.

IF frequencies: 1st IF 1335 kHz; 2nd IF 250 KHz; 3rd IF 100 KHz

Modes: CW, MCW, AM (DSB) and SSB in A3A. A3H and A3J modes (upper or lower sideband) with selectable sideband switching. FSK (Fl) facilities can also be used by fitting an optional module within the receiver proper. Keying speeds up to 200 baud with shifts of 85 to 850Hz can be accommodated.

Semiconductor Complement: The entire circuit including the optional FSK module makes use of 41 transistors, 54 diodes and 12 integrated circuits.

Selectivity: Five degrees of selectivity are provided ranging from 400 Hz for narrow-band CW to 8 kHz for AM.

Power Mains:  Single-phase AC mains 100/125 and 200/250V (40 to 60Hz), or low-voltage DC using external DC/ AC converter. Consumption is in the order 35 watts AC or . 45 watts DC.

Vintage: Manual is dated 1971

Weight: 41.75 lbs

Dimensions: 16.75″W x 18″D x 5.75″H

Comments: Can easily be converted to a rack mount unit.




Marine Receiver – Redifon R 408

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Dear Sparks,

this time we remember the well know receiver REDIFON R 408 one of the first receiver properly realized with both SSB mode (USB and LSB), the receiver, fully transistorized (except the oscillator for 500 kHz with one tube), employed the Loop of Wadley and it was very stable indeed, with this receiver frequency drift was over.


Country                    Great Britain U.K.

Year                          1968

Producer                  Redifon Ltd.; London

Category                   Professional receiver

Principle: Supereterodyne double / triple conversion; ZF/IF 80 kHz
Gamme d’onda Medium Wave (MW), Long Wave (LW) and Short Wave (HF)
Power supply 100-125 Volts; 200-250 / 24 Volt (battery)
Audio power out 1.4 W (excellent quality)
Material Metal cabinet
Dimension(LxHxD) 420 x 220 x 500 mm / 16.5 x 8.7 x 19.7 inch
Notes Communications receiver for maritime use, coverage 13 – 28000 kHz, AM, USB/LSB, CW;
Single conversion below 650 kHz, depending on frequency, first IF is 470 kHz, 1.5 Mhz or 4.5 Mhz, second IF 80 kHz. Internal crystal calibrator, analog film tuning scale.
This receiver was also used in in ship wireless stations equipped by German maritime telecommunications company Hagenuk as Receiver Hagenuk E 408R.
Weight 25.5 kg / 56 lb 2.7 oz (56.167 lb)



siemens e311

Marine Receiver – Siemens E311

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Dear Sparks,

a great receiver produced by Siemens largely employed on merchant ships but concieved for many other brands of radiocommunications.

Shortwave Communications Receiver
Triple Conversion Superheterodyne
17 Tubes + Semiconductors
Made in West Germany 1960 – 70’s


Coverage: 1.5 – 3.5 / 3.4 – 7.6 / 7.5 – 15. 1 / 15.0 – 22.6 / 22.5 – 30.1 MHz
Antenna Input: SO-239 60 Ohm unbalanced
Sensitivity: CW (0.3 kHz filter): 0.16 µV 6 dB S/N,
AM (6 kHz filter): 1.5 µV 10 dB S/N,
SSB (3.5 kHz filter): 0.7 µV 10dB S/N
Setting & Read out: 100 Hz
Stability: +/-20 Hz over 24 hours (after warm up of ovens)
Selectivity: 6/3/1/0.3 kHz -6 dB, formfactor 6/60 dB 1:2.2 for AM and 1:1.3 for SSB
IF: 1st IF: 1300-1400 kHz, 2nd IF: 370 kHz, 3rd IF: 30 kHz
IF Rejection: >80 dB
Image Rejection: >80 dB
Audio Output: 1 W/5 Ohm, 600 Ohms line
Voltages: 110/125/220/235 V AC +/-10% 40-60 Hz, average 70 W
Physical: Cabinet Version: 471x291x391 mm, 25kg
Shock Mounting Frame: 498x328x420 mm
Accessories: E 350 long wave adapter 10-1500 kHz, FSE 30 or TG 440 (Teletron)
for FSK, H 305 for space diversity, Hellfax BS 110 or 114 for fax,
NZ 3101 (Rohde&Schwarz) for ISB reception


– 1/4” Head Jack (2) – Speaker – Speaker Switch – Line Out 600 Ohm
– BFO 1000 Hz – ANL – S/AF Meter – AGC/MGC
– AGC 0.2/2 sec. – Squelch – IF Output Jack – Ref. Osc. Oven
– Spectr. Osc. Oven – RF Gain – Calibrator 100 kHz – Dial Lamps
– Dial Adjust – Dial Lock – Fine Tuning – Spinner Knobs
– Preselector – Semi-Modular – Rack Handles


Circuit Complement
Tubes + Semiconductors: 3x EF 93 (=6 BA 6), 5x ECH 81 (=6 AJ 8), 8x E 88 CC (=6922), 1x 85 A 2, germanium, selenium and silicon rectifiers, zener diodes for voltage regulation, 4x germanium transistors in power supply and 11x in 1 kHz spectrum oscillator, ovens for VFO and 100 kHz spectrum unit.
Tuning: Four ganged capacitively tuned preselector circuits. Coarse tuning via 1st oscillator  continuously or in steps of 100 kHz (phase locked to a spectrum oscillator in an oven). RF conversion to 1st IF (1300 to 1400 kHz), fine tuning between lock-in steps via 2nd oscillator (930 to 1030 kHz, in an oven) for further conversion to 2nd IF (370 kHz). The 2nd oscillator can be locked to an optional 1 kHz spectrum unit. 4 circuits for RF, 7 for 1st IF, 8 for 2nd IF and 8 for 3rd IF (SSB).
Crystals: 1x 100 kHz for calibration and spectrum unit, 1x 340 kHz + 1x 400 kHz in 3rd oscillator (USB/LSB) for 3rd conversion to 3rd IF (30 kHz), 1x 30 kHz + 31 kHz in BFO (SSB/CW) for 4th conversion (product detector) to AF.
Dials: Dial for coarse setting in 100 kHz steps. Fine tuning dial (between 0 and 100 kHz) of odometer type with 100 Hz readout . Both dials are driven by spinner knobs and gears.


This receiver was designed in 1959 for AM, CW, FSK and SSB reception. It was widely used by different government authorities and in military applications. It could be found on board of most German ships in the Sixties and Seventies. As a tube receiver the E 311 has an incredible setting accuracy of 100 Hz and an impressive stability of 20 Hz over 24 hours. The tuning scale has an effective length of 285 m (935 feet). Excellent for AM reception in an ECSS mode as well. The E 311 is probably one of the best tube receivers for FSK and SSB ever built.


Versions E 311a to E 311e are very similar. Only small changes mostly in power supply, audio stages and 100 kHz spectrum unit were made. The E 311e1 and E 311e2 are the cabinet versions; the E 311e3 and E 311e4 have a shock mounting frame. E 311e2 and E 311e4 include the optional 1 kHz spectrum unit.






Marine Receiver – Allocchio Bacchini AC20

Dear Sparks,

in Italy there have been some industries produced marine radio gears during the “Radio Golden Age”, one of them was a big factory located in North Italy with name RADIALBA or well known as ALLOCCHIO BACCHINI very famous for the production of domestic radios and first TV sets. This time it is proposed the Marine Receiver model AC 20, these radios have been used on board for more than 20 years from their date of built, very nice audio quality also if the receiver suffered of a certain drift never solved definetively because of its own project: Rotating Drum with tuned tanks, anyway the AC 20 has been very popular among Italian Radio Officers. Unfortunately on the web there are not videos about this receiver. Below the characteristics:

AC20 – Allocchio Bacchini

Paese: Italia

Producer:   Allocchio Bacchini (Radialba); Milano

Anno:  1956

Categoria: Professional receiver

Valvole: 13: 6CB6 6CB6 6BE6 6C4 6BE6 6BA6 6BA6 6BA6 6AL5 6BA6 12AU7 6AQ5 0A2

Principle:  supereterodyne double / triple conversion; ZF/IF 950/62 kHz; 2 Stage AF

Tuned tanks:  9 Circuits

Power supply:  AC voltage 110 or 220 Volts

Speaker: output for external speakers or headphones

Audio power:  2 W (excellent quality)

Model: AC20 – Allocchio Bacchini Radialba

Materials: metal cabinet

Dimension (LxHxD):   490 x 300 x 405 mm / 19.3 x 11.8 x 15.9 inch

Frequency coverage:  75 kHz – 31 MHz

Weight:   25 kg / 55 lb 1.1 oz (55.066 lb)




Marine Receiver – MACKAY 3010 C

Dear Sparks,

to remember the MACKAY receiver model 3010 C installed on many anglosaxon ships..

Country: USA

Producer: Mackay Radio & Telegraph Company; New York

Alternative name: ITT Mackay Marine

Year: 1968

Category: Professional receiver

Tubes  17: 7788 6C4 6688 6BL8 6BE6 6BA6 6BA6 6AV6 12AT7 6BF5 6BL8 6U8 6EW6 6BA6 6BA6 6AU6 0B2

Principle: Supereterodyne double / triple conversion; ZF/IF 455 kHz

Bands: MF HF

Power supply:  AC / 115 Volt

Model: 3010-C – Mackay Radio & Telegraph

Materials: Metal cabinet

Dimension (LxHxD): 19 x 10.5 x 16 inch / 483 x 267 x 406 mm

Notes: Coverage (10 kHz)70 kHz to 30 MHz in 15 bands, works in AM, CW, MCW, SSB and FSK, S-meter, BFO, triple conversion ~38 MHz, 5,94 MHz and 455 kHz, 90 inch film scale, differences to the type B are just added capacitors to improve the frequency stability.




Marine Receiver – Siemens 745 E 310 or Debeg 566

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Dear Sparks,

waiting for MRD this time is proposed the good German receiver Siemens 745 E 310 or Debeg 566, the receiver was used also in other brands of radiocommunications but largely on merchant ships.

General Coverage Communications Receiver
Double Conversion Superheterodyne
17 Tubes + Semiconductors
Made in West Germany 1956 – 1971


Coverage: 14 – 21 / 85 – 175 / 170 – 350 / 340 – 730 / 720 – 1540 kHz
1.5 – 3.1 / 3.1 – 6.3 / 6.0 – 10.2 / 9.7 – 15.2 / 14.7 – 20.2 / 19.7 – 25.2 / 24.7 – 30.2 MHz
Modes: AM/CW/MCW
Antenna Input: SO-239 75 Ohms unbalanced
Sensitivity: CW: 0.3 µV 6 dB S/N, AM: 8 µV (LF-MF), 4 µV (HF) 10 dB S/N
Setting & Read out: 500 Hz
Selectivity: 6.2/2.4/1.8 kHz –6 dB. In the 14 – 21 kHz and 85 – 175 kHz ranges 0.8 kHz –6 dB.
Formfactor -6/-60 dB: 1:2.8 at 6.2 kHz bandwidth.
IF: 1st IF: 1080-1180 kHz, 2nd IF: 100 kHz
IF Rejection: 50-70 dB, typically 70 dB
Image Rejection: 40-80 dB
Audio Output: 1.6 W/5000Ohms, 600 Ohms line
Voltages: 110/125/220/250 V AC +/-10% 40-60 Hz, 100 W
Physical: Cabinet Version: 550x350x380 mm, 35kg
  Rack Version: 520x304x380mm
Accessories: FSE 2 or Teletron TG 440 for FSK, FSE 7 or Hellfax BS 110 for Fax


– Headphone Jack – Speaker – Speaker Switch – Line Out 600 Ohms
– BFO +/-3 kHz – ANL – AGC/MGC – AGC 0.1/1sec.
– RF Gain – Calibrator 100 kHz – Dial Lamp – Two Tuning Speeds
– Fine Tuning – Break In Relay – Semi Modular – Rack Handles


Circuit Complement
Tubes + Semiconductors: 4x EF 93 (=6 BA 6), 3x EK 90 (=6 BE 6), 4x ECC 82 (=12 AU 7), 2x EAA 91 (=6 AL 5), 1x EL 90 (=6 AQ 5), 1x EM 34 (=6 CD 7), 1x 108 C 1 (=0B 2), 1x 150 C 2 (=0A 2), selenium rectifiers in power supply.
Tuning: Three ganged capacitors in RF circuits, three ganged capacitors in 1st variable IF-circuits. Continuos tuning by a knob (transmission 10:1 pushed and 160:1 pulled) via 1st oscillator. Alternatively above 1.5 MHz exact setting of 1st oscillator in steps of 100 kHz with calibrator for RF conversion to variable 1st IF (1180 to 1080 kHz), fine tuning via 2nd oscillator (1280 to 1180 kHz) for further conversion to 2nd IF (100 kHz).
Crystal: 1x 100 kHz for calibration.
Dials: Very big colorful coarse dial, first segment is fine tuning dial 100 kHz.


This model was designed for the marine market replacing the E 61, E 66a (LF, HF, 1948), E 303, E 305 and E 306 (all HF, 1952-1954). The E 310 was licensed as a class one receiver by Deutsche Bundespost. A standard receiver like competitor Hagenuk UE 12 on German ships. The twelve bands are selected by push-buttons on the left. Called “parrot cage” by the operators, referring to its colorful dial. Quite suitable for SSB reception using the product detector at 1.8 kHz bandwidth in CW mode.


The E 310b has a C-type antenna jack instead of the SO-239 jack. The E 566 is a very similar model, first with a dark green cabinet and front panel, later often light gray.

Best regards,



Marine Receiver – Marconi ATALANTA

picture by LU5FBX

Dear Sparks,

waiting for the Maritime Radio Day we will propose a revival of marine receivers many of us used during the Radio Golden Age. The receiver proposed this time is the MARCONI ATALANTA largerly used on Merchant ships but it has been reported it was employed in the Navy to.

Country of production:  Gran Bretagna (Regno Unito)

Factory:  MIM, Marconi International Marine; Chelmsford Essex

Year: 1958

Tubes:  14

Type of receiver:  Supereterodyne  double / triple conversion

Power supply:  220/24 Volt (and battery)

Audio power:  1 W

Name of RX:  Model: Atalanta 2207C – MIM, Marconi International

Materials: Metal cabinet

Dimension (LxHxD):  495 x 319 x 503 mm / 19.5 x 12.6 x 19.8 inch

Description: Complete coverage is provided by the receiver over the frequency band 15 kc/s. to 28 Mc/s. in ten ranges, with band spread scales directly calibrated in frequency for the six H.F. marine bands. Additionally, electrical fine tuning of 3 kc/s. Provides signal tuning discrimination of great accuracy. The wide frequency range available and the complete coverage of the receiver makes it suitable for mobile, maritime or fixed stations having to receive signals from a wide range of transmitting sources.
The receiver, which is normalcy mounted in a bench-type cabinet may, to meet special requirements, be fitted on a standard 19-inch rack. The “Atalanta” operates directly from 110 or 220 volts D.C., or 115 or 230 volts A.C. in conjunction with the necessary power units.
The receiver covers the band 15 kc/s. to 20 Mc/s. in ten ranges as follows:
1. 15-25 kc/s. (20,000 – 12,000 m.)
2. 25 – 100 kc/s. (12,000 – 3,000 m.)
3. 100-200 kc/s. (3,000 – 1,500 m.)
4. 200 – 400 kc/s. (1,500 – 750 m.)
5. 400-800 kc/s. (750-375 m.)
6. 800 kc/s. – 1.4 kc/s. (375 – 176.4 m.)
7. 1.7- 3.6 Mc/s. (176.4 – 83 m.)
8. 3.6 -7.5 Mc/s. (83 – 40 m.)
9. 7.5 – 15 Mc/s. (40 – 20 m.)
10. 15 – 28.0 Mc/s. (20 -10.7 m.)
Intermediate Frequency: On ranges 1, 3, 4, and 5 I.F. of 85 kc/s
On range 2 and ranges 6 to 10 a I.F. of 700 kc/s and a 2nd I.F. of 85 kc/s.

Weight: 35.4 kg / 77 lb 15.6 oz (77.974 lb)

Best regards,